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+</style><link href="http://www.w3.org/StyleSheets/TR/w3c-unofficial" rel="stylesheet" type="text/css" charset="utf-8" /></head>
+
+<body style="display: inherit; "><div class="head"><p></p><h1 class="title" id="title">RDF Graph Normalization</h1><h2 id="subtitle">A Standard RDF Graph Normalization Algorithm</h2><h2 id="unofficial-draft-16-october-2011">Unofficial Draft 16 October 2011</h2><dl><dt>Editors:</dt><dd><a href="http://manu.sporny.org/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
+<dd><a href="http://digitalbazaar.com/">Dave Longley</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
+<dt>Authors:</dt><dd><a href="http://digitalbazaar.com/">Dave Longley</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
+<dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
+</dl><p class="copyright">This document is licensed under a <a class="subfoot" href="http://creativecommons.org/licenses/by/3.0/" rel="license">Creative Commons Attribution 3.0 License</a>.</p><hr /></div>
+<div id="abstract" class="introductory section"><h2>Abstract</h2>
+<p>
+RDF [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SYNTAX">RDF-SYNTAX</a></cite>] describes a graph-based data model for making claims about
+the world and provides the foundation for reasoning upon that graph of
+information. At times, it becomes necessary to compare the differences between
+graphs, digitally sign graphs, or generate short identifiers for graphs via
+hashing algorithms. This document outlines an algorithm for normalizing RDF
+graphs such that these operations can be performed on the normalized graphs.
+</p>
+</div><div id="sotd" class="introductory section"><h2>Status of This Document</h2><p>This document is merely a public working draft of a potential specification. It has no official standing of any kind and does not represent the support or consensus of any standards organisation.</p>
+<p>This document is an experimental work in progress.</p>
+
+<!-- <p>
+This document has been reviewed by W3C Members, by software
+developers, and by other W3C groups and interested parties, and is
+endorsed by the Director as a W3C Recommendation. It is a stable
+document and may be used as reference material or cited from another
+document. W3C's role in making the Recommendation is to draw attention
+to the specification and to promote its widespread deployment. This
+enhances the functionality and interoperability of the Web.
+</p> -->
+
+</div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#how-to-read-this-document" class="tocxref"><span class="secno">1.1 </span>How to Read this Document</a></li><li class="tocline"><a href="#contributing" class="tocxref"><span class="secno">1.2 </span>Contributing</a></li></ul></li><li class="tocline"><a href="#normalization" class="tocxref"><span class="secno">2. </span>Normalization</a><ul class="toc"><li class="tocline"><a href="#normalization-algorithm-terms" class="tocxref"><span class="secno">2.1 </span>Normalization Algorithm Terms</a></li><li class="tocline"><a href="#normalization-state" class="tocxref"><span class="secno">2.2 </span>Normalization State</a></li><li class="tocline"><a href="#normalization-algorithm" class="tocxref"><span class="secno">2.3 </span>Normalization Algorithm</a></li><li class="tocline"><a href="#node-relabeling-algorithm" class="tocxref"><span class="secno">2.4 </span>Node Relabeling Algorithm</a></li><li class="tocline"><a href="#deterministic-labeling-algorithm" class="tocxref"><span class="secno">2.5 </span>Deterministic Labeling Algorithm</a></li><li class="tocline"><a href="#shallow-comparison-algorithm" class="tocxref"><span class="secno">2.6 </span>Shallow Comparison Algorithm</a></li><li class="tocline"><a href="#object-comparison-algorithm" class="tocxref"><span class="secno">2.7 </span>Object Comparison Algorithm</a></li><li class="tocline"><a href="#deep-comparison-algorithm" class="tocxref"><span class="secno">2.8 </span>Deep Comparison Algorithm</a></li><li class="tocline"><a href="#node-serialization-algorithm" class="tocxref"><span class="secno">2.9 </span>Node Serialization Algorithm</a></li><li class="tocline"><a href="#serialization-label-generation-algorithm" class="tocxref"><span class="secno">2.10 </span>Serialization Label Generation Algorithm</a></li><li class="tocline"><a href="#combinatorial-serialization-algorithm" class="tocxref"><span class="secno">2.11 </span>Combinatorial Serialization Algorithm</a></li><li class="tocline"><a href="#serialization-comparison-algorithm" class="tocxref"><span class="secno">2.12 </span>Serialization Comparison Algorithm</a></li><li class="tocline"><a href="#mapping-serialization-algorithm" class="tocxref"><span class="secno">2.13 </span>Mapping Serialization Algorithm</a></li><li class="tocline"><a href="#label-serialization-algorithm" class="tocxref"><span class="secno">2.14 </span>Label Serialization Algorithm</a></li></ul></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">A. </span>Acknowledgements</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">B. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">B.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">B.2 </span>Informative references</a></li></ul></li></ul></div>
+
+
+
+<div id="introduction" class="section">
+
+<!-- OddPage -->
+<h2><span class="secno">1. </span>Introduction</h2>
+
+<p>When data scientists discuss graph normalization, they
+do so in the context of achieving a particular set of goals. Since a directed
+graph can express the same information in a variety of different ways, it
+becomes necessary to be able to transform a graph of information into a
+standard form for the purposes of calculating differences between two graphs,
+generating a cryptographically-strong hash identifier for a graph, or digitally
+signing a graph.</p>
+
+<p>Many RDF graphs, containing nodes with unique identifiers, can be normalized
+quite easily. However, when a node does not have a unique identifier,
+graph normalization becomes exponentially more difficult. This problem is
+called the <dfn title="graph_isomorphism" id="dfn-graph_isomorphism">graph isomorphism</dfn> problem, and it is believed to be a
+NP-hard problem in the worst cases. This means that the problem is very
+difficult to solve in a reasonable timeframe for certain inputs. Luckily, these
+types of inputs are extremely rare in the real world. Graph isomorphisms are
+most commonly used as a denial of service attack and thus any software system
+attempting to solve the graph normalization problem should be able to detect
+graph isomorphisms correctly.</p>
+
+<p>This document outlines an algorithm for generating a normalized RDF
+graph given an input RDF graph. The algorithm is called the
+<strong>Universal RDF Graph Normalization Algorithm 2011</strong> or
+<strong>URGNA2011</strong>.</p>
+
+<div id="how-to-read-this-document" class="section">
+<h3><span class="secno">1.1 </span>How to Read this Document</h3>
+
+<p>
+This document is a detailed specification for an RDF graph normalization
+algorithm. The document is primarily intended for the following audiences:
+</p>
+
+<ul>
+ <li>Software developers that want to implement an RDF graph normalization
+algorithm.</li>
+ <li>Masochists.</li>
+</ul>
+
+<p>
+To understand the basics in this specification you must be familiar with basic
+RDF concepts [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-CONCEPTS">RDF-CONCEPTS</a></cite>]. A working knowledge of
+<a href="http://en.wikipedia.org/wiki/Graph_theory">graph theory</a> and
+<a href="http://en.wikipedia.org/wiki/Graph_isomorphism">graph isomorphisms</a>
+is also recommended.</p>
+</div>
+
+<div id="contributing" class="section">
+<h3><span class="secno">1.2 </span>Contributing</h3>
+
+<p>There are a number of ways that one may participate in the development of
+this specification:</p>
+
+<ul>
+<li>Technical discussion typically occurs on the public mailing list:
+<a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
+</li>
+
+<li><a href="http://json-ld.org/minutes/">Public teleconferences</a> are held
+on Tuesdays at 1500UTC on the second and fourth week of each month.
