Provenance is information about entities, activities, and people involved in producing a piece of data or thing, which can be used to form assessments about its quality, reliability or trustworthiness. Bundles, defined in [[PROV-DM]] as sets of provenance descriptions, were introduced in PROV as the mechanism by which provenance of provenance can be expressed. Bundles, whose validity is established independently of each other [[PROV-CONSTRAINTS]], are essentially independent of each other, acting as islands of provenance descriptions.

In applications where provenance is created by multiple parties over time, it is useful for provenance descriptions created by one party to link to provenance descriptions created by another party. Such a mechanism would allow the "stitching" of provenance descriptions together. Given that provenance descriptions are expected to be contained in bundles, this would require a capability to link entity descriptions across bundles. To address this requirement, this document introduces a relation Mention allowing an entity description to be linked to another entity description occurring in another bundle.

The PROV Document Overview describes the overall state of PROV, and should be read before other PROV documents.

PROV Family of Documents

• PROV-OVERVIEW (Note), an overview of the PROV family of documents [[PROV-OVERVIEW]];
• PROV-PRIMER (Note), a primer for the PROV data model [[PROV-PRIMER]];
• PROV-O (Recommendation), the PROV ontology, an OWL2 ontology allowing the mapping of the PROV data model to RDF [[PROV-O]];
• PROV-DM (Recommendation), the PROV data model for provenance [[PROV-DM]];
• PROV-N (Recommendation), a notation for provenance aimed at human consumption [[PROV-N]];
• PROV-CONSTRAINTS (Recommendation), a set of constraints applying to the PROV data model [[PROV-CONSTRAINTS]];
• PROV-XML (Note), an XML schema for the PROV data model [[PROV-XML]];
• PROV-AQ (Note), mechanisms for accessing and querying provenance [[PROV-AQ]];
• PROV-DICTIONARY (Note) introduces a specific type of collection, consisting of key-entity pairs [[PROV-DICTIONARY]];
• PROV-DC (Note) provides a mapping between PROV-O and Dublin Core Terms [[PROV-DC]];
• PROV-SEM (Note), a declarative specification in terms of first-order logic of the PROV data model [[PROV-SEM]];
• PROV-LINKS (Note) introduces a mechanism to link across bundles (this document).

Implementations Encouraged

The Provenance Working Group encourages implementation of the material defined in this document. Although work on this document by the Provenance Working Group is complete, errors may be recorded in the errata or and these may be addressed in future revisions.

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Introduction

The PROV data model [[PROV-DM]] defines provenance as a record that describes the people, institutions, entities, and activities involved in producing, influencing, or delivering a piece of data or a thing. The specifications [[PROV-O]], [[PROV-DM]], [[PROV-N]], and [[PROV-XML]] have respectively defined the PROV ontology, the PROV conceptual model, the PROV notation, and the PROV XML schema, allowing provenance descriptions to be expressed, represented in various ways, and interchanged between systems across the Web.

The provenance of information is crucial in deciding whether information is to be trusted, how it should be integrated with other diverse information sources, and how to give credit to its originators when reusing it. To support this, provenance itself should be trusted, and therefore, provenance of provenance is itself an important aspect of establishing trust in an information infrastructure such as the Web. To this end, PROV introduces the concept of Bundle: defined as a named set of provenance descriptions; it is a mechanism by which provenance of provenance can be expressed (see also Bundle [[PROV-O]], Bundle [[PROV-N]] and Bundle [[PROV-XML]]). With bundles, sets of provenance descriptions can be given names and can themselves be regarded as entities, whose provenance can in turn be described using PROV. These sets of provenance descriptions stand independently of each other, as formalized by [[PROV-CONSTRAINTS]] which determines their validity by examining them in isolation of each other.

In a distributed environment, it is common to encounter applications that involve multiple parties: it is a common situation that some party (a producer) creates some data and its provenance, whereas another party (a consumer) consumes the data and its provenance. In such a situation, the consumer, when it in turn generates provenance, often wants to augment the descriptions of entities generated by the producer. For the consumer, it is not suitable to repeat the provenance created by the producer, and augment it according to their need. Instead, a consumer wants to refer to the description as created by the producer in situ and specialize it, allowing the consumer to add their own view on this entity. (The notion of specialization is defined in [[PROV-DM]].) Such a capability would allow parties to "stitch together" provenance descriptions that would otherwise be disconnected. For this to work, this specification assume that provenance created by the producer is contained in a bundle, so that others such as the consumer, can refer to it, by means of the bundle identifier.

While URIs are the Web mechanism by which entities can be assigned identities, URIs alone are not sufficient for our purpose. Indeed, the entity produced by the producer is given a URI, but the same entity, with the same URI, could also be described in other bundles, by this producer or third parties. It is the capability of referring to the description of the entity, as created by the producer in a specific bundle, that is of interest to us in this specification.

