=Paper=
{{Paper
|id=Vol-201/paper-35
|storemode=property
|title=Towards an OWL Ontology for Identity on the Web
|pdfUrl=https://ceur-ws.org/Vol-201/43.pdf
|volume=Vol-201
|dblpUrl=https://dblp.org/rec/conf/swap/GangemiP06
}}
==Towards an OWL Ontology for Identity on the Web==
https://ceur-ws.org/Vol-201/43.pdf
Towards an OWL ontology for identity on the web
Valentina Presutti Aldo Gangemi
Laboratory for Applied Ontology Laboratory for Applied Ontology
National Research Council (ISTC-CNR) National Research Council (ISTC-CNR)
Roma, Italy Roma, Italy
Email: valentina.presutti@istc.cnr.it Email: aldo.gangemi@istc.cnr.it
Abstract— One of the main strength of the web is that it realizes confusion has led to lack of consensus on which is the most
the goal of allowing any party of its global community to share suitable way to solve the problem of handling the recognition
information with any other party. This has been achieved by of the identity of an element that is referenced by a URI,
making use of a unique and uniform mechanism of identification,
the URI (Universal Resource Identifiers). Web applications such and consequently there is not a defined operational semantics
as search engines have been built up on this mechanism. Although associated with each of these different sorts.
URIs succeed when used for retrieving resources on the web, We propose an OWL [30] ontology named IRE (Identifiers,
their suitability as a way for identifying any kind of things, for Resources, and Entities) that was originally formalized in first
example resources that are not on the web, is not guaranteed. order logic, containing concepts that compose the architecture
We investigate the meaning of identity of a web resource and
how it can be modeled in order to be implemented on the web. of the web. IRE is based on an ontology of Information Objects
In particular, we propose an ontology that models the problem, [2], built on top of DOLCE and on some of its modular
and discuss some possible solutions. We describe the concept of extensions [23], [13]. For a complete report the reader can
resource from the web domain point of view, using an ontology refer to [12], [22], [25], [2], while all OWL files are available
of Information Objects, built on top of DOLCE and of some of at http://www.loa-cnr.it/ontologies. IRE provides the basis for
its modular extensions. In particular, we formalize some concepts
of a web resource, and distinguish them from the concept of a defining a categorization of the kinds of resources that can be
generic entity. We finally propose a formal pattern for resource referenced on the web. We are confident that, based on this
modelling. categorization, it is possible to study the most suitable way
of handling the operational semantics that can be applied to
I. I NTRODUCTION different references.
The web is an information space realized by computation- The rest of the paper is organized as follows: in section I-A
ally accessible resources, each embedding some information, we discuss briefly the existing approaches to the problem of
which is encoded in some language, and expresses some identifying a resource on the web, in section II we discuss
meaning. One of the successful achievements of the web is the definitions of the concept of resource and its relation
that of allowing different parties of its global communities to the URI mechanism of identification that can be found
to share information [17]. Typically, typing an address in a in normative documents such as [4] and [17]. In particular,
web browser is enough in order to visualize or download an we underline the ambiguity of such definitions, showing the
object, the meaning of which can be then understood by a need for a rationale. Finally, in III we present the design
human agent. Such web address is a URI (Universal Resource rationale of IRE ontology, the most specific contribution of
Identifier) [4]. There is no doubt about the effectiveness of this paper. Section V summarizes the proposal underlining our
the URI mechanism for the referencing of resources that are contribution.
realized on the web.
Nevertheless, there is something more ambitious that the A. Related work
web is supposed to allow than just referencing web resources, The identification of resources is an important task to use
that is referencing things in general. That ambitious goal them on the web. Currently, there is a diffuse feeling that
requires a software agent to identify a resource unambiguously, the identification procedures suffer from a lack of consensus
in order to perform the appropriate operations on it. Tim about how to handle them. A typical example is the URI
Berners Lee et al. in [18] mention identification of resources http://www.w3.org: does it identify the web document that is
is essential for information sharing, interoperability, reasoning, placed at that web address, or the W3C organization? There
and elaboration in general on the web. The semantic web (SW) have been many proposals suggesting different approaches to
has as main goal that of make such scenarios possible. the aim of addressing the issue. In this section we briefly
Currently, URIs are used as the uniform mechanism for summarize some significant ones.
identifying heterogeneous entities, e.g., documents, metadata, Alistar Miles [26] describes his perception of the problem
ontologies, abstract concepts, physical things, events. But there by isolating a possible obstacle: the creation of a same
is no clear categorization of which are the possible ways to URI for representing different concepts. This has also been
identify and reference those entities on the web. This sort of named URI collision [17]. Miles proposes an interesting ’low
level’ approach as a best practice, that of using HTTP URIs II. URI AND RESOURCES
to address entities that are not accessible on the web. He The term “resource” is generally used for all things that
proposes to manage the problem at the server side by means might be identified by a URI [17].
of a negotiation on how to resolve the URI. For example, In literature, we find several definitions for the term “re-
if one creates the URI http://foo.com/me to describe him- source” used in the context of world wide web. In particular
self/herself, then it could be resolved by the server as the we quote here three authoritative documents, [4], [3], [17]1
URI http://foo.com/me.html or http://foo.com/me.xml or other, and discuss about the way and consequences of the definition
depending on a sort of configuration of the browser. they provide for “resource” . In [3] the concept of resource is
Steve Pepper [33] expresses a similar difficulty about the defined as follows:
use of URIs for identifying all kinds of entities. In particular, A resource can be anything that has identity. Fa-
he proposes to associate a resource to a document, whose miliar examples include an electronic document, an
content describes the subject of the resource (i.e., a subject image, a service (e.g., ”today’s weather report for
indicator). Nevertheless, this solution leaves the responsibility Los Angeles”), and a collection of other resources.
of interpreting the identity of a resource to a human agent, Not all resources are network ”retrievable”; e.g.,
and there is no way to ensure that the subject indicator refers human beings, corporations, and bound books in
to a single subject. a library can also be considered resources. The
Kendall Clark [7] discusses the ’tidiness’ of web specifica- resource is the conceptual mapping to an entity or
tions, and the importance to clarify the conceptual assumptions set of entities, not necessarily the entity which cor-
upon which the web is built, and the semantic web is going responds to that mapping at any particular instance
to be built. in time. Thus, a resource can remain constant even
David Booth [6] proposes an informal categorization of when its content—the entities to which it currently
what can be identified by a URI, suggesting the definition corresponds—changes over time, provided that the
of different conventions for each of the four uses he has conceptual mapping is not changed in the process.
identified. John Black [5] suggests to create a sort of machine- Moreover, in the same document the mechanism for identify-
oriented Wikipedia, machines that share knowledge through ing resources (i.e., URI) is specified, and it is also said that:
the construction of web sites such as del.icio.us [8].
Having identified a resource, a system may perform
Parsia and Patel-Schneider [31] deeply analyze the issue of a variety of operations on the resource, as might be
defining meaning in the SW. They propose to determine the characterized by such words as ‘access’, ‘update’,
meaning of a document as the result of an entailment. In this ‘replace’, or ‘find attributes’.
sense, “only documents explicitly mentioned in constructs like
The following definition of “resource” is given by [4], which
the OWL importing mechanism contribute to the meaning of
updates [3]:
that document.”
Another good suggestion comes from Pat Hayes [16] who This specification does not limit the scope of what
underlines the difference between access and reference. Both might be a resource; rather, the term ”resource”
are relationships between names and things, but they are is used in a general sense for whatever might be
inherently different and the fact that [17] does not distinguish identified by a URI. Familiar examples include an
between the two contributes to cause confusion. electronic document, an image, a source of infor-
mation with a consistent purpose (e.g., ”today’s
All these proposals are important contributions to solve the
weather report for Los Angeles”), a service (e.g., an
“identity crisis” but none of them provides a formal model,
HTTP-to-SMS gateway), and a collection of other
which could help in finding a comprehensive solution at
resources. A resource is not necessarily accessible
both syntactic and operational levels. The identity of entities
via the Internet; e.g., human beings, corporations,
referenced on the web is often intended as the location at
and bound books in a library can also be resources.
which a resource is placed; in other words, there is a need
Likewise, abstract concepts can be resources, such
for an explicit distinction between the identity of a resource
as the operators and operands of a mathematical
and its identifier. For example, recalling the W3C web site,
equation, the types of a relationship (e.g., ”parent”
the http://www.w3.org URI has its own identity as identifier
or ”employee”), or numeric values (e.g., zero, one,
(i.e., a string), the web location it is associated to has its own
and infinity).
identity as a place, the web document has its own identity
as a computational object (i.e., file), and the subject of the On the other hand, in [17] the concept of resource is used
document has its own identity (i.e., the W3C organization). with a twofold meaning: that of whatever might be identified
by a URI, and that of anything that can be the subject of a
Recently in the context of W3C working groups a work
discourse, such as cars, people etc. Furthermore, the concept
effort on how to embed RDF triples in HTML is being
of Information resources is defined as those resources which
conducted and there is already a working draft containing a
proposal for a syntax, namely RDFa [1]. RDFa complies to 1 Note that [3] has been replaced by [4] but we decided to quote and discuss
our approach although it does not cover all aspects. about it here because it is still used as reference from many web users
essential characteristics can be conveyed in a message. [17] different meanings associated to the term ’resource’, and con-
also defines the principle of opacity of a URI, which promotes textualize those meanings in a formal pattern. The definition
the independence between an identifier and the state of the of “resource” in [4] corresponds to that of concept “Entity”
identified resource. used in IRE. We reserve the name ’web resource’ to one
Given the above, at least four possible interpretations of the meaning, which seems more intuitive from a commonsense
intended meaning of the term “resource” emerge. Even though viewpoint, even though our principal aim is conceptual, not
it is not our principal aim, it could be useful to establish what terminological.
meaning is the most suitable in the web domain. III. T HE IRE ONTOLOGY
• computational object: if a resource is a computational As outlined above, the definitions of resource that can be
object, something on which one can perform operations found in literature [17], [3], [4] show ambiguity, making the
[3] - in this context we define “computational object” issue of handling the identification of a web resource very
such as (i) the physical realization of an information problematic.
object, (ii) something that can participate in a computa- Our approach restricts the nature of the web resource to that
tional process. Examples of computational objects are: a of a computational object. This choice is motivated by the fact
database, a digital document, a software application - then that a resource is something that has to be addressable, and
its identity would not be equivalent to a virtual localiza- things like cars and people are not addressable for their nature.
tion, because a computational object is a physical entity Hence, it is wrong in principle to use the same mechanism of
and realizes (is the support for) a certain information addressing for entities that have such different sorts. In [15]
object. Neither physical entities nor information objects IRE has been formalized in first order logic, here we approach
can be reduced to regions in a virtual space, especially if its formalization in OWL, and introduce two possible ontology
that space should be uniquely identifiable through URIs. design patterns for expressing IRE content.
For example, the personal home page of Aldo Gangemi
is a document which exists on the web and is reachable
through the dereferencing of its URI, but it does continue
to exist also if it changes its location or if the server it
is stored on becomes offline.
• conceptual mapping: if a resource is intended as a
“conceptual mapping” [3] then its identity is purely
formal. For this reason it cannot be also intended as
a “computational object”. As a conceptual mapping, a
resource can be characterized as a location in the virtual
space of the combinatorial regions that are identified by
the URIs. Consequently, the identity of a resource in this
sense is equivalent to a localization in that space. As a
matter of fact, without that space, it would not exist, and
its URI is sufficient to identify it unambiguously.
• proxy: considering the principle of opacity [17], the sense
of resource can be that of a ’proxy’ that is localized in a
region of the virtual space identified by the URIs. In this
case, the resource is actually intended as a computational
object, and its identity is given by the set of elements
composing the proxy. For example, an English text, a
picture, a metadata schema, etc. According to this mean-
ing of “resource”, its identity goes beyond its location. A
resource does exist beyond its location, and its identity
holds over its presence on the web.
• entity: by defining “resource” with the meaning of an Fig. 1. The IRE conceptual pattern
entity [4] - being it either a computational object or
not - is problematic because the relationship that holds
Figure 1 depicts the IRE (Identifiers, Resources, and Enti-
between a resource and a URI would be the same for
ties) conceptual pattern. It includes the main concepts related
addressing computational objects and physical or abstract
to resources and their identification.
objects. This approach is problematic, because it attempts
A Resource is a computational object that may have a web
to address entities (i.e., physical and abstract objects) that
location. We define a web resource as a resource that is placed
are not addressable in principle.
in one or more abstract web locations. In this sense to be a
Based on this rationale, we give a formal description of the web resource is a particular state of a resource. This means
that the identity of the resource is something that goes beyond about that entity. For example a document whose subject
its location. An abstract web location is a place (i.e., a point) of discourse is the entity that the resource is proxy for.
in the combinatorial regions that are identified by the URI • Formal exact proxy for: a relationship between a seman-
addressing mechanism (i.e., each URI identifies one and only tic resource and exactly one entity, where the semantic
one abstract web location) 2 . To this aim the datatype property resource is about that entity, and describes it by means
has identifier is specified as functional. Although we cannot of a semantic structure. For example, a set of metadata
directly address an entity that is not a computational object, associated to an individual from an OWL ontology.
we need to be able to assert facts about it on the web. We can We remark that the relations described above are mappable
do this by using a web resource whose functions as a proxy to already existing or proposed concrete solutions. As a proof
for that entity (i.e., a ProxyResource). In order to make the of concept of this claim, let’s consider the skos property
model clearer, we give a prose description for each element skos:subjectIndicator [27] and the topic maps el-
that has been defined: ement subjectIndicatorRef [24]. The web resource
• Abstract Web Location: a point in the combinatorial that is the value of such properties would function as a
regions identified by the URI metric. proxy resource for an entity, and this means that the two
• Resource: a computational object that can be composed properties are either approximate proxies or informal exact
of other resources (i.e., proper part of ). It might have proxies. Although this can be a way of identifying the entity of
a location (i.e.,Abstract Web Location), the address of interest, the interpretation of the content of the web resource
which is a URI. If the resource is a composed resource the remains a responsibility of a human agent. As a matter of
identifier of its abstract location is also an approximate fact, when expressed informally, there is currently no way to
identifier for its parts. automatically understand the meaning of the content of a web
• Web Resource: a resource that is associated with a web resource, with a decent precision. The situation is slightly
location, hence potentially accessible on the web. different if the web resource is a semantic resource. In that
• Proxy Resource: a web resource which functions as a case it functions as a formal exact proxy for an entity, and it
proxy for whatever entity (e.g., a personal home page, a is possible to enable a machine to derive the identity of the
set of metadata describing a person). entity of interest. For example, this is the case of a set of
• Semantic Resource: a web resource that realizes an metadata asserting facts about an individual of a given web
information object through a codification in a formal ontology, which a software agent could be able to perform
language for the web (e.g., OWL [21]) which functions some inferences on.
as a proxy for whatever entity.
A. An example: IRE pattern and Topic Maps
The IRE pattern from Figure 1 suggests a categorization of
the resources when their role is functioning as a proxy for an In order to give an example of the applicability of this
entity. Starting from this particular feature of a resource we approach also to techniques other than RDF, we informally
noticed that the relation proxy for can be of four types, and describe how to classify the Topic Maps concepts related to
that each of them can be treated in a different way. Each kind identity issues in terms of IRE. Based on [20]:
of proxy for relation may correspond to a different computa- ”..subject - anything whatsoever, regardless of
tional approach, or more specifically to a different operational whether it exists or has any other specific charac-
semantics associated to the resolution of the proxy’s URI. The teristics, about which anything whatsoever may be
four kinds of proxy relations can be described informally as asserted by any means whatsoever..”.
follows: The Topic Maps concept of “subject” is equivalent to that
• Resolvable proxy for: a relationship between a proxy of “Entity”. More precisely, the terms “subject” and “entity”
resource and a web resource where the proxy resource are synonyms. From the same document [20] we have the
allows the access to the web resource it is proxy for. For following definition of topic:
example, a ’href’ in a HTML document is a resolvable A topic is a symbol used within a topic map to rep-
proxy for the web resource it allows to access by clicking resent one, and only one, subject, in order to allow
the corresponding link. statements to be made about the subject through the
• Approximate proxy for: a relationship between a re- assignment of characteristics to the topic.
source and a collection of entities, where the resource is Based on IRE pattern a topic in a topic map is a formal exact
about some of those entities. In this case the resource proxy (i.e., a semantic resource) for a given entity. Again from
represents something within the collection, resulting in [20] we have the following definitions about identification of
approximate reference. entities:
• Informal exact proxy for: a relationship between a
”A subject indicator is an information resource that
resource and exactly one entity, where the resource is is referred to from a topic map in an attempt to
2 Notice that IRIs (Internationalized Resource Identifier) [19] are supposed
unambiguously identify the subject of a topic to a
to replace URIs in next future. Given this, IRIs involvement in the IRE pattern human being. Any information resource can become
is the same that URIs have. a subject indicator by being referred to as such
from within some topic map, whether or not it was The IRE ontology specializes or reuses the following predi-
intended by its publisher to be a subject indicator. A cates. For a complete axiomatization see the indicated URLs
subject identifier is a locator that refers to a subject and [22]. From DOLCE [10] IRE imports:
indicator. Topic maps contain only subject identifiers
dol:particular, dol:social-object,
(and not the corresponding subject indicators)....”
”...A subject locator is a locator that refers to the dol:region, dol:abstract-region,
information resource that is the subject of a topic. dol:time-interval, dol:proper-part-of
The topic thus represents that particular information dol:social-object v dol:particular
resource; i.e. the information resource is the subject
dol:region v dol:particular
of the topic... ”
In terms of IRE pattern, a “subject indicator” is a web resource dol:abstract-region v dol:region
which acts as approximate proxy for a given entity. In order to dol:time-interval v dol:region
identify an entity by a subject indicator, a human interpretation DOLCE ontology makes basic distinctions between objects,
is needed, and it is not guaranteed that such identification is events, and abstract entities. While objects and events like
unambiguous. Furthermore, a subject identifier is an abstract computers and software crashes are spatio-temporally local-
web location (i.e. a URI), which locates a subject indicator on ized, abstract entities like sets and value spaces have no
the Web. On the other hand, when the entity is addressed by a space-time (they are purely formal entities). DOLCE also
“subject locator”, it can be considered a computational object axiomatizes basic relations such as part and location-of.
available on the web, i.e., a web resource. From the DnS and Information Objects modules [34] the
IV. D ESIGNING IRE IN OWL imports are:
The IRE (Identity of Resources and Entities) conceptual edns:situation, edns:information-object,
pattern has been specified in first order logic in [15]. In order
edns:information-realization,
to make it available on the SW, we have expressed it in the
OWL(DL) language [30]. edns:formal-language, edns:method,
The following sections are organized as follows: in section edns:realizes, edns:about,
IV-A we present some reused and specialized predicates from edns:ordered-by, edns:involves.
other ontologies, in section IV-B we describe how we engi-
neered IRE in OWL showing two possible design approaches. edns:information-object v
The figures included in next sections are drawn by using UML
edns:social-object
notation and assuming an OWL profile. Specifically, UML
classes map to OWL classes, UML associations map to OWL
edns:information-realization ≡
object properties, and UML class attributes map to datatype
properties. We use a DL syntax notation for expressing axioms, dol:particular u
following [32]. ∃ edns:realizes.edns:information-object
A. Imported predicates in IRE
edns:method v edns:social-object
The IRE pattern specializes the DOLCE reference ontology
[9], [10], and some of its modular extensions, namely Spatial DnS and Information Objects ontologies make basic dis-
Relations, DnS with Information Objects, and Ontology tinctions between ’descriptive’ and ’ground’ entities, where
Design Ontology (ODO) modules. All modules have been the descriptive entities include social objects, like the ’student’
developed within EU projects Metokis [25], [2], WonderWeb or ’professor’ roles, the ’being active’ task, juridical persons,
[22], [12], and NeOn [28], and (including IRE ontology) are methods, and also information objects like the text of this
available in OWL at http://www.loa-cnr.it/ontologies/. For the paper. Descriptive entities have a lifecycle differently from
sake of readability we abbreviate the path pure information, which is an abstract entity.
“http://www.loa-cnr.it/ontologies” with Information objects have a core conceptual pattern, by which
“http://[*]” while the following prefixes are used in they are edns:ordered-by a representation language, they
the following definitions that correspond to the associated are edns:realized-by physical information realizations
namespaces: (physical objects, events, etc.), and can be edns:about any
other entity. Situations are reifications of states of affairs i.e.,
reifications of n-ary relationships.
xsd = http://www.w3.org/2001/XMLSchema# From the ODO module [35] IRE imports:
dol = http://[*]/DOLCE-Lite.owl#
edns = http://[*]/ExtendedDnS.owl# od:computational-object
inf = http://[*]/InformationObjects.owl# od:computational-object v
od = http://[*]/OD/OntologyDesign.owl# edns:information-realization
The OD ontology specializes the Information Objects
ontology in order to build a conceptual schema for
digital and analog content to be exchanged during
collaborative activities for ontology design. The
concept od:computational-object specializes
edns:information-realization for the
computational world. Any physical document, electronic
service, file, application, etc. are considered here
computational objects.
B. OWL IRE
IRE express concepts about “referencing” and “accessing”
of a web resource, according to [16].
Fig. 3. IRE with binary relations
is implicit. In particular we introduce the following object
properties:
• ApproximateProxyFor: is an object property having
WebResource as its domain, and dol:particular
i.e., any entity, as its range. We define a cardinal-
ity restriction on WebResource for this object prop-
erty. More specifically, for a web resource to be
an approximate proxy for, it has to be related with
at least two dol:particulars by means of the
Fig. 2. The IRE taxonomy
approximateProxyFor object property
• ExactProxyFor is an object property having
Figure 2 shows the OWL classes that we have defined WebResource as domain and dol:particular i.e.,
in order to express the foundations of IRE. Specifically, a any entity as range. We define a cardinality restriction on
WebResource is a computational object that have at least WebResource for this object property: a web resource
one assigned web location i.e., AbstractWebLocation. can be an exact proxy for only one dol:particular
An AbstractWebLocation is an abstract region • FormalExactProxyFor is a subproperty of
i.e., dol:abstract-region, a place in the combinatorial exactProxyFor, where the domain is restricted
space identified by URIs. A SemanticWebResouce is a to SemanticWebResource
web resource that is represented i.e., dol:realized-by • ResolvableProxyFor is an object property where the
with a formal language for the SW e.g., OWL. The class domain is Anchor, and excludes WebResource.