+</li>
+
+<li>Specification bugs and issues should be reported in the
+<a href="https://github.com/json-ld/json-ld.org/issues">issue tracker</a>.</li>
+
+<li><a href="https://github.com/json-ld/json-ld.org/tree/master/spec">Source code</a> for the
+specification can be found on Github.</li>
+
+<li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a>
+IRC channel is available for real-time discussion on irc.freenode.net.</li>
+</ul>
+
+</div>
+
+</div>
+
+<div id="normalization" class="section">
+
+<!-- OddPage -->
+<h2><span class="secno">2. </span>Normalization</h2>
+
+<p class="issue">This algorithm is a work in progress, do not implement it.</p>
+
+<p>Normalization is the process of taking <a class="tref internalDFN" title="input_graph" href="#dfn-input_graph">input graph</a> and
+performing a transformation on that input that results in all
+aspects of the graph being arranged in a deterministic way in the
+<a class="tref internalDFN" title="output_graph" href="#dfn-output_graph">output graph</a>. That is, for two <a class="tref internalDFN" title="input_graph" href="#dfn-input_graph">input graph</a>s
+containing the same
+information, regardless of their arrangement, the <a class="tref internalDFN" title="output_graph" href="#dfn-output_graph">output graph</a>s
+will be identical. The problem is a fairly difficult technical
+problem to solve because it requires a directed graph to be ordered into a
+set of nodes and edges in a deterministic way. This is easy to do when all of
+the nodes have unique names, but very difficult to do when some of the nodes
+are not labeled and thus names must be generated for those nodes in a
+deterministic fashion.
+</p>
+
+<p>In time, there may be more than one normalization algorithm that will need
+to be identified. For identification purposes, this algorithm is named the
+"Universal RDF Graph Normalization Algorithm 2011"
+(<abbr title="Universal RDF Graph Normalization Algorithm 2011">URGNA2011</abbr>).
+</p>
+
+<div id="normalization-algorithm-terms" class="section">
+<h3><span class="secno">2.1 </span>Normalization Algorithm Terms</h3>
+ <dl>
+ <dt><dfn title="input_graph" id="dfn-input_graph">input graph</dfn></dt>
+ <dd>
+ The data structure that is provided as input to the algorithm.
+ </dd>
+ <dt><dfn title="output_graph" id="dfn-output_graph">output graph</dfn></dt>
+ <dd>
+ The data structure that is produced as output by the algorithm.
+ </dd>
+ <dt><dfn title="label" id="dfn-label">label</dfn></dt>
+ <dd>
+ The subject IRI associated with a graph node.
+ </dd>
+ <dt><dfn title="list_of_expanded_nodes" id="dfn-list_of_expanded_nodes">list of expanded nodes</dfn></dt>
+ <dd>
+ A list of all nodes in the <a class="tref internalDFN" title="input_graph" href="#dfn-input_graph">input graph</a>.
+ </dd>
+ <dt><dfn title="alpha" id="dfn-alpha">alpha</dfn> and <dfn title="beta" id="dfn-beta">beta</dfn> values</dt>
+ <dd>
+ The words <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> and <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a> refer to the first and
+ second nodes or values being examined in an algorithm. The names are
+ merely used to refer to each input value to a comparison algorithm.
+ </dd>
+ <dt><dfn title="renaming_counter" id="dfn-renaming_counter">renaming counter</dfn></dt>
+ <dd>
+ A counter that is used during the
+ <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>. The
+ counter typically starts at one (1) and counts up for every node that is
+ relabeled. There will be two such renaming counters in an implementation
+ of the normalization algorithm. The first is the
+ <a class="tref internalDFN" title="labeling_counter" href="#dfn-labeling_counter">labeling counter</a> and the second is the
+ <a class="tref" title="deterministic_labeling_counter">deterministic labeling counter</a>.
+ </dd>
+ <dt><dfn title="serialization_label" id="dfn-serialization_label">serialization label</dfn></dt>
+ <dd>
+ An identifier that is created to aid in the normalization process in the
+ <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a>. The
+ value typically takes the form of <code>s<NUMBER></code> or
+ <code>c<NUMBER></code>.
+ </dd>
+</dl>
+</div>
+
+<div id="normalization-state" class="section">
+<h3><span class="secno">2.2 </span>Normalization State</h3>
+
+<p>When performing the steps required by the normalization algorithm,
+it is helpful to track the many pieces of information in a
+data structure called the <dfn title="normalization_state" id="dfn-normalization_state">normalization state</dfn>. Many of these
+pieces simply provide indexes into the graph. The information
+contained in the <a class="tref internalDFN" title="normalization_state" href="#dfn-normalization_state">normalization state</a> is described below.</p>
+
+<dl>
+ <dt><dfn title="node_state" id="dfn-node_state">node state</dfn></dt>
+ <dd>
+ Each node in the graph will be assigned a <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>. This
+ state contains the information necessary to deterministically
+ <a class="tref internalDFN" title="label" href="#dfn-label">label</a> all nodes in the graph. A <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>
+ includes:
+ <dl>
+ <dt><dfn title="node_reference" id="dfn-node_reference">node reference</dfn></dt>
+ <dd>
+ A <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a> is a reference to a node in the graph.
+ For a given <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, its <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>
+ refers to the node that the state is for. When a
+ <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a> is created, its <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>
+ should be to the node it is created for.
+ </dd>
+ <dt><dfn title="outgoing_list" id="dfn-outgoing_list">outgoing list</dfn></dt>
+ <dd>
+ Lists the <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s for all nodes that are properties of
+ the <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>. This list should be initialized
+ by iterating over every object associated with a property in the
+ <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a> adding its label if it is another node.
+ </dd>
+ <dt><dfn title="incoming_list" id="dfn-incoming_list">incoming list</dfn></dt>
+ <dd>
+ Lists the <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s for all nodes in the graph for which
+ the <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a> is a property. This list is
+ initialized to an empty list.
+ </dd>
+ <dt><dfn title="outgoing_serialization_map" id="dfn-outgoing_serialization_map">outgoing serialization map</dfn></dt>
+ <dd>
+ Maps node <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s to <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>s.
+ This map is initialized to an empty map. When this map is populated,
+ it will be filled with keys that are the <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s of every node in the
+ graph with a label that begins with <code>_:</code> and that has a
+ path, via properties, that starts with the
+ <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>.
+ </dd>
+ <dt><dfn title="outgoing_serialization" id="dfn-outgoing_serialization">outgoing serialization</dfn></dt>
+ <dd>
+ A string that can be lexicographically compared to the
+ <a class="tref internalDFN" title="outgoing_serialization" href="#dfn-outgoing_serialization">outgoing serialization</a>s of other
+ <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>s. It is a representation of the
+ <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a> and other related
+ information. This string is initialized to an empty string.
+ </dd>
+ <dt><dfn title="incoming_serialization_map" id="dfn-incoming_serialization_map">incoming serialization map</dfn></dt>
+ <dd>
+ Maps node <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s to <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>s.
+ This map is initialized to an empty map. When this map is populated,
+ it will be filled with keys that are the <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s of every
+ node in the graph with a <a class="tref internalDFN" title="label" href="#dfn-label">label</a> that begins with
+ <code>_:</code> and that has a path, via properties, that ends with
+ the <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>.
+ </dd>
+ <dt><dfn title="incoming_serialization" id="dfn-incoming_serialization">incoming serialization</dfn></dt>
+ <dd>
+ A string that can be lexicographically compared to the
+ <a class="tref internalDFN" title="outgoing_serialization" href="#dfn-outgoing_serialization">outgoing serialization</a>s of other
+ <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>s. It is a representation of the
+ <a class="tref internalDFN" title="incoming_serialization_map" href="#dfn-incoming_serialization_map">incoming serialization map</a> and other related
+ information. This string is initialized to an empty string.
+ </dd>
+ </dl>
+ </dd>
+ <dt><dfn title="node_state_map" id="dfn-node_state_map">node state map</dfn></dt>
+ <dd>
+ A mapping from a node's <a class="tref internalDFN" title="label" href="#dfn-label">label</a> to a <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>.
+ It is initialized to an empty map.
+ </dd>
+ <dt><dfn title="labeling_prefix" id="dfn-labeling_prefix">labeling prefix</dfn></dt>
+ <dd>
+ The labeling prefix is a string that is used as the beginning of a node
+ <a class="tref internalDFN" title="label" href="#dfn-label">label</a>. It should be initialized to a random base string that
+ starts with the characters <code>_:</code>, is not used by any other
+ node's <a class="tref internalDFN" title="label" href="#dfn-label">label</a> in the <a class="tref internalDFN" title="input_graph" href="#dfn-input_graph">input graph</a>, and does not
+ start with the characters <code>_:c14n</code>. The prefix has two uses.