This specification introduces a new concept Mention allowing an entity to be described as the specialization of another entity, itself described in another bundle. This specification provides not only a conceptual definition of Mention, but also the corresponding ontological, schema, and notational definitions, for the various representations of PROV. It also includes constraints that apply to this construct specifically. It is our aim to promote interoperability by defining Mention conceptually and in the representations of PROV.

Conceptual Definition of Mention

An entity e1 may be mentioned in a bundle b, which contains some descriptions about this entity e1: how e1 was generated and used, which activities e1 is involved with, the agents e1 is attributed to, etc. Other bundles may contain other descriptions about the same entity e1.

Some applications may want to augment the descriptions of entity e1 found in a bundle b with other information. They cannot add these descriptions to bundle b since this would result in a different bundle. Alternatively, they may create a new bundle with descriptions from bundle b and novel descriptions, but this results in an undesirable copy of the bundle.

To this end, PROV allows a new entity e2 to be created and defined as a specialization of the preceding entity e1, and which presents at least an additional aspect: the bundle b containing some descriptions of e1. With this relation, applications that process e2 can know that the attributes of e2 may have been computed according to the descriptions of e1 in b. (The term 'aspect' should be understood informally as "a particular part or feature of something"; the term is used in [[PROV-DM]]'s definitions of entity (Section 5.1.1), specialization (Section 5.5.1), alternate (Section 5.5.2), and in section 2.1 of [[PROV-CONSTRAINTS]]).

Figure 1 depicts the relation MentionOf (concept Mention) as a ternary relation.

Thus, a mention relates two entities with regard to a bundle. It is a special case of specialization.

An entity is interpreted with respect to a bundle's description in a domain specific manner. The mention of this entity with respect to this bundle offers the opportunity to specialize it according to some domain-specific interpretation.

A mention of an entity in a bundle results in a specialization of this entity with extra fixed aspects, including the bundle that it is described in.

Like specialization, a mention is not, as defined here, an influence, and therefore does not have an id and attributes. Its grammar, in the provenance notation, is written as follows.

The following table summarizes how each constituent of a Mention maps to a syntax element, in the provenance notation.

We note that prov:mentionOf cannot be inferred from Specialization. Indeed, let us consider a bundle and the expression specializationOf(e2,e1) occuring in this bundle. The entity e1 may be described in multiple other bundles b_i. From specializationOf(e2,e1), one cannot infer prov:mentionOf(e2,e1,b) for a given b, since it is unknown which b_i's descriptions were used to compute additional aspects of e2. Hence, prov:mentionOf has to be asserted.

We note that the concept Mention is an extension of the PROV data model [[PROV-DM]]; therefore, its textual notation has to be prefixed, prov:mentionOf, according the extensibility rules of the provenance notation [[PROV-N]].

TBD presents constraints applicable to Mention, and in particular, the fact that an entity can be a specific entity of a Mention at most once.

bundle ex:run1
    activity(ex:a1, 2011-11-16T16:00:00, 2011-11-16T17:00:00)  //duration: 1hour
    wasAssociatedWith(ex:a1, ex:Bob, [prov:role='ex:controller'])
endBundle

bundle ex:run2
    activity(ex:a2, 2011-11-17T10:00:00, 2011-11-17T17:00:00)  //duration: 7hours
    wasAssociatedWith(ex:a2, ex:Bob, [prov:role='ex:controller'])
endBundle

bundle tool:analysis01
    agent(tool:Bob-2011-11-16, [perf:rating="good"])
    prov:mentionOf(tool:Bob-2011-11-16, ex:Bob, ex:run1)

    agent(tool:Bob-2011-11-17, [perf:rating="bad"])
    prov:mentionOf(tool:Bob-2011-11-17, ex:Bob, ex:run2)
endBundle

 
bundle obs:bundle1
  entity(ex:report1, [ prov:type="report", ex:version=1 ])
  wasGeneratedBy(ex:report1, -, 2012-05-24T10:00:01)
  entity(ex:report2, [ prov:type="report", ex:version=2 ])
  wasGeneratedBy(ex:report2, -, 2012-05-25T11:00:01)
  wasDerivedFrom(ex:report2, ex:report1)
endBundle

 
entity(obs:bundle1, [ prov:type='prov:Bundle' ])
wasAttributedTo(obs:bundle1, ex:observer01)

 
bundle tool:bundle2
  entity(tool:bundle2, [ prov:type='viz:Configuration', prov:type='prov:Bundle' ])
  wasAttributedTo(tool:bundle2, viz:Visualizer)

  entity(tool:report1, [ viz:color="orange" ])
  prov:mentionOf(tool:report1, ex:report1, obs:bundle1)

  entity(tool:report2, [ viz:color="blue" ])              
  prov:mentionOf(tool:report2, ex:report2, obs:bundle1)
endBundle

Ontological Definition of Mention

The properties defined in this document are included in the default namespace of PROV. Users of the ontology have the option of importing <http://www.w3.org/ns/prov#>, which includes all extensions, including PROV-Links. Additionally, the [OWL file for PROV-Links] is available for download.

