--- a/model/working-copy/wd5-prov-dm-constraints-revised.html Fri Apr 13 21:10:57 2012 -0400
+++ b/model/working-copy/wd5-prov-dm-constraints-revised.html Sat Apr 14 14:55:42 2012 +0100
@@ -201,13 +201,13 @@
<h4>Fourth Public Working Draft</h4>
-<p>This is the fourth public release of the PROV-DM
+ <p>This is the fourth public release of the PROV-DM
document. Following feedback, the Working Group has decided to
reorganize this document substantially, separating the data model,
from its contraints, and the notation used to illustrate it. The
PROV-DM release is synchronized with the release of the PROV-O,
-PROV-PRIMER, PROV-N, PROV-DM-CONSTRAINTS documents. @@TODO: Describe
-the order of reading the documents.</p>
+PROV-PRIMER, PROV-N, PROV-DM-CONSTRAINTS documents.
+</p>
</section>
@@ -327,10 +327,12 @@
<section id='prov-dm-refinement'>
<h2>Data Model Refinement</h2>
-<div class='note>TODO: Better section title/headings; move this
+<div class='note'>TODO: Better section title/headings; move this
material later or embed it into appropriate sections</div>
-<p>The PROV-DM data model is implicitly based on a notion of event, marking
+<p>The PROV-DM data model is implicitly based on a notion of <dfn
+ id="dfn-event">instantaneous event</dfn>s (or just <a
+ title="instantaneous event">event</a>s), that mark
transitions in the world. Events include generation, usage, or
invalidation of entities, as well as starting or ending of activities. This
notion of event is not first-class in the data model, but it is useful
@@ -364,8 +366,7 @@
-->
<p>Hence, to talk about the constraints on valid PROV-DM data, we
-refer to <em>instantaneous events</em>, or <dfn
-id="dfn-event">events</dfn> for short, that correspond to interactions
+refer to <a title="instantaneous event">instantaneous events</a> that correspond to interactions
between activities and entities.
The term "event" is commonly used in process algebra with a similar meaning. For instance, in CSP [[CSP]], events represent communications or interactions; they are assumed to be atomic and
instantaneous.</p>
@@ -378,13 +379,13 @@
<h4>Event Ordering</h4>
<p>To allow for minimalistic clock assumptions, like Lamport
-[[CLOCK]], PROV-DM relies on a notion of relative ordering of <a title="event">instantaneous events</a>,
-without using physical clocks. This specification assumes that a partial order exists between <a title="event">instantaneous events</a>.
+[[CLOCK]], PROV-DM relies on a notion of relative ordering of <a title="instantaneous event">instantaneous events</a>,
+without using physical clocks. This specification assumes that a partial order exists between <a title="instantaneous event">instantaneous events</a>.
</p>
<p>Specifically, <dfn id="dfn-precedes">precedes</dfn> is a partial
-order between <a title="event">instantaneous events</a>. When we say
+order between <a title="instantaneous event">instantaneous events</a>. When we say
<span class="name">e1</span> precedes <span class="name">e2</span>,
this means that either the two events are equal or <span
class="name">e1</span> happened before <span class="name">e2</span>.
@@ -412,7 +413,7 @@
</div>
<p> How such a partial order is implemented in practice is beyond the scope
of this specification. This specification only assumes that
-each <a title="event">instantaneous event</a> can be mapped to an instant in some form of
+each <a title="instantaneous event">instantaneous event</a> can be mapped to an instant in some form of
timeline. The actual mapping is not in scope of this
specification. Likewise, whether this timeline is formed of a single
global timeline or whether it consists of multiple Lamport-style
@@ -424,15 +425,15 @@
<p>This specification defines <i>event ordering constraints</i>
-between <a title="event">instantaneous events</a> associated with
+between <a title="instantaneous event">instantaneous events</a> associated with
provenance descriptions. PROV-DM data MUST satisfy such constraints. </p>
<p>PROV-DM also allows for time observations to be inserted in
specific descriptions, for each recognized <a
- title="event">instantaneous event</a> introduced in this
+ title="instantaneous event">instantaneous event</a> introduced in this
specification. The presence of a time observation for a given <a
- title="event">instantaneous event</a> fixes the mapping of this <a
- title="event">instantaneous event</a> to the timeline. It can also
+ title="instantaneous event">instantaneous event</a> fixes the mapping of this <a
+ title="instantaneous event">instantaneous event</a> to the timeline. It can also
help with the verification of associated ordering constraints (though,
again, this verification is outside the scope of this specification).