+ First it is used to temporarily name nodes during the normalization
+ algorithm in a way that doesn't collide with the names that already
+ exist as well as the names that will be generated by the normalization
+ algorithm. Second, it will eventually be set to <code>_:c14n</code> to
+ generate the final, deterministic labels for nodes in the graph. This
+ prefix will be concatenated with the <a class="tref internalDFN" title="labeling_counter" href="#dfn-labeling_counter">labeling counter</a> to
+ produce a node <a class="tref internalDFN" title="label" href="#dfn-label">label</a>. For example, <code>_:j8r3k</code> is
+ a proper initial value for the <a class="tref internalDFN" title="labeling_prefix" href="#dfn-labeling_prefix">labeling prefix</a>.
+ </dd>
+ <dt><dfn title="labeling_counter" id="dfn-labeling_counter">labeling counter</dfn></dt>
+ <dd>
+ A counter that is used to label nodes. It is appended to the
+ <a class="tref internalDFN" title="labeling_prefix" href="#dfn-labeling_prefix">labeling prefix</a> to create a node <a class="tref internalDFN" title="label" href="#dfn-label">label</a>. It is
+ initialized to <code>1</code>.
+ </dd>
+ <dt><dfn title="map_of_flattened_nodes" id="dfn-map_of_flattened_nodes">map of flattened nodes</dfn></dt>
+ <dd>
+ A map containing a representation of all nodes in the graph where the
+ key is a node <a class="tref internalDFN" title="label" href="#dfn-label">label</a> and the value is a single
+ <a class="tref" title="JSON_object">JSON object</a> that has no nested sub-objects
+ and has had all properties for the same node merged into a single
+ <a class="tref" title="JSON_object">JSON object</a>.
+ </dd>
+</dl>
+
+</div>
+
+<div id="normalization-algorithm" class="section">
+<h3><span class="secno">2.3 </span>Normalization Algorithm</h3>
+
+<p>The normalization algorithm expands the <a class="tref internalDFN" title="input_graph" href="#dfn-input_graph">input graph</a>,
+flattens the data structure, and creates an initial set of names for all
+nodes in the graph. The flattened data structure is then processed by a
+node labeling algorithm in order to get a fully expanded and named list of
+nodes which is then sorted. The result is a deterministically named and
+ordered list of graph nodes.
+</p>
+
+<ol class="algorithm">
+<li>Expand the <a class="tref internalDFN" title="input_graph" href="#dfn-input_graph">input graph</a> according to the steps in
+the <a href="#expansion-algorithm">Expansion Algorithm</a> and store the
+result as the <strong>expanded input</strong>.</li>
+<li>Create a <a class="tref internalDFN" title="normalization_state" href="#dfn-normalization_state">normalization state</a>.</li>
+<li>Initialize the <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a> by recursively
+processing every <dfn title="expanded_node" id="dfn-expanded_node">expanded node</dfn> in the
+<strong>expanded input</strong> in depth-first order:
+ <ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a> is an unlabeled node, add a
+ new key-value pair to the <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a>
+ where the key is <code>@subject</code> and the value is the
+ concatenation of the <a class="tref internalDFN" title="labeling_prefix" href="#dfn-labeling_prefix">labeling prefix</a>
+ and the string value of the <a class="tref internalDFN" title="labeling_counter" href="#dfn-labeling_counter">labeling counter</a>.
+ Increment the <a class="tref internalDFN" title="labeling_counter" href="#dfn-labeling_counter">labeling counter</a>.</li>
+ <li>Add the <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a> to the
+ <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a>:
+ <ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a>'s <a class="tref internalDFN" title="label" href="#dfn-label">label</a> is already
+ in the
+ <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a> merge all properties from the
+ entry in the <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a> into the
+ <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a>.</li>
+ <li>Go through every property associated with an array in the
+ <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a> and remove any duplicate IRI entries from
+ the array. If the resulting array only has one IRI entry, change it
+ from an array to an object.</li>
+ <li>Set the entry for the <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a>'s <a class="tref internalDFN" title="label" href="#dfn-label">label</a>
+ in the <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a> to the
+ <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a>.
+ </li></ol></li>
+ <li>After exiting the recursive step, replace the reference to the
+ <a class="tref internalDFN" title="expanded_node" href="#dfn-expanded_node">expanded node</a> with an object containing a single
+ key-value pair where the key is <code>@iri</code> and the value is
+ the value of the <code>@subject</code> key in the node.</li>
+ </ol></li>
+<li>For every entry in the <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a>, insert a
+ key-value pair into the <a class="tref internalDFN" title="node_state_map" href="#dfn-node_state_map">node state map</a> where the key is the
+ key from the <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a> and the value is a
+ <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a> where its <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a> refers to
+ the value from the <a class="tref internalDFN" title="map_of_flattened_nodes" href="#dfn-map_of_flattened_nodes">map of flattened nodes</a>.
+</li><li>Populate the <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a> for each <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>
+ by iterating over every node in the graph and adding its <a class="tref internalDFN" title="label" href="#dfn-label">label</a>
+ to the <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a> associated with each node found in its
+ properties.</li>
+<li>For every entry in the <a class="tref internalDFN" title="node_state_map" href="#dfn-node_state_map">node state map</a> that has a
+<a class="tref internalDFN" title="label" href="#dfn-label">label</a> that begins with <code>_:c14n</code>, relabel the node
+using the <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>.
+</li><li>Label all of the nodes that contain a <code>@subject</code> key associated
+with a value starting with <code>_:</code> according to the steps in the
+<a href="#deterministic-labeling-algorithm">Deterministic Labeling Algorithm</a>.
+</li>
+</ol>
+</div>
+
+<div id="node-relabeling-algorithm" class="section">
+<h3><span class="secno">2.4 </span>Node Relabeling Algorithm</h3>
+
+<p>This algorithm renames a node by generating a unique
+<dfn title="new_label" id="dfn-new_label">new label</dfn> and updating all references to that <a class="tref internalDFN" title="label" href="#dfn-label">label</a>
+in the <a class="tref internalDFN" title="node_state_map" href="#dfn-node_state_map">node state map</a>. The <dfn title="old_label" id="dfn-old_label">old label</dfn> and the
+<a class="tref internalDFN" title="normalization_state" href="#dfn-normalization_state">normalization state</a> must be given as an input to the
+algorithm. The <a class="tref internalDFN" title="old_label" href="#dfn-old_label">old label</a> is the current <a class="tref internalDFN" title="label" href="#dfn-label">label</a> of
+the node that is to be relabeled.
+
+</p><p>The node relabeling algorithm is as follows:</p>
+
+<ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="labeling_prefix" href="#dfn-labeling_prefix">labeling prefix</a> is <code>_:c14n</code> and the
+ <a class="tref internalDFN" title="old_label" href="#dfn-old_label">old label</a> begins with <code>_:c14n</code> then return as
+ the node has already been renamed.
+ </li>
+ <li>Generate the <dfn title="new_label" id="dfn-new_label-1">new label</dfn> by concatenating the
+ <a class="tref internalDFN" title="labeling_prefix" href="#dfn-labeling_prefix">labeling prefix</a> with the string value of the
+ <a class="tref internalDFN" title="labeling_counter" href="#dfn-labeling_counter">labeling counter</a>. Increment the <a class="tref internalDFN" title="labeling_counter" href="#dfn-labeling_counter">labeling counter</a>.
+ </li>
+ <li>For the <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a> associated with the
+ <a class="tref internalDFN" title="old_label" href="#dfn-old_label">old label</a>, update every node in the <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a>
+ by changing all the properties that reference the <a class="tref internalDFN" title="old_label" href="#dfn-old_label">old label</a> to
+ the <a class="tref internalDFN" title="new_label" href="#dfn-new_label-1">new label</a>.
+ </li>
+ <li>Change the <a class="tref internalDFN" title="old_label" href="#dfn-old_label">old label</a> key in the <a class="tref internalDFN" title="node_state_map" href="#dfn-node_state_map">node state map</a>
+ to the <a class="tref internalDFN" title="new_label" href="#dfn-new_label-1">new label</a> and set the associated
+ <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>'s <a class="tref internalDFN" title="label" href="#dfn-label">label</a> to the
+ <a class="tref internalDFN" title="new_label" href="#dfn-new_label-1">new label</a>.