The ternary relation Mention is encoded as two properties: prov:mentionOf and prov:asInBundle, defined as follows.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xsd:  <http://www.w3.org/2001/XMLSchema#> .
@prefix owl:  <http://www.w3.org/2002/07/owl#> .
@prefix prov: <http://www.w3.org/ns/prov#> .
@prefix tool: <http://example.com/tool/> .
@prefix perf: <http://example.com/performance/> .
@prefix :     <http://example.com/> .

:run2 {
   :activity_2
      a prov:Activity;
      prov:startedAtTime "2011-11-17T10:00:00"^^xsd:dateTime;
      prov:endedAtTime   "2011-11-17T17:00:00"^^xsd:dateTime; 
      prov:wasAssociatedWith :bob;
   .
}

tool:analysis01 {
   tool:bob-2011-11-17
      a prov:Agent;
      prov:mentionOf  :bob;
      prov:asInBundle :run2;
      perf:rating     perf:very-slow;
   .

    # This is inferred from prov:mentionOf
    tool:bob-2011-11-17 prov:specializationOf :bob . 
}

XML Schema for Mention

The [XML schema for PROV-Links] is available for download, and includes prov-core.xsd, the core schema of PROV. Alternatively, the default schema, prov.xsd can be used, which imports prov-core.xsd all extension schemas developed by the Working Group.

Type definition in XML Schema:

<xs:complexType xmlns:xs="http://www.w3.org/2001/XMLSchema" name="Mention">
  <xs:sequence>
    <xs:element name="specificEntity" type="prov:IDRef"/>
    <xs:element name="generalEntity" type="prov:IDRef"/>
    <xs:element name="bundle" type="prov:IDRef"/>
  </xs:sequence>
</xs:complexType>

Usage in XML:

<xs:element xmlns:xs="http://www.w3.org/2001/XMLSchema" name="mentionOf" type="prov:Mention" substitutionGroup="prov:internalElement"/>

<prov:document
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:prov="http://www.w3.org/ns/prov#"
    xmlns:ex="http://example.com/ns/ex#"
    xmlns:perf="http://example.com/ns/perf#"
    xmlns:tool="http://example.com/ns/tool#">

  <prov:bundleContent prov:id="ex:run1">
    <prov:activity prov:id="ex:a1">
      <prov:startTime>2011-11-16T16:00:00</prov:startTime>
      <prov:endTime>2011-11-16T17:00:00</prov:endTime>
    </prov:activity>

    <prov:wasAssociatedWith>
      <prov:activity prov:ref="ex:a1" />
      <prov:agent prov:ref="ex:Bob" />
      <prov:role xsi:type="xsd:QName">ex:controller</prov:role>
    </prov:wasAssociatedWith>
  </prov:bundleContent>

  <prov:bundleContent prov:id="ex:run2">
    <prov:activity prov:id="ex:a2">
      <prov:startTime>2011-11-17T10:00:00</prov:startTime>
      <prov:endTime>2011-11-17T17:00:00</prov:endTime>
    </prov:activity>

    <prov:wasAssociatedWith>
      <prov:activity prov:ref="ex:a2" />
      <prov:agent prov:ref="ex:Bob" />
      <prov:role xsi:type="xsd:QName">ex:controller</prov:role>
    </prov:wasAssociatedWith>
  </prov:bundleContent>

  <prov:bundleContent prov:id="tool:analysis01">
    <prov:agent prov:id="tool:Bob-2011-11-16">
      <perf:rating>good</perf:rating>
    </prov:agent>

    <prov:mentionOf>
      <prov:specificEntity prov:ref="tool:Bob-2011-11-16" />
      <prov:generalEntity prov:ref="ex:Bob" />
      <prov:bundle prov:ref="ex:run1" />
    </prov:mentionOf>

    <prov:agent prov:id="tool:Bob-2011-11-17">
      <perf:rating>bad</perf:rating>
    </prov:agent>

    <prov:mentionOf>
      <prov:specificEntity prov:ref="tool:Bob-2011-11-17" />
      <prov:generalEntity prov:ref="ex:Bob" />
      <prov:bundle prov:ref="ex:run2" />
    </prov:mentionOf>
  </prov:bundleContent>

</prov:document>

Constraints associated with Mention

If one entity is a mention of another in a bundle, then the former is also a specialization of the latter: