In the last few years, a lot of effort has been paid to support both consensus and heterogeneity in the same ontology. As a result, multiviewpoints ontologies have become essential for heterogeneous organizations and for diverse user communities that need to share and exchange information in an application domain. The development of multi-viewpoints ontologies by different communities makes distributed and heterogeneous knowledge resources not accessible. So, to solve this problem and in order to support users in sharing and reusing vocabularies and knowledge, we need for techniques for solving heterogeneity problems between different multi-viewpoints ontologies. In this case, multi-viewpoints ontology alignment is required to provide a consensual understanding of that domain represented by these ontologies. In the literature, there are much alignment systems, but existing systems are not capable to support multiple viewpoints. So, our challenge is to introduce the notion of multiple viewpoints in the alignment process. Therefore, in order to align multiviewpoints ontologies, we present in this paper first, the definition of multiviewpoints ontology in description logics extended by a stamping mechanism, and then we deal with their alignment problems and definitions.
Ontologies can apprehend, capitalize, represent, operate and share semantically
knowledge and information. However in reality, there are usually several ways to
capture the knowledge of a given domain, that is to say different viewpoints (or
perceptions) by which this knowledge can be represented. Thus, the same domain may
have more than one ontology, where each one is described according to a viewpoint
or a particular perception. Indeed, in a large organization, there may be several
communities or groups of individuals with their own viewpoints. These viewpoints
depend on the type of person (occupation, age, educational level, experience …) or use
(the same person may have different views depending on the task which he is trying
to accomplish) [
The two concepts ontology and viewpoint are complementary [
The exploration of multi-viewpoints ontologies [
An ontology alignment is defined as a set of correspondences between ontological
entities, i.e. classes, properties, and individuals, of two ontologies [
Therefore, the objective of this work is to find an alignment definition of the multiviewpoints ontologies described in description logics extended by a stamping mechanism, and to find a definition of the semantics of these alignments. The aim of these definitions is to be able to align multi-viewpoints ontologies.
The rest of the paper is organized as follows. Section 2 presents a multi-viewpoints ontology. In section 3 we detail syntax and semantics of multi-viewpoints ontology described in description logics extended by stamping mechanism. Section 4 looks at the problems of the multi-viewpoints ontology alignment. In section 5 we present a set of definitions for the multi-viewpoints ontology alignment, and Section 6 concludes with the future directions of work. 2 2.1
Definition of Multi-Viewpoints Ontology (MVp Ontology)
Viewpoint Approach
For a given domain of knowledge, several criteria can be used to observe an object.
These different perceptions of the world are called viewpoints or perspectives. In
computer science, most of data modeling systems don’t deal with the variety of
perceptions related to the same universe of discourse, and develop tools to create a single
model for a single vision of the observed world. The viewpoint approach is opposed
to this monolithic approach and makes it possible to model the same reality according
to different points of view [
The viewpoint approach is constructed on the conjunction actor/information.
Therefore, it is necessary to include the actor in the action. In [
Multi-Viewpoints Ontology
A multi-viewpoints ontology is defined as an ontology in which a concept can have
multiple definitions, each definition corresponding to a particular viewpoint on the
concept [
In [
The accepted definition in our work is that mentioned in [
A Multi-Viewpoints Ontology in Description Logics Extended
by a Stamping Mechanism
Description logics (DL) [
Definition 1 (Multi-viewpoints Ontology in Description Logics Extended by a Stamping Mechanism). A multi-viewpoints ontology described in description logics extended by a stamping mechanism is a multiple descriptions of the same universe of discourse according to different viewpoints. It is defined as the quadruple , , , where: : is a set of global concepts, : is a set of global roles, : is a set of bridge rules and : is a set of viewpoints, where a viewpoint is a partial description of a universe of discourse in a particular perception. It is defined by the triplet , , , where: : is a set of local concepts, : is a set of local roles and : is a set of local individuals. Definition 2 (Syntax of a Global Concept). Given , … , , … , a set of viewpoints. A global concept can be formed using the Boolean manufacturers (conjunction, disjunction) and the following global restrictions manufacturers: • •
,…., . , ,…., . connected by the role ,
,…., . , ,…., . of the role in the viewpoints : defines a new concept that all their instances are
: specifies the minimum or maximum cardinality
. ,
. a local Role, Definition 3 (Syntax of a Local Concept). Given . A local concept : is either a primitive local concept or a defined local concept: : . .
. , , … , where and are local concepts, , … are individuals, and is a natural number. is ,
° Definition 4 (Syntax of a Local Role). A given local role : is defined as: : , , where is the name of the local role defined in the viewpoint , are two local concepts defined in this viewpoint . As well, a local role can be a primitive local role or a defined local role: , , , and , where are given local roles.
Definition 5 (Syntax of a Global Role). A global role is defined as: : , : , where is the name of the global role, are two local concepts defined in two different viewpoints. As well as a local role, a global role can be a primitive or a defined global role.
Definition 6 (Syntax of a Subsumption Relation). Below a viewpoint , a local hierarchy / , is defined as a triplet , , where: is a set of local concepts, is a function of in , witch associated for all root concept denoted of a global concept of , and is the subsumption relation used to express explicitly a direct order relationships as follows: • •
: viewpoint
: and
, where : and .