+ </li>
+</ol>
+</div>
+
+<div id="deterministic-labeling-algorithm" class="section">
+<h3><span class="secno">2.5 </span>Deterministic Labeling Algorithm</h3>
+
+<p>The deterministic labeling algorithm takes the
+<a class="tref internalDFN" title="normalization_state" href="#dfn-normalization_state">normalization state</a>
+and produces a <dfn title="list_of_finished_nodes" id="dfn-list_of_finished_nodes">list of finished nodes</dfn> that is sorted and
+contains deterministically named and expanded nodes from the graph.
+
+</p><ol class="algorithm">
+ <li>Set the <a class="tref internalDFN" title="labeling_prefix" href="#dfn-labeling_prefix">labeling prefix</a> to <code>_:c14n</code>, the
+ <a class="tref internalDFN" title="labeling_counter" href="#dfn-labeling_counter">labeling counter</a> to <code>1</code>,
+ the <dfn title="list_of_finished_nodes" id="dfn-list_of_finished_nodes-1">list of finished nodes</dfn> to an empty array, and create
+ an empty array, the <dfn title="list_of_unfinished_nodes" id="dfn-list_of_unfinished_nodes">list of unfinished nodes</dfn>.</li>
+ <li>For each <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a> in the <a class="tref internalDFN" title="node_state_map" href="#dfn-node_state_map">node state map</a>:
+ <ol class="algorithm">
+ <li>If the node's <a class="tref internalDFN" title="label" href="#dfn-label">label</a> does not start with <code>_:</code>
+ then put the <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a> in the
+ <a class="tref internalDFN" title="list_of_finished_nodes" href="#dfn-list_of_finished_nodes-1">list of finished nodes</a>.
+ </li>
+ <li>If the node's <a class="tref internalDFN" title="label" href="#dfn-label">label</a> does start with <code>_:</code>
+ then put the <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a> in the
+ <a class="tref internalDFN" title="list_of_unfinished_nodes" href="#dfn-list_of_unfinished_nodes">list of unfinished nodes</a>.
+ </li>
+ </ol>
+ </li>
+ <li>Append to the <a class="tref internalDFN" title="list_of_finished_nodes" href="#dfn-list_of_finished_nodes-1">list of finished nodes</a> by processing
+ the remainder of the <a class="tref internalDFN" title="list_of_unfinished_nodes" href="#dfn-list_of_unfinished_nodes">list of unfinished nodes</a> until it is
+ empty:
+ <ol class="algorithm">
+ <li>Sort the <a class="tref internalDFN" title="list_of_unfinished_nodes" href="#dfn-list_of_unfinished_nodes">list of unfinished nodes</a> in descending order
+ according to the
+ <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a> to
+ determine the sort order.</li>
+ <li>Create a <dfn title="list_of_labels" id="dfn-list_of_labels">list of labels</dfn> and initialize it to an
+ empty array.</li>
+ <li>For the first node from the <a class="tref internalDFN" title="list_of_unfinished_nodes" href="#dfn-list_of_unfinished_nodes">list of unfinished nodes</a>:
+ <ol class="algorithm">
+ <li>Add its <a class="tref internalDFN" title="label" href="#dfn-label">label</a> to the <a class="tref internalDFN" title="list_of_labels" href="#dfn-list_of_labels">list of labels</a>.
+ </li>
+ <li>For each key-value pair from its associated
+ <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a>, add the key to a list and
+ then sort the list according to the lexicographical order of the
+ keys' associated values. Append the list to the
+ <a class="tref" title="list_of_nodes_to_label">list of nodes to label</a>.
+ </li>
+ <li>For each key-value pair from its associated
+ <a class="tref internalDFN" title="incoming_serialization_map" href="#dfn-incoming_serialization_map">incoming serialization map</a>, add the key to a list and
+ then sort the list according to the lexicographical order of the
+ keys' associated values. Append the list to the
+ <a class="tref" title="list_of_nodes_to_label">list of nodes to label</a>.
+ </li></ol></li>
+ <li>For each <a class="tref internalDFN" title="label" href="#dfn-label">label</a> in the <a class="tref internalDFN" title="list_of_labels" href="#dfn-list_of_labels">list of labels</a>,
+ relabel the associated node according to the
+ <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>. If
+ any <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a> contains a key that
+ matches the <a class="tref internalDFN" title="label" href="#dfn-label">label</a>, clear the map and set the associated
+ <a class="tref internalDFN" title="outgoing_serialization" href="#dfn-outgoing_serialization">outgoing serialization</a> to an empty string. If any
+ <a class="tref internalDFN" title="incoming_serialization_map" href="#dfn-incoming_serialization_map">incoming serialization map</a> contains a key that
+ matches the <a class="tref internalDFN" title="label" href="#dfn-label">label</a>, clear the map and set the associated
+ <a class="tref internalDFN" title="incoming_serialization" href="#dfn-incoming_serialization">incoming serialization</a> to an empty string.
+ </li>
+ <li>
+ Remove each node with a <a class="tref internalDFN" title="label" href="#dfn-label">label</a> that starts with
+ <code>_:c14n</code> from the <a class="tref internalDFN" title="list_of_unfinished_nodes" href="#dfn-list_of_unfinished_nodes">list of unfinished nodes</a> and
+ add it to the <a class="tref internalDFN" title="list_of_finished_nodes" href="#dfn-list_of_finished_nodes-1">list of finished nodes</a>.
+ </li>
+ </ol>
+ </li>
+ <li>Sort the <a class="tref internalDFN" title="list_of_finished_nodes" href="#dfn-list_of_finished_nodes-1">list of finished nodes</a> in descending order
+ according to the
+ <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a> to
+ determine the sort order.</li>
+</ol>
+</div>
+
+<div id="shallow-comparison-algorithm" class="section">
+<h3><span class="secno">2.6 </span>Shallow Comparison Algorithm</h3>
+
+<p>
+The shallow comparison algorithm takes two unlabeled nodes,
+<a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> and <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>, as input and
+determines which one should come first in a sorted list. The following
+algorithm determines the steps that are executed in order to determine the
+node that should come first in a list:
+</p>
+
+<ol class="algorithm">
+ <li>Compare the total number of node properties. The node with fewer
+ properties is first.</li>
+ <li>Lexicographically sort the property IRIs for each node and compare
+ the sorted lists. If an IRI is found to be lexicographically smaller, the
+ node containing that IRI is first.</li>
+ <li>Compare the values of each property against one another:
+ <ol class="algorithm">
+ <li>The node associated with fewer property values is first.
+ </li>
+ <li>Create an <dfn title="alpha_list" id="dfn-alpha_list">alpha list</dfn> by adding all values associated
+ with the <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> property that are not unlabeled nodes.
+ </li>
+ <li>Create a <dfn title="beta_list" id="dfn-beta_list">beta list</dfn> by adding all values associated
+ with the <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a> property that is not an unlabeled node.
+ </li>
+ <li>Compare the length of <a class="tref internalDFN" title="alpha_list" href="#dfn-alpha_list">alpha list</a> and
+ <a class="tref internalDFN" title="beta_list" href="#dfn-beta_list">beta list</a>. The node associated with the list containing
+ the fewer number of items is first.</li>
+ <li>Sort <a class="tref internalDFN" title="alpha_list" href="#dfn-alpha_list">alpha list</a> and <a class="tref internalDFN" title="beta_list" href="#dfn-beta_list">beta list</a> according to
+ the
+ <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>.
+ For each offset into the <a class="tref internalDFN" title="alpha_list" href="#dfn-alpha_list">alpha list</a>, compare the item
+ at the offset against the item at the same offset in the
+ <a class="tref internalDFN" title="beta_list" href="#dfn-beta_list">beta list</a> according to the
+ <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>.
+ The node associated with the lesser item is first.
+ </li></ol></li>
+ <li>Process the <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a>s associated with each node to
+ determine order:
+ <ol class="algorithm">
+ <li>The node with the shortest <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a> is first.</li>
+ <li>Sort the <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a>s according to incoming property
+ and then incoming <a class="tref internalDFN" title="label" href="#dfn-label">label</a>.