</p>
@@ -444,32 +445,34 @@
<section id="types-of-events">
<h4>Types of Events</h4>
-<p>Five kinds of <a title="event">instantaneous events</a> are used
-for the PROV-DM data model. The <strong>activity start</strong> and <strong>activity end</strong> events demarcate the
-beginning and the end of activities, respectively. The <strong>entity
-usage</strong>, <strong>entity generation</strong>, and <strong>entity invalidation</strong> events demarcate the characterization interval for entities. More
-specifically:
+<p>Five kinds of <a title="instantaneous event">instantaneous events</a> are used
+for the PROV-DM data model. The <strong>activity start</strong> and
+<strong>activity end</strong> events delimit the beginning and the end
+of activities, respectively. The <strong>entity usage</strong>,
+<strong>entity generation</strong>, and <strong>entity
+invalidation</strong> events apply to entities, and the generation and
+invalidation events delimit the <a title="characterization interval">characterization interval</a> of
+an entity. More specifically:
</p>
-<p>An <dfn id="dfn-start-event">activity start event</dfn> is the <a title="event">instantaneous event</a> that marks the instant an activity starts.</p>
-
-<p>An <dfn id="dfn-end-event">activity end event</dfn> is the <a title="event">instantaneous event</a> that marks the instant an activity ends.</p>
+<p>An <dfn id="dfn-start-event">activity start event</dfn> is the <a title="instantaneous event">instantaneous event</a> that marks the instant an activity starts.</p>
+
+<p>An <dfn id="dfn-end-event">activity end event</dfn> is the <a title="instantaneous event">instantaneous event</a> that marks the instant an activity ends.</p>
<p>An <dfn id="dfn-usage-event">entity usage event</dfn> is the <a
-title="event">instantaneous event</a> that marks the first instant of
+title="instantaneous event">instantaneous event</a> that marks the first instant of
an entity's consumption timespan by an activity.</p>
-<p>An <dfn id="dfn-generation-event">entity generation event</dfn> is the <a title="event">instantaneous event</a> that marks the final instant of an entity's creation timespan, after which
+<p>An <dfn id="dfn-generation-event">entity generation event</dfn> is the <a title="instantaneous event">instantaneous event</a> that marks the final instant of an entity's creation timespan, after which
it is available for use.</p>
-<p>An <dfn id="dfn-invalidation-event">entity invalidation event</dfn> is the <a title="event">instantaneous event</a> that marks the initial instant of the destruction, invalidation, or cessation of an entity, after which the entity is no longer available for use.</p>
+<p>An <dfn id="dfn-invalidation-event">entity invalidation event</dfn> is the <a title="instantaneous event">instantaneous event</a> that marks the initial instant of the destruction, invalidation, or cessation of an entity, after which the entity is no longer available for use.</p>
</section>
- </section>
-
-
+
+</section>
<section id='section-attributes'>
<h4>Entities and Attributes</h4>
@@ -508,16 +511,19 @@
<p>
An <dfn>entity</dfn> is a thing one wants to provide provenance for
and whose situation in the world is described by some fixed
-attributes. An entity has a characterization interval, or lifetime,
-defined as characterization interval, which is defined as the period
+attributes. An entity has a <dfn
+id="|dfn-characterization-interval">characterization interval</dfn>,
+or <dfn id="lifetime">lifetime</dfn>,
+defined as the period
between its <a title="entity generation event">generation event</a>
and its <a title="entity invalidation event">invalidation event</a>.
An entity's attributes are established when the entity is
created and describe the entity's situation and (partial) state
during an entity's lifetime.</p>
-<p>An entity fixes some aspects of a thing and its situation in the
-world. A different entity (perhaps representing a different user or
+<p><!--An entity fixes some aspects of a thing and its situation in the
+world.-->
+A different entity (perhaps representing a different user or
system perspective) may fix other aspects of the same thing, and its provenance
may be different. Different entities that are aspects of the same
thing are called <em>alternate</em>, and the PROV-DM relations of
@@ -530,7 +536,8 @@
<div class="anexample" id="a-report-example">
Different users may take different perspectives on a resource with
-a URL. For each perspective, an entity may be expressed as:
+a URL. A provenance record might use one (or more) different
+ entities to talk about different persectives, such as:
<ul>
<li>a report available at a URL: fixes the nature of the thing, i.e. a document, and its location; </li>
<li>the version of the report available there today: fixes its version number, contents, and its date;</li>
@@ -542,13 +549,13 @@
<li>the provenance of the report independent of where it is hosted over time may include: the motivation for writing the report, the overall methodology for producing it, and the broad team
involved in it.</li>
</ul>
-</div>
-
<p>We do not assume that any entity is a better or worse description of
reality than any other. That is, we do not assume an absolute ground truth with
respect to which we can judge correctness or completeness of
descriptions. In fact, it is possible to describe the processing that occurred for the report to be commissioned, for
individual versions to be created, for those versions to be published at the given URL, etc., each via a different entity with attribute-value pairs that fix some aspects of the report appropriately.</p>
+</div>
+
<p>Besides entities, a variety of other PROV-DM objects have
attributes, including activity, generation, usage, start, end,
@@ -562,8 +569,11 @@
are considered to be fixed aspects
of underlying, changing things. This means, for example, that
if two entities have overlapping lifetimes and they have some
-attributes in common, those attributes SHOULD match. @@TODO:
-Constraints for this?</p>
+attributes in common, those attributes SHOULD match. </p>
+<div class="note">
+ @@TODO:
+Constraints for this?
+ </div>
</section>
@@ -626,13 +636,16 @@
they were generated, etc. In other words, an important requirement is
to be able to express the provenance of provenance. </p>
+<div class="note">
+ See ISSUE-343. Also, what is an account's set of descriptions?
+ </div>
<p>
<span class="glossary" id="glossary-account">
-An <dfn>account</dfn> is a entity that contains a bundle of provenance descriptions.
+An <dfn>account</dfn> is an entity that contains a bundle of provenance descriptions.
</span> PROV-DM does not provide an actual mechanism for creating accounts, i.e. for bundling up provenance descriptions and naming them. Accounts MUST satisfy some properties:
<ul>
-<li>An account is as a container of provenance descriptions, hence its content MAY change over time.</li>
-<li>If an account's set of descriptions changes over time, it increases monotonically with time. </li>
+<li>An account is a bundle of provenance descriptions whose content MAY change over time.</li>
+<li>If an account's set of descriptions changes over time, it SHOULD increase monotonically with time. </li>
<li>A given description of e.g. an entity in a given account, in terms of its identifier and attribute-value pairs, does not change over time. </li>
</ul>
@@ -674,8 +687,13 @@
<p>
-An <dfn>entity</dfn> is a thing one wants to provide provenance for and whose situation in the world is described by some attribute-value pairs. An entity's attribute-value pairs are specified when the entity description is created and remain unchanged. An entity's attribute-value pairs are expected to describe the entity's situation and (partial) state during an entity's characterization interval,
- i.e. a continuous interval between two <a title="event">instantaneous events</a>, namely its <a title="entity generation event">generation event</a> and its <a title="entity invalidation event">invalidation event</a>.</p>
+An <dfn>entity</dfn> is a thing one wants to provide provenance for
+and whose situation in the world is described by some attribute-value
+pairs. An entity's attribute-value pairs are established as part of
+the entity description and their values remain unchanged for the
+lifetime of the entity. An entity's attribute-value pairs are expected
+to describe the entity's situation and (partial) state during an
+entity's <a title="characterization interval">characterization interval</a>.</p>
<p>If an entity's situation or state changes, this may result in its description being invalid, because one or more attribute-value pairs no longer hold. In that case, from the PROV viewpoint, there exists a new entity, which needs to be given a distinct identifier, and associated with the attribute-value pairs that reflect its new situation or state.</p>
@@ -683,7 +701,16 @@
Further considerations:
<ul>
-<li>In order to describe something over several intervals, it is required to create multiple entities, each with its own identifier. This allow potential dependencies between the various entities to be expressed.
+<li>In order to describe the provenance of something during an interval over which
+ relevant attributes of the thing are not fixed, it is required to
+ create multiple entities, each with its own identifier, <a
+ title="characterization interval">characterization interval</a>, and
+ fixed attributes, and express
+ dependencies between the various entities using events.
+ For example, if we want to describe the provenance of several
+ versions of a document, involving attributes such as authorship that
+ change over time, we need different entities for the versions linked
+ by appropriate generation, usage, revision, and invalidation events.
</li>
<li>There is no assumption that the set of attributes is complete, nor
@@ -691,7 +718,7 @@
<li>There is no assumption that the attributes of an entity uniquely
identify it. Two different entities that are aspects of different
things can have the same attributes.</li>
-<li>A characterization interval may collapse into a single instant.</li>
+<li>A <a title="characterization interval">characterization interval</a> may collapse into a single instant.</li>
</ul>
@@ -710,7 +737,7 @@
<p>An activity is delimited by its <a title="activity start event">start</a> and its <a title="activity end event">end</a> events; hence, it occurs over
-an interval delimited by two <a title="event">instantaneous
+an interval delimited by two <a title="instantaneous event">instantaneous
events</a>. However, an activity record need not mention start or end time information, because they may not be known.
An activity's attribute-value pairs are expected to describe the activity's situation during its interval, i.e. an interval between two instantaneous events, namely its <a title="activity start event">start</a> event and its <a title="activity end event">end</a> event.
</p>
@@ -738,10 +765,17 @@
<section id="term-Generation">
<h4>Generation</h4>
-
-
-<p>A <dfn id="dfn-Generation">generation</dfn> is an instantaneous world <a title="entity generation event">event</a>, the completed creation of a new
-entity by an activity. This entity becomes available for usage after this <a title="event">instantaneous
+<div class="note">
+ ISSUE-346 (BLOCKING): Distinction between constraints,
+ interpretations, inferences not clear and hard to follow in text
+ here.
+
+ Navigation links among constraints, inferences, and definitions are
+ broken or confusing. Section to be reorganized.
+ </div>
+
+<p>A <dfn id="dfn-Generation">generation</dfn> is an <a title="instantaneous event">instantaneous event</a>, the completed creation of a new
+entity by an activity. This entity becomes available for usage after this <a title="instantaneous event">instantaneous
event</a>. This entity did not exist before creation.
Generation events can have attributes that describe how the entity was
generated by the activity..</p>
@@ -750,7 +784,7 @@
<p>
-A generation's id is OPTIONAL. It MUST be used when annotating generations or when defining
+A generation's identifier is OPTIONAL. It MUST be used when annotating generations or when defining
derivations (see <a href="#Derivation-Relation">Derivation</a>).
</p>
@@ -784,7 +818,7 @@
-<p>A <dfn id="dfn-Use">usage</dfn> is an instantaneous world <a title="entity usage event">event</a>: an activity beginning to consume an entity.
+<p>A <dfn id="dfn-Use">usage</dfn> is an <a title="instantaneous event">instantaneous event</a>: an activity beginning to consume an entity.
Before this event, the activity had not begun to consume or use to this entity.
The description includes the modalities of usage of this entity by this activity.</p>
@@ -792,7 +826,7 @@
<p>
-A usage id is OPTIONAL. It MUST be present when annotating usages or when defining derivations (see
+A usage identifier is OPTIONAL. It MUST be present when annotating usages or when defining derivations (see
<a href="#Derivation-Relation">Derivation</a>).</p>
<p>
@@ -812,7 +846,7 @@
<h3>Start</h3>
-<p>An <a>activity start event</a> is the <a title="event">instantaneous event</a> that marks the instant an activity starts. It allows for an optional time attribute. <span id="optional-attributes2">Activities also allow for an optional start time attribute. If both are specified, they MUST be the same, as expressed by the following constraint.</span>
+<p>An <a>activity start event</a> is the <a title="instantaneous event">instantaneous event</a> that marks the instant an activity starts. It allows for an optional time attribute. <span id="optional-attributes2">Activities also allow for an optional start time attribute. If both are specified, they MUST be the same, as expressed by the following constraint.</span>
</p>
<div class='constraint' id='unique-startTime'>
@@ -824,7 +858,7 @@
<h3>End</h3>
-<p>An <a>activity end event</a> is the <a title="event">instantaneous event</a> that marks the instant an activity ends. It allows for an optional time attribute. <span id="optional-attributes3">Activities also allow for an optional end time attribute. If both are specified, they MUST be the same, as expressed by the following constraint.</span>
+<p>An <a>activity end event</a> is the <a title="instantaneous event">instantaneous event</a> that marks the instant an activity ends. It allows for an optional time attribute. <span id="optional-attributes3">Activities also allow for an optional end time attribute. If both are specified, they MUST be the same, as expressed by the following constraint.</span>
</p>
<div class='constraint' id='unique-endTime'>
@@ -988,9 +1022,12 @@
<span class="name">a2</span> acts on behalf of <span
class="name">a1</span> for all activities with which <span
class="name">a2</span> is
- associated. @@TODO: Could this be an inference? Does it imply that
- a1 is associated with all activities a2 is associated with?</p>
+ associated.