, where is the most general concept defined in the viewpoint is a global concept. are two local concepts defined in the same Definition 7 (syntax of a Bridge Rule). We distinguish: • Inclusion. : : . It expresses the set inclusion between a local concept extension of a viewpoint and another concept of another viewpoint. • Inclusion with Multiple Sources. : … : .It expresses an inclusion relation between a list of local concepts belonging to several viewpoints and another destination concept belonging to another viewpoint. • Bidirectional Inclusion. : : . It expresses equality between two local concepts belonging to two different viewpoints. • Bidirectional Exclusion. : : . It expresses a relationship between two local concepts belonging to two different viewpoints. 3.1
Semantics of Multi-Viewpoints Ontology
In [
∆ Definition 8 (Local Interpretation). A local interpretation ∆ , . ), is associated for each local element, where ∆ is a domain of local interpretation and . I is a local interpretation function such that for all local concepts of , ∆ , , for all local , and for all individuals , ∆
.
∆ , for all global role Definition 9 (Global Interpretation). A global interpretation ∆ , . ) is associated for each global element, where ∆ ∆ … ∆ … ∆ is a domain of global interpretation and . is a global interpretation function such that for all global concepts , , ∆ .
Definition 10 (Domain Relation). A relation domain defines how two different viewpoints interact. 4
The problems of Multi-Viewpoints Ontology Alignment In this work, we will take into consideration the notion of viewpoint in the alignment process. Thus, the multi-viewpoints ontologies alignment is the task to find the relationships that hold between the entities belonging to these ontologies.
Multi-viewpoints ontologies cover different domains that can be modeled differently and can represent several viewpoints. They can support both heterogeneity (at a local level) and consensus (at a global level). In the multi-viewpoints ontologies alignment, there is a great heterogeneity resides in the variations present in the semantic coverage of comparable concepts, especially local concepts that are defined according to different viewpoints and that can be semantically very similar. Indeed, the mapping task or alignment task between multi-viewpoints ontologies is more difficult than that between classical ontologies, because there is much specificity for this process. Among the specificities of multi-viewpoints ontologies alignment, we may find:
In the alignment process between classical ontologies, the task is to discover correspondences between concepts, properties and individuals. In our context of multiviewpoints ontologies described in description logic extended by stamping mechanism, it is necessary to take into account the different types of concepts (global and local), the different types of roles (global and local), individuals. 4.2
Localization of Local Elements According to the Different Viewpoints In our context, there are two description types: a global description and other partial descriptions defined according to different viewpoints. So, taking into account the localization of the local concept (local role) in the alignment process influenced on the remaining correspondences that can be discovered. 4.3
The consideration of bridges rules between elements of different viewpoints impact on the set of correspondences found. 5
We adopt the definitions of classical ontology alignment presented in [
Definition 11 (MVp Ontology Alignment). Given , two multiviewpoints ontologies in description logics extended by a stamping mechanism. An alignment between , is defined as the task to find the best subset of the correspondences between multi-viewpoints ontology elements belonging to and .
Definition 12 (MVp Ontology Element). A multi-viewpoints ontology element is a term of the multi-viewpoints ontology (e.g., global concept, local concept, global role, local role or individual).
Definition 13 (Correspondences). Given , ′ two multi-viewpoints ontologies in description logics extended by a stamping mechanism, a correspondence between , ′ is defined as a triple , ′ , where: and are multi-viewpoints ontology elements from the two multiviewpoints ontologies to align, and is a relation that is asserted to hold tween ′
Multi-viewpoints ontologies alignment contains correspondences between global concepts, local concepts, global roles, local roles or between individuals belonging to these ontologies. These correspondences are similar to the bridge rules in a same multi-viewpoints ontology. We can identify the different types of correspondences between two multi-viewpoints ontologies i and j as follows: i: CG j: DG , i: RG j: SG , i: RL j: SL , i: RL j: SG , i: CG i: CL i: CL i: a
j: DG , i: RG j: SG , i: RL j: SL , i: RL j: SG , i: a j: CG , i: a j: CL , j: b , where CG and DG are global concepts, CL and DL are local concepts, RG and SG are global roles, RL and SL are local roles, a and b are individuals, is a subsumption relation , is a disjunction relation , is a membership relation, and is a identity relation.
Consequently, a multi-viewpoints ontology alignment involves a set of entities connected by symbols of relations. It is seen as a pair , , where is a set of entities described in description logics extended by a stamping mechanism. And is a set of symbol of relationships between these entities. So, it is necessary to interpret the pair , before interpreting a multi-viewpoints ontology alignment.
j: DG, i: CL j: DG , i: CL j: DL, j: DL , Definition 14 (Entities Interpretation). Interpretation of entities is a pair ∆ , . ), where ∆ is a domain of interpretation and . is an interpretation function such that for all local concepts , ∆ , for all global concepts , ∆ , for all local roles , ∆ ∆ , for all global roles , ∆ ∆ , and for all individuals , ∆ , where∆ is a local domain of interpretation and it is a subset of ∆ . Definition 15 (Multi-Viewpoints Ontologies Alignment Interpretation). In our context, all entities are coming from the same description language. An interpretation of an alignment relation between two multi-viewpoints ontologies is a pair ∆ . , . ), where ∆ is a global domain of interpretation and . is a binary relation of interpretation such that for all relations , ∆ ∆ , where ∆ and ∆ are domain of interpretation of the multi-viewpoints ontologies respectively, and are subsets from∆ . Each multi-viewpoints ontology has its own domain of interpretation. 6
In this paper, we specified the basic concepts that constitute a starting point for multiviewpoints ontology alignment.
Several research directions are considered to carry out this work. We will use these definitions to propose a method of multi-viewpoints ontology alignment. We, also, plan to include bridge rules between multi-viewpoints ontologies elements for the reasoning on the multi-viewpoints ontologies and alignments in order to obtain the best set of alignments between these ontologies.