+ </li><li>The node associated with the fewest number of incoming nodes is
+ first.</li>
+ <li>For each offset into the <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a>s,
+ compare the associated properties and <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s:
+ <ol class="algorithm">
+ <li>The node associated with a <a class="tref internalDFN" title="label" href="#dfn-label">label</a> that does not begin with
+ <code>_:</code> is first.
+ </li>
+ <li>If the nodes' <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s do not begin with
+ <code>_:</code>, then the node associated with the
+ lexicographically lesser <a class="tref internalDFN" title="label" href="#dfn-label">label</a> is first.</li>
+
+ <li>The node associated with the lexicographically lesser associated
+ property is first.
+ </li>
+ <li>The node with the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> that does not begin with
+ <code>_:c14n</code> is first.
+ </li>
+ <li>The node with the lexicographically lesser <a class="tref internalDFN" title="label" href="#dfn-label">label</a>
+ is first.
+ </li>
+ </ol>
+ </li></ol></li>
+ <li>Otherwise, the nodes are equivalent.</li>
+</ol></div>
+
+<div id="object-comparison-algorithm" class="section">
+<h3><span class="secno">2.7 </span>Object Comparison Algorithm</h3>
+
+<p>
+The object comparison algorithm is designed to compare two graph node
+property values, <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> and <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>, against the other.
+The algorithm is useful when sorting two lists of graph node properties.
+</p>
+
+<ol class="algorithm">
+ <li>If one of the values is a <a class="tref" title="string">string</a> and the other is not, the value that is
+ a string is first.
+ </li>
+ <li>If both values are <a class="tref" title="string">string</a>s, the lexicographically lesser string is
+ first.
+ </li>
+ <li>If one of the values is a literal and the other is not, the value that is
+ a literal is first.
+ </li>
+ <li>If both values are literals:
+ <ol class="algorithm">
+ <li>The lexicographically lesser string associated with
+ <code>@literal</code> is first.
+ </li>
+ <li>The lexicographically lesser string associated with
+ <code>@datatype</code> is first.
+ </li>
+ <li>The lexicographically lesser string associated with
+ <code>@language</code> is first.
+ </li>
+ </ol>
+ </li>
+ <li>If both values are expanded IRIs, the
+ lexicographically lesser string associated with <code>@iri</code>
+ is first.</li>
+ <li>Otherwise, the two values are equivalent.</li>
+</ol>
+
+</div>
+
+<div id="deep-comparison-algorithm" class="section">
+<h3><span class="secno">2.8 </span>Deep Comparison Algorithm</h3>
+
+<p>
+The deep comparison algorithm is used to compare the difference between two
+nodes, <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> and <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>.
+A deep comparison takes the incoming and outgoing node edges in
+a graph into account if the number of properties and value of those properties
+are identical. The algorithm is helpful when sorting a list of nodes and will
+return whichever node should be placed first in a list if the two nodes are
+not truly equivalent.
+</p>
+
+<p>When performing the steps required by the deep comparison algorithm, it
+is helpful to track state information about mappings. The information
+contained in a <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a> is described below.</p>
+
+<dl class="algorithm">
+ <dt><dfn title="mapping_state" id="dfn-mapping_state">mapping state</dfn></dt>
+ <dd>
+ <dl>
+ <dt><dfn title="mapping_counter" id="dfn-mapping_counter">mapping counter</dfn></dt>
+ <dd>
+ Keeps track of the number of nodes that have been mapped to
+ <a class="tref" title="serialization_labels">serialization labels</a>. It is initialized to
+ <code>1</code>.
+ </dd>
+ <dt><dfn title="processed_labels_map" id="dfn-processed_labels_map">processed labels map</dfn></dt>
+ <dd>
+ Keeps track of the <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s of nodes that have already
+ been assigned <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>s. It is initialized
+ to an empty map.
+ </dd>
+ <dt><dfn title="serialized_labels_map" id="dfn-serialized_labels_map">serialized labels map</dfn></dt>
+ <dd>
+ Maps a node <a class="tref internalDFN" title="label" href="#dfn-label">label</a> to its associated
+ <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>. It is initialized to an empty map.
+ </dd>
+ <dt><dfn title="adjacent_info_map" id="dfn-adjacent_info_map">adjacent info map</dfn></dt>
+ <dd>
+ Maps a <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a> to the node
+ <a class="tref internalDFN" title="label" href="#dfn-label">label</a> associated with it, the list of sorted
+ <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>s for adjacent nodes, and the map of
+ adjacent node <a class="tref" title="serialiation_label">serialiation label</a>s to their associated
+ node <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s. It is initialized to an empty map.
+ </dd>
+ <dt><dfn title="key_stack" id="dfn-key_stack">key stack</dfn></dt>
+ <dd>
+ A stack where each element contains an array of adjacent
+ <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>s and an index into that array. It
+ is initialized to a stack containing a single element where its
+ array contains a single string element <code>s1</code> and its
+ index is set to <code>0</code>.
+ </dd>
+ <dt><dfn title="serialized_keys" id="dfn-serialized_keys">serialized keys</dfn></dt>
+ <dd>
+ Keeps track of which <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>s have already
+ been written at least once to the <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a>.
+ It is initialized to an empty map.
+ </dd>
+ <dt><dfn title="serialization_string" id="dfn-serialization_string">serialization string</dfn></dt>
+ <dd>
+ A string that is incrementally updated as a serialization is built.
+ It is initialized to an empty string.
+ </dd>
+ </dl>
+ </dd>
+</dl>
+
+<p>The deep comparison algorithm is as follows:</p>
+
+<ol class="algorithm">
+ <li>Perform a comparison between <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> and <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>
+ according to the
+ <a href="#shallow-comparison-algorithm">Shallow Comparison Algorithm</a>.
+ If the result does not show that the two nodes are equivalent, return
+ the result.
+ </li>
+ <li>Compare incoming and outgoing edges for each node, updating their
+ associated <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a> as each node is processed:
+ <ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a> for <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>'s <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, a new
+ <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a>,
+ <code>outgoing direction</code> to the algorithm as inputs.
+ </li><li>If the <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a> for <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>'s <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, a new
+ <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a>, and
+ <code>outgoing direction</code> to the algorithm as inputs.
+ </li><li>If <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>'s <a class="tref internalDFN" title="outgoing_serialization" href="#dfn-outgoing_serialization">outgoing serialization</a> is
+ lexicographically less than <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>'s, then
+ <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> is first. If it is greater, then <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>
+ is first.</li>
+ <li>If the <a class="tref internalDFN" title="incoming_serialization_map" href="#dfn-incoming_serialization_map">incoming serialization map</a> for <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>'s <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, a new
+ <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a> with its <a class="tref internalDFN" title="serialized_labels_map" href="#dfn-serialized_labels_map">serialized labels map</a>
+ set to a copy of <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>'s
+ <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a>, and
+ <code>incoming direction</code> to the algorithm as inputs.
+ </li><li>If the <a class="tref internalDFN" title="incoming_serialization_map" href="#dfn-incoming_serialization_map">incoming serialization map</a> for <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>'s <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, a new
+ <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a> with its <a class="tref internalDFN" title="serialized_labels_map" href="#dfn-serialized_labels_map">serialized labels map</a>
+ set to a copy of <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>'s
+ <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a>, and
+ <code>incoming direction</code> to the algorithm as inputs.
+ </li><li>If <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>'s <a class="tref internalDFN" title="incoming_serialization" href="#dfn-incoming_serialization">incoming serialization</a> is
+ lexicographically less than <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>'s, then
+ <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> is first. If it is greater, then <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a>
+ is first.</li>
+ </ol></li>
+</ol>
+</div>
+
+<div id="node-serialization-algorithm" class="section">
+<h3><span class="secno">2.9 </span>Node Serialization Algorithm</h3>
+
+<p>
+The node serialization algorithm takes a <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, a
+<a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a>, and a <dfn title="direction" id="dfn-direction">direction</dfn> (either
+<code>outgoing direction</code> or <code>incoming direction</code>) as
+inputs and generates a deterministic serialization for the
+<a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>.
+</p>
+
+<ol class="algorithm">
+<li>If the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> exists in the
+ <a class="tref internalDFN" title="processed_labels_map" href="#dfn-processed_labels_map">processed labels map</a>, terminate the algorithm as the
+ <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a> has already been created.
+</li>
+<li>Set the value associated with the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> in the
+ <a class="tref internalDFN" title="processed_labels_map" href="#dfn-processed_labels_map">processed labels map</a> to <code>true</code>.
+</li>
+<li>Generate the next <dfn title="serialization_label" id="dfn-serialization_label-1">serialization label</dfn> for the
+ <a class="tref internalDFN" title="label" href="#dfn-label">label</a> according to the
+ <a href="#serialization-label-generation-algorithm">Serialization Label Generation Algorithm</a>.
+</li>
+<li>Create an empty map called the <dfn title="adjacent_serialized_labels_map" id="dfn-adjacent_serialized_labels_map">adjacent serialized labels map</dfn>
+that will store mappings from <a class="tref" title="serialized_label">serialized label</a>s to adjacent
+node <a class="tref internalDFN" title="label" href="#dfn-label">label</a>s.</li>
+<li>Create an empty array called the
+<dfn title="adjacent_unserialized_labels_list" id="dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</dfn> that will store
+<a class="tref internalDFN" title="label" href="#dfn-label">label</a>s of adjacent nodes that haven't been assigned
+<a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>s yet.
+</li>
+<li>For every <a class="tref internalDFN" title="label" href="#dfn-label">label</a> in a list, where the list the <a class="tref internalDFN" title="outgoing_list" href="#dfn-outgoing_list">outgoing list</a> if
+the <a class="tref internalDFN" title="direction" href="#dfn-direction">direction</a> is <code>outgoing direction</code> and the
+<a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a> otherwise, if the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> starts with
+<code>_:</code>, it is the <dfn title="target_node_label" id="dfn-target_node_label">target node label</dfn>:
+ <ol class="algorithm">
+ <li>Look up the <a class="tref internalDFN" title="target_node_label" href="#dfn-target_node_label">target node label</a> in the
+ <a class="tref internalDFN" title="processed_labels_map" href="#dfn-processed_labels_map">processed labels map</a> and if a mapping exists,
+ update the <a class="tref internalDFN" title="adjacent_serialized_labels_map" href="#dfn-adjacent_serialized_labels_map">adjacent serialized labels map</a> where the key is
+ the value in the <a class="tref" title="serialization_map">serialization map</a> and the value is the
+ <a class="tref internalDFN" title="target_node_label" href="#dfn-target_node_label">target node label</a>.</li>
+ <li>Otherwise, add the <a class="tref internalDFN" title="target_node_label" href="#dfn-target_node_label">target node label</a> to the
+ <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a>.
+ </li></ol>
+</li>
+<li>Set the <dfn title="maximum_serialization_combinations" id="dfn-maximum_serialization_combinations">maximum serialization combinations</dfn> to
+ <code>1</code> or the length of the
+ <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a>, whichever is greater.</li>
+<li>While the <a class="tref internalDFN" title="maximum_serialization_combinations" href="#dfn-maximum_serialization_combinations">maximum serialization combinations</a> is greater than
+ <code>0</code>, perform the
+ <a href="#combinatorial-serialization-algorithm">Combinatorial Serialization Algorithm</a>
+ passing the <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, the <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a> for the
+ first iteration and a copy of it for each subsequent iteration, the
+ generated <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>, the <a class="tref internalDFN" title="direction" href="#dfn-direction">direction</a>,
+ the <a class="tref internalDFN" title="adjacent_serialized_labels_map" href="#dfn-adjacent_serialized_labels_map">adjacent serialized labels map</a>, and the
+ <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a>.
+ Decrement the <a class="tref internalDFN" title="maximum_serialization_combinations" href="#dfn-maximum_serialization_combinations">maximum serialization combinations</a> by
+ <code>1</code> for each iteration.
+</li></ol>
+
+</div>
+
+<div id="serialization-label-generation-algorithm" class="section">
+<h3><span class="secno">2.10 </span>Serialization Label Generation Algorithm</h3>
+
+<p>
+The algorithm generates a <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a> given a
+<a class="tref internalDFN" title="label" href="#dfn-label">label</a> and a <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a> and returns the
+<a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>.
+</p>
+
+ <ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> is already in the
+ <a class="tref" title="serialization_labels_map">serialization labels map</a>, return its associated value.
+ </li>
+ <li>If the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> starts with the string <code>_:c14n</code>,
+ the <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a> is the letter <code>c</code>
+ followed by the number that follows <code>_:c14n</code> in the
+ <a class="tref internalDFN" title="label" href="#dfn-label">label</a>.
+ </li>
+ <li>Otherwise, the <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a> is the
+ letter <code>s</code> followed by the string value of
+ <a class="tref" title="mapping_count">mapping count</a>. Increment the <a class="tref" title="mapping_count">mapping count</a> by
+ <code>1</code>.
+ </li>
+ <li>Create a new key-value pair in the <a class="tref" title="serialization_labels_map">serialization labels map</a>
+ where the key is the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> and the value is the
+ generated <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>.
+ </li>
+ </ol>
+</div>
+
+<div id="combinatorial-serialization-algorithm" class="section">
+<h3><span class="secno">2.11 </span>Combinatorial Serialization Algorithm</h3>
+
+<p>
+The combinatorial serialization algorithm takes a <a class="tref internalDFN" title="node_state" href="#dfn-node_state">node state</a>, a
+<a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a>, a <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>, a
+<a class="tref internalDFN" title="direction" href="#dfn-direction">direction</a>, a <a class="tref internalDFN" title="adjacent_serialized_labels_map" href="#dfn-adjacent_serialized_labels_map">adjacent serialized labels map</a>,
+and a <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a> as inputs and generates
+the lexicographically least serialization of nodes relating to the
+<a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>.
+</p>
+
+<ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a> is not empty:
+ <ol class="algorithm">
+ <li>Copy the <a class="tref internalDFN" title="adjacent_serialized_labels_map" href="#dfn-adjacent_serialized_labels_map">adjacent serialized labels map</a> to the
+ <dfn title="adjacent_serialized_labels_map_copy" id="dfn-adjacent_serialized_labels_map_copy">adjacent serialized labels map copy</dfn>.</li>
+ <li>Remove the first <a class="tref" title="unserialized_label">unserialized label</a> from the
+ <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a> and create a new
+ <dfn title="new_serialization_label" id="dfn-new_serialization_label">new serialization label</dfn> according to the
+ <a href="#serialization-label-generation-algorithm">Serialization Label Generation Algorithm</a>.
+ </li><li>Create a new key-value mapping in the
+ <a class="tref internalDFN" title="adjacent_serialized_labels_map_copy" href="#dfn-adjacent_serialized_labels_map_copy">adjacent serialized labels map copy</a>
+ where the key is the <a class="tref internalDFN" title="new_serialization_label" href="#dfn-new_serialization_label">new serialization label</a> and the value
+ is the <a class="tref" title="unserialized_label">unserialized label</a>.
+ </li><li>Set the <dfn title="maximum_serialization_rotations" id="dfn-maximum_serialization_rotations">maximum serialization rotations</dfn> to
+ <code>1</code> or the length of the
+ <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a>, whichever is greater.
+ </li>
+ <li>While the <a class="tref internalDFN" title="maximum_serialization_rotations" href="#dfn-maximum_serialization_rotations">maximum serialization rotations</a> is greater than
+ <code>0</code>:
+ <ol class="algorithm">
+ <li>Recursively perform the
+ <a href="#combinatorial-serialization-algorithm">Combinatorial Serialization Algorithm</a>
+ passing the <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a> for the first iteration of the
+ loop, and a copy of it for each subsequent iteration.
+ </li>
+ <li>Rotate the elements in the
+ <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a> by shifting each of
+ them once to the right, moving the element at the end of the list
+ to the beginning of the list.
+ </li>
+ <li>Decrement the <a class="tref internalDFN" title="maximum_serialization_rotations" href="#dfn-maximum_serialization_rotations">maximum serialization rotations</a> by
+ <code>1</code> for each iteration.