</div>
+<div class="note">
+ @@TODO: Could this be an inference? Does it imply that
+ a1 is associated with all activities a2 is associated with?
+ </div></p>
<div class="interpretation-forward">
For the interpretation of responsibility, see <a href="#actedOnBehalfOf-ordering">actedOnBehalfOf-ordering</a>.
@@ -1352,14 +1389,14 @@
<h3>PROV-DM Event Ordering Constraints</h3>
<p>Section <a href="#section-time-event">section-time-event</a>
-introduces a notion of <a title="event">instantaneous event</a>
+introduces a notion of <a title="instantaneous event">instantaneous event</a>
marking changes in the world, in its activities and entities. PROV-DM
-identifies five kinds of <a title="event">instantaneous events</a>, namely <a>entity generation
+identifies five kinds of <a title="instantaneous event">instantaneous events</a>, namely <a>entity generation
event</a>, <a>entity usage event</a>, <a>entity invalidation event</a>, <a>activity start event</a>
and <a>activity end event</a>. PROV-DM adopts Lamport's clock
assumptions [[CLOCK]] in the form of a reflexive, transitive partial order <a>follows</a>
-(and its inverse <a>precedes</a>) between <a title="event">instantaneous events</a>. Furthermore,
-PROV-DM assumes the existence of a mapping from <a title="event">instantaneous events</a> to time clocks,
+(and its inverse <a>precedes</a>) between <a title="instantaneous event">instantaneous events</a>. Furthermore,
+PROV-DM assumes the existence of a mapping from <a title="instantaneous event">instantaneous events</a> to time clocks,
though the actual mapping is not in scope of this specification.</p>
<p>Given that provenance consists of a description of past entities
@@ -1377,7 +1414,7 @@
<p>PROV-DM also allows for time observations to be inserted in
specific provenance descriptions, for each of the five kinds
-of <a title="event">instantaneous events</a> introduced in this specification. The
+of <a title="instantaneous event">instantaneous events</a> introduced in this specification. The
presence of a time observation for a given <a>instantaneous event</a> fixes the
mapping of this <a>instantaneous event</a> to the timeline. The presence of time
information in a provenance description instantiates the ordering constraint with
@@ -1392,16 +1429,16 @@
right. Activities are represented by rectangles, whereas entities are
represented by circles. Usage, generation and derivation are
represented by the corresponding edges between entities and
-activities. The five kinds of <a title="event">instantaneous events</a> are represented by vertical
+activities. The five kinds of <a title="instantaneous event">instantaneous events</a> are represented by vertical
dotted lines (adjacent to the vertical sides of an activity's
rectangle, or intersecting usage and generation edges). The ordering
-constraints are represented by triangles: an occurrence of a triangle between two <a title="event">instantaneous event</a> vertical dotted lines represents that the event denoted by the left
+constraints are represented by triangles: an occurrence of a triangle between two <a title="instantaneous event">instantaneous event</a> vertical dotted lines represents that the event denoted by the left
line precedes the event denoted by the right line.</p>
<div style="text-align: center;">
<figure>
+<figcaption id="constraint-summary">Summary of <a title="instantaneous event">instantaneous event</a> ordering constraints</figcaption>
<img src="images/constraints.png" alt="constraints between events" />
-<figcaption id="constraint-summary">Summary of <a title="event">instantaneous event</a> ordering constraints</figcaption>
</figure>
</div>
@@ -1414,7 +1451,7 @@
<div class='interpretation' id='start-precedes-end'> The following ordering constraint holds for any activity: the
<a title="activity start event">start event</a> <a>precedes</a> the <a title="activity end event">end event</a>.</div>
-<p> A usage and a generation for a given entity implies ordering of <a title="event">events</a>, since the <a title="entity generation
+<p> A usage and a generation for a given entity implies ordering of <a title="instantaneous event">events</a>, since the <a title="entity generation
event">generation event</a> had to precede the <a title="entity usage event">usage event</a>. This is
illustrated by Subfigure <a href="#constraint-summary">constraint-summary</a> (b) and expressed by constraint <a href="#generation-precedes-usage">generation-precedes-usage</a>.</p>
@@ -1422,6 +1459,9 @@
<a>precedes</a> any of its <a title="entity usage event">usages</a>.