Anchor represents computational objects that are embedded Anchor has a universal restriction on this object property
in web resource and that may allow access to web resources that restricts the range to WebResource, and a cardi-
through a ResolutionMethod, e.g., an HTML link. nality restriction “equal to 1”: an anchor is a resolvable
The core of IRE theory is in the proxy relations between proxy for one and only one web resource
resources and entities of the world. Those relations are tem- • ProxyFor is an object property having
porally indexed i.e. a resource is a proxy for a certain entity od:computational-object as domain and
at some time. We identified two possible design patterns dol:particular as range. All previously defined
to represent that in OWL: the first treats temporal aspects object properties are subproperties of this one.
explicitly by reifying the relation with the n-ary relation
D. IRE with situations
pattern [29], [11], while the second treats temporal aspects
as implicitly assumed by binary relations. In this section we In this section we show how to represent IRE by means
show these two ontology design patterns for IRE. of edns:situation [14]. Situations (i.e., instances of
edns:situation) are reifications of states of affairs i.e.,
C. IRE with binary relations reifications of n-ary relationships. This approach is compliant
Figure 3 shows IRE in OWL. The figure depicts the taxon- to the n-ary relation pattern suggested by [29], for which it
omy introduced in IV-B, and the object properties expressing provides an explicit vocabulary and general axioms. Situations
the proxy for relation kinds. In this case the time aspect allow us to explicitly treat temporal indexing. Referring to
We have singled out some ambiguities that could prevent
successful solutions to the web identity crisis., and proposed
a way to clarify and formalize the different meanings of
resources in a unique modelling framework. Finally, we have
suggested some extensions to the model that can help classi-
fying syntactic and operational solutions, and verifying their
completeness and consistency.
Currently, URIs are used as the uniform mechanism for
identifying heterogeneous entities, e.g., documents, metadata,
ontologies, abstract concepts, physical things, events. But there
is no clear categorization of which are the possible ways to
Fig. 4. IRE with n-ary relations
identify and reference those entities on the web. We support
the use of a formal model for the categorization of entities that
can be referenced on the web. To this aim, we have defined
section III, the proxy for relation is intended as the “situation” IRE (Identifiers, Resources, and Entities), a conceptual pattern
for a web resource to “being a proxy for some entity at a based on an ontology of Information Objects [2], built on
given time”, while the addressing of a web resource, which top of DOLCE and on some of its modular extensions [23],
potentially allows its accessing, is intended as the “situation” [13], [12], [22]. In [15] we formalized IRE with first order
for a web resource of “having a web location at a given logic, while here we have proposed an OWL ontology based
time”. Figure 4 depicts the IRE design pattern in terms of on those formal definitions. IRE describes “referencing” and
this engineering approach. More specifically, we define the “accessing” of a web resource according to [16]. We have
following relation classes: shown in this paper that there are two ways of engineering
• WebLocationState: is a situation of a web resource that IRE in OWL. The first provides an ontology pattern based on
is associated to a point in the combinatorial regions binary relationships, the way OWL natively allows to express
identified by the URI metric i.e., a web location, at a relations, and the second provides a pattern based on reification
given time. of n-ary relations according to [29], [14]. The latter pattern
• ProxyFor: a situation of a web resource which functions allows us to also express temporal indexing.
as a proxy for whatever entity (e.g., a personal home
ACKNOWLEDGMENT
page, a set of metadata describing a person), at a given
time. We are grateful to the members of the NeOn consortium
The kinds of proxy situations can be informally described who contributed to the NeOn vision being funded by the
as follows: European Commission 6th IST Framework Programme. Fur-
ther information on NeOn is available on http://www.neon-
• ApproximateProxyFor: a relationship between a re-
project.org.
source and more than one entity at a given time, where the
resource is about those entities. In this case the resource R EFERENCES
represents all the entities approximately. [1] B. Adida and M. Birbeck. RDFa Primer 1.0 Embedding RDF in
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