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ <li>If the <a class="tref internalDFN" title="adjacent_unserialized_labels_list" href="#dfn-adjacent_unserialized_labels_list">adjacent unserialized labels list</a> is empty:
+ <ol class="algorithm">
+ <li>Create a <dfn title="list_of_keys" id="dfn-list_of_keys">list of keys</dfn> from the keys in the
+ <a class="tref internalDFN" title="adjacent_serialized_labels_map" href="#dfn-adjacent_serialized_labels_map">adjacent serialized labels map</a> and sort it
+ lexicographically.
+ </li>
+ <li>Add a key-value pair to the <a class="tref internalDFN" title="adjacent_info_map" href="#dfn-adjacent_info_map">adjacent info map</a> where
+ the key is the <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a> and the value is
+ an object containing the <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>'s label, the
+ <a class="tref internalDFN" title="list_of_keys" href="#dfn-list_of_keys">list of keys</a> and the
+ <a class="tref internalDFN" title="adjacent_serialized_labels_map" href="#dfn-adjacent_serialized_labels_map">adjacent serialized labels map</a>.
+ </li>
+ <li>Update the <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> according to the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
+ </li>
+ <li>If the <a class="tref internalDFN" title="direction" href="#dfn-direction">direction</a> is <code>outgoing direction</code>
+ then <dfn title="directed_serialization" id="dfn-directed_serialization">directed serialization</dfn> refers to the
+ <a class="tref internalDFN" title="outgoing_serialization" href="#dfn-outgoing_serialization">outgoing serialization</a> and the
+ <dfn title="directed_serialization_map" id="dfn-directed_serialization_map">directed serialization map</dfn> refers to the
+ <a class="tref internalDFN" title="outgoing_serialization_map" href="#dfn-outgoing_serialization_map">outgoing serialization map</a>, otherwise it refers to the
+ <a class="tref internalDFN" title="incoming_serialization" href="#dfn-incoming_serialization">incoming serialization</a> and the
+ <a class="tref internalDFN" title="directed_serialization_map" href="#dfn-directed_serialization_map">directed serialization map</a> refers to the
+ <a class="tref internalDFN" title="incoming_serialization_map" href="#dfn-incoming_serialization_map">incoming serialization map</a>. Compare the
+ <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> to the
+ <a class="tref internalDFN" title="directed_serialization" href="#dfn-directed_serialization">directed serialization</a> according to the
+ <a href="#mapping-serialization-algorithm">Serialization Comparison Algorithm</a>.
+ If the <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> is less than or equal to
+ the <a class="tref internalDFN" title="directed_serialization" href="#dfn-directed_serialization">directed serialization</a>:
+ <ol class="algorithm">
+ <li>For each value in the <a class="tref internalDFN" title="list_of_keys" href="#dfn-list_of_keys">list of keys</a>, run the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ </li>
+ <li>Update the <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> according to the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
+ </li>
+ <li>Compare the <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> to the
+ <a class="tref internalDFN" title="directed_serialization" href="#dfn-directed_serialization">directed serialization</a> again and if it is less than
+ or equal and the length of the <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> is
+ greater than or equal to the length of the
+ <a class="tref internalDFN" title="directed_serialization" href="#dfn-directed_serialization">directed serialization</a>, then set the
+ <a class="tref internalDFN" title="directed_serialization" href="#dfn-directed_serialization">directed serialization</a> to the
+ <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> and set the
+ <a class="tref internalDFN" title="directed_serialization_map" href="#dfn-directed_serialization_map">directed serialization map</a> to the
+ <a class="tref internalDFN" title="serialized_labels_map" href="#dfn-serialized_labels_map">serialized labels map</a>.
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+</ol>
+
+</div>
+
+<div id="serialization-comparison-algorithm" class="section">
+<h3><span class="secno">2.12 </span>Serialization Comparison Algorithm</h3>
+
+<p>
+The serialization comparison algorithm takes two serializations,
+<a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a> and <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a> and returns either which of the two
+is less than the other or that they are equal.
+</p>
+
+<ol class="algorithm">
+ <li>Whichever serialization is an empty string is greater. If they are
+ both empty strings, they are equal.</li>
+ <li>Return the result of a lexicographical comparison of <a class="tref internalDFN" title="alpha" href="#dfn-alpha">alpha</a>
+ and <a class="tref internalDFN" title="beta" href="#dfn-beta">beta</a> up to the number of characters in the shortest of
+ the two serializations.
+ </li>
+</ol>
+</div>
+
+<div id="mapping-serialization-algorithm" class="section">
+<h3><span class="secno">2.13 </span>Mapping Serialization Algorithm</h3>
+
+<p>
+The mapping serialization algorithm incrementally updates the
+<a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a> in a <a class="tref internalDFN" title="mapping_state" href="#dfn-mapping_state">mapping state</a>.
+</p>
+
+<ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="key_stack" href="#dfn-key_stack">key stack</a> is not empty:
+ <ol class="algorithm">
+ <li>Pop the <dfn title="serialization_key_info" id="dfn-serialization_key_info">serialization key info</dfn> off of the
+ <a class="tref internalDFN" title="key_stack" href="#dfn-key_stack">key stack</a>.
+ </li>
+ <li>For each <dfn title="serialization_key" id="dfn-serialization_key">serialization key</dfn> in the
+ <a class="tref internalDFN" title="serialization_key_info" href="#dfn-serialization_key_info">serialization key info</a> array, starting at
+ the <dfn title="serialization_key_index" id="dfn-serialization_key_index">serialization key index</dfn> from the
+ <a class="tref internalDFN" title="serialization_key_info" href="#dfn-serialization_key_info">serialization key info</a>:
+ <ol class="algorithm">
+ <li>If the <a class="tref internalDFN" title="serialization_key" href="#dfn-serialization_key">serialization key</a> is not in the
+ <a class="tref internalDFN" title="adjacent_info_map" href="#dfn-adjacent_info_map">adjacent info map</a>, push the
+ <a class="tref internalDFN" title="serialization_key_info" href="#dfn-serialization_key_info">serialization key info</a> onto the
+ <a class="tref internalDFN" title="key_stack" href="#dfn-key_stack">key stack</a> and exit from this loop.
+ </li>
+ <li>If the <a class="tref internalDFN" title="serialization_key" href="#dfn-serialization_key">serialization key</a> is a key in
+ <a class="tref internalDFN" title="serialized_keys" href="#dfn-serialized_keys">serialized keys</a>, a cycle has been detected. Append
+ the concatenation of the <code>_</code> character and the
+ <a class="tref internalDFN" title="serialization_key" href="#dfn-serialization_key">serialization key</a> to the
+ <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a>.
+ </li><li>Otherwise, serialize all outgoing and incoming edges in the
+ related node by performing the following steps:
+ <ol class="algorithm">
+ <li>Mark the <a class="tref internalDFN" title="serialization_key" href="#dfn-serialization_key">serialization key</a> as having
+ been processed by adding a new key-value pair to
+ <a class="tref internalDFN" title="serialized_keys" href="#dfn-serialized_keys">serialized keys</a> where the key
+ is the <a class="tref internalDFN" title="serialization_key" href="#dfn-serialization_key">serialization key</a> and the value is
+ <code>true</code>.
+ </li>
+ <li>Set the <dfn title="serialization_fragment" id="dfn-serialization_fragment">serialization fragment</dfn> to the value of
+ the <a class="tref internalDFN" title="serialization_key" href="#dfn-serialization_key">serialization key</a>.</li>
+ <li>Set the <a class="tref" title="adjacent_info">adjacent info</a> to the value of the
+ <a class="tref internalDFN" title="serialization_key" href="#dfn-serialization_key">serialization key</a> in the
+ <a class="tref internalDFN" title="adjacent_info_map" href="#dfn-adjacent_info_map">adjacent info map</a>.
+ </li>
+ <li>Set the <a class="tref" title="adjacent_node_label">adjacent node label</a> to the node
+ <a class="tref internalDFN" title="label" href="#dfn-label">label</a> from the <a class="tref" title="adjacent_info">adjacent info</a>.