</div>
+<div class="note">
+ISSUE-345: does not clearly delineate where the discussion for one constraint starts and where the next ends.
+ </div>
<p>Invalidation is defined at the event at which an entity ceases to exist as such. All usages of an entity precede its invalidation, which is captured by constraint <a href="#usage-precedes-invalidation">usage-precedes-invalidation</a> (without any explicit graphical representation).</p>
@@ -1440,7 +1480,7 @@
<a>precedes</a> its <a title="entity invalidation event">invalidation</a>.
</div>
-<p>A usage implies ordering of <a title="event">events</a>, since the <a title="entity usage event">usage event</a> had to occur during the associated activity. This is
+<p>A usage implies ordering of <a title="instantaneous event">events</a>, since the <a title="entity usage event">usage event</a> had to occur during the associated activity. This is
illustrated by Subfigure <a href="#constraint-summary">constraint-summary</a> (c) and expressed by constraint <a href="#usage-within-activity">usage-within-activity</a>.</p>
<div class='interpretation' id='usage-within-activity'>Given an activity with identifier <span class="name">a</span>, an entity with identifier <span class="name">e</span>, a set
@@ -1452,7 +1492,7 @@
-<p>A generation implies ordering of <a title="event">events</a>, since the <a title="entity generation event">generation event</a> had to occur during the associated activity. This is
+<p>A generation implies ordering of <a title="instantaneous event">events</a>, since the <a title="entity generation event">generation event</a> had to occur during the associated activity. This is
illustrated by Subfigure <a href="#constraint-summary">constraint-summary</a> (d) and expressed by constraint <a href="#generation-within-activity">generation-within-activity</a>.</p>
<div class='interpretation' id='generation-within-activity'>Given an activity with identifier <span class="name">a</span>, an entity with identifier <span class="name">e</span>, a set
@@ -1504,7 +1544,7 @@
generation of <span class="name">e2</span>. </p>
<p>Communication between two activities <span class="name">a1</span> and <span class="name">a2</span> also implies ordering of <a
-title="event">events</a>, since some entity must have been generated by the former and used by the latter, which implies that the start event of <span class="name">a1</span>
+title="instantaneous event">events</a>, since some entity must have been generated by the former and used by the latter, which implies that the start event of <span class="name">a1</span>
cannot follow the end event of <span class="name">a2</span>. This is
illustrated by Subfigure <a href="#constraint-summary">constraint-summary</a> (g) and expressed by constraint <a href="#wasInformedBy-ordering">wasInformedBy-ordering</a>.</p>
@@ -1517,7 +1557,7 @@
</div>
<p>Start of <span class="name">a2</span> by activity <span class="name">a1</span> also implies ordering of <a
-title="event">events</a>, since <span class="name">a1</span> must have been active before <span class="name">a2</span> started. This is
+title="instantaneous event">events</a>, since <span class="name">a1</span> must have been active before <span class="name">a2</span> started. This is
illustrated by Subfigure <a href="#constraint-summary">constraint-summary</a> (h) and expressed by constraint <a href="#wasStartedBy-ordering">wasStartedBy-ordering</a>.</p>
@@ -1534,8 +1574,8 @@
<div style="text-align: center;">
<figure>
+<figcaption id="constraint-summary2">Summary of <a title="instantaneous event">instantaneous event</a> ordering constraints (continued)</figcaption>
<img src="../images/constraints2.png" alt="further constraints between events" />
-<figcaption id="constraint-summary2">Summary of <a title="event">instantaneous event</a> ordering constraints (continued)</figcaption>
</figure>
</div>
@@ -2146,7 +2186,7 @@
</pre>
<div class='note'>
Speculative, since we have not defined the invalidation event (yet?.
-What is the meaning here? that only the versions that existed during this characterization interval were attributed to ex:Simon.
+What is the meaning here? that only the versions that existed during this <a title="characterization interval">characterization interval</a> were attributed to ex:Simon.
</div>
</li>