+ </li>
+ <li>If a mapping for the <a class="tref" title="adjacent_node_label">adjacent node label</a>
+ exists in the <a class="tref" title="map_of_all_labels">map of all labels</a>:
+ <ol class="algorithm">
+ <li>Append the result of the
+ <a href="">Label Serialization Algorithm</a> to the
+ <a class="tref internalDFN" title="serialization_fragment" href="#dfn-serialization_fragment">serialization fragment</a>.
+ </li>
+ </ol>
+ </li>
+ <li>Append all of the keys in the <a class="tref" title="adjacent_info">adjacent info</a>
+ to the <a class="tref internalDFN" title="serialization_fragment" href="#dfn-serialization_fragment">serialization fragment</a>.
+ </li>
+ <li>Append the <a class="tref internalDFN" title="serialization_fragment" href="#dfn-serialization_fragment">serialization fragment</a> to the
+ <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a>.
+ </li>
+ <li>Push a new key info object containing the keys from the
+ <a class="tref" title="adjacent_info">adjacent info</a> and an index of <code>0</code>
+ onto the <a class="tref internalDFN" title="key_stack" href="#dfn-key_stack">key stack</a>.
+ </li>
+ <li>Recursively update the <a class="tref internalDFN" title="serialization_string" href="#dfn-serialization_string">serialization string</a>
+ according to the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+</ol>
+
+</div>
+
+<div id="label-serialization-algorithm" class="section">
+<h3><span class="secno">2.14 </span>Label Serialization Algorithm</h3>
+
+<p>
+The label serialization algorithm serializes information about a node that
+has been assigned a particular <a class="tref internalDFN" title="serialization_label" href="#dfn-serialization_label-1">serialization label</a>.
+</p>
+
+<ol class="algorithm">
+ <li>Initialize the <a class="tref" title="label_serialization">label serialization</a> to an empty string.</li>
+ <li>Append the <code>[</code> character to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>Append all properties to the <a class="tref" title="label_serialization">label serialization</a> by
+ processing each key-value pair in the <a class="tref internalDFN" title="node_reference" href="#dfn-node_reference">node reference</a>,
+ excluding the
+ <code>@subject</code> property. The keys should be processed in
+ lexicographical order and their associated values should be processed
+ in the order produced by the
+ <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>:
+ <ol class="algorithm">
+ <li>Build a string using the pattern <code><</code><strong>KEY</strong><code>></code>
+ where <strong>KEY</strong> is the current key. Append string to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>The value may be a single object or an array of objects.
+ Process all of the objects that are associated with the key, building
+ an <dfn title="object_string" id="dfn-object_string">object string</dfn> for each item:
+ <ol class="algorithm">
+ <li>If the object contains an <code>@iri</code> key with a
+ value that starts
+ with <code>_:</code>, set the <a class="tref internalDFN" title="object_string" href="#dfn-object_string">object string</a> to
+ the value <code>_:</code>. If the value does not
+ start with <code>_:</code>, build the <a class="tref internalDFN" title="object_string" href="#dfn-object_string">object string</a>
+ using the pattern
+ <code><</code><strong>IRI</strong><code>></code>
+ where <strong>IRI</strong> is the value associated with the
+ <code>@iri</code> key.</li>
+ <li>If the object contains a <code>@literal</code> key and a
+ <code>@datatype</code> key, build the <a class="tref internalDFN" title="object_string" href="#dfn-object_string">object string</a>
+ using the pattern
+ <code>"</code><strong>LITERAL</strong><code>"^^<</code><strong>DATATYPE</strong><code>></code>
+ where <strong>LITERAL</strong> is the value associated with the
+ <code>@literal</code> key and <strong>DATATYPE</strong> is the
+ value associated with the <code>@datatype</code> key.</li>
+ <li>If the object contains a <code>@literal</code> key and a
+ <code>@language</code> key, build the <a class="tref internalDFN" title="object_string" href="#dfn-object_string">object string</a>
+ using the pattern
+ <code>"</code><strong>LITERAL</strong><code>"@</code><strong>LANGUAGE</strong>
+ where <strong>LITERAL</strong> is the value associated with the
+ <code>@literal</code> key and <strong>LANGUAGE</strong> is the
+ value associated with the <code>@language</code> key.</li>
+ <li>Otherwise, the value is a string. Build the
+ <a class="tref internalDFN" title="object_string" href="#dfn-object_string">object string</a> using the pattern
+ <code>"</code><strong>LITERAL</strong><code>"</code>
+ where <strong>LITERAL</strong> is the value associated with the
+ current key.</li>
+ <li>If this is the second iteration of the loop,
+ append a <code>|</code> separator character to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>Append the <a class="tref internalDFN" title="object_string" href="#dfn-object_string">object string</a> to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ </ol>
+ </li></ol>
+ </li>
+ <li>Append the <code>]</code> character to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>Append the <code>[</code> character to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>Append all incoming references for the current
+ <a class="tref internalDFN" title="label" href="#dfn-label">label</a> to the <a class="tref" title="label_serialization">label serialization</a> by
+ processing all of the items associated with the <a class="tref internalDFN" title="incoming_list" href="#dfn-incoming_list">incoming list</a>:
+ <ol class="algorithm">
+ <li>Build a <dfn title="reference_string" id="dfn-reference_string">reference string</dfn>
+ using the pattern <code><</code><strong>PROPERTY</strong><code>></code><code><</code><strong>REFERER</strong><code>></code>
+ where <strong>PROPERTY</strong> is the property associated with the
+ incoming reference and <strong>REFERER</strong> is either the subject of
+ the node referring to the <a class="tref internalDFN" title="label" href="#dfn-label">label</a> in the incoming reference
+ or <code>_:</code> if <strong>REFERER</strong> begins with
+ <code>_:</code>.
+ </li><li>If this is the second iteration of the loop,
+ append a <code>|</code> separator character to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>Append the <a class="tref internalDFN" title="reference_string" href="#dfn-reference_string">reference string</a> to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ </ol>
+ </li><li>Append the <code>]</code> character to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>Append all <a class="tref" title="adjacent_node_labels">adjacent node labels</a> to the
+ <a class="tref" title="label_serialization">label serialization</a> by concatenating the string value
+ for all of them, one after the other, to the
+ <a class="tref" title="label_serialization">label serialization</a>.</li>
+ <li>Push the <a class="tref" title="adjacent_node_labels">adjacent node labels</a> onto the
+ <a class="tref internalDFN" title="key_stack" href="#dfn-key_stack">key stack</a> and append the result of the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>
+ to the <a class="tref" title="label_serialization">label serialization</a>.
+</li></ol>
+
+</div>
+
+</div>
+
+<div class="appendix section" id="acknowledgements">
+
+<!-- OddPage -->
+<h2><span class="secno">A. </span>Acknowledgements</h2>
+
+<p>The editors would like to thank Jeremy Carroll for his work on the
+graph normalization problem. Gavin Carothers for providing valuable feedback
+and testing input for the algorithm defined in this specification. Sir
+Tim Berners Lee for his thoughts on graph normalization over the years.
+Jesús Arias Fisteus for his work on a similar algorithm. Finally, a huge thank
+you goes out to Dave Longley who designed and implemented the algorithms
+used in this specification, which turned out to be a monumentally difficult
+design challenge.
+</p>
+
+</div>
+
+
+
+<div id="references" class="appendix section">
+<!-- OddPage -->
+<h2><span class="secno">B. </span>References</h2><div id="normative-references" class="section"><h3><span class="secno">B.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-RDF-CONCEPTS">[RDF-CONCEPTS]</dt><dd>Graham Klyne; Jeremy J. Carroll. <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210"><cite>Resource Description Framework (RDF): Concepts and Abstract Syntax.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210">http://www.w3.org/TR/2004/REC-rdf-concepts-20040210</a>
+</dd></dl></div><div id="informative-references" class="section"><h3><span class="secno">B.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-RDF-SYNTAX">[RDF-SYNTAX]</dt><dd>Ora Lassila; Ralph R. Swick. <a href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222"><cite>Resource Description Framework (RDF) Model and Syntax Specification.</cite></a> 22 February 1999. W3C Recommendation. URL: <a href="http://www.w3.org/TR/1999/REC-rdf-syntax-19990222">http://www.w3.org/TR/1999/REC-rdf-syntax-19990222</a>
+</dd></dl></div></div></body></html>