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In the literature, ontology change management systems (OCMS) are direct implementation of the concept of “change management” stated by reference (Klein, 2004). Ontology change management combines ontology evolution and versioning features to manage ontology changes and their impacts. Since 2007, many works have combined ontology evolution and versioning into ontology change management systems (OCMS). The evolution subject has been massively studied in these works. They especially addressed the consistence issue for the application of changes on the ontology. These proposals constituted a consequent background for ontology change management but they did not take into account certain specificities of ontologies.
One of them is the fact that ontologies are decentralized data Rajugan (2006). It means that multiple versions of the same ontology evolution are bound to exist over the Web and must be supported. It implies that ontology chronological evolution is not enough to manage ontologies. Actually, managing different parallel versions of a same ontology would bridge this gap.
Another characteristic is that ontologies are meant to grow during their lifecycle and may become too large to be used in its original scale by potential applications. Indeed, ontology development implies a dynamic and incremental process starting from the creation of a brute ontology, which has to be revised and refined (Djedidi, 2009). Refinement often leads to the improvement of the ontology level of detail corresponding to the addition of new elements to its conceptualization. Therefore the ontology size may increase after each refinement iteration, with no guaranty that the ontology is still manageable by applications and understandable by humans.
In the literature, ontology views have been defined to bridge this ontology size issue and improve ontology reusability. Several definitions and implementations of ontology views have been studied in the Ontology View Management specific research field. However no agreement was found. Nevertheless, a view generally is a subset specification on an ontology, which allows to extract a manageable portion of the ontology capable to be used and queried by applications like the whole ontology. The resulting sub-ontology can be generated not only as a sub-graph of the ontology but also as an independent ontology, itself being a new interpretation of the domain. It can be considered as a new parallel version of the actual ontology validating the decentralized quality of ontologies. From the different approaches studied in this chapter, can be deduced four types of view specification and implementation: query language based, subset extraction based, rule based and other views specifications based on hybrid techniques.
This chapter aims at giving an overall state of the art on ontology views, their objectives, their different implementations and use, the corresponding advantages and lacks, and finally defining the future research directions to take in the context of Ontology Change Management.
Key Terms in this Chapter
Resource Description Framework (RDF): Is a language for representing information about resources in the World Wide Web. It is particularly intended for representing metadata about Web resources, such as the title, author, and modification date of a Web page, copyright and licensing information about a Web document, or the availability schedule for some shared resource. SPARQL.
Ontology: Represents knowledge as a set of concepts within a domain, and the relationships among those concepts. It can be used to reason about the entities within that domain and may be used to describe the domain.
Ontology Change Management: Process of performing the changes as well as to the process of coping with the consequences of changes.
Web Ontology Language (OWL): Is a family of knowledge representation languages for authoring ontologies. The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web.
Uniform Resource Identifier (URI): Is a string of characters used to identify a name or a web resource. URI references are used for naming all kinds of things in RDF.
Ontology Evolution: Timely adaptation of an ontology to the arisen changes and the consistent management of these changes.
Database View: In database theory, a view consists of a stored query accessible as a virtual table in a relational database or a set of documents in a document-oriented database composed of the result set of a query or map-and-reduce functions. Unlike ordinary tables (base tables) in a relational database, a view does not form part of the physical schema: it is a dynamic, virtual table computed or collated from data in the database.
Materialized Database View: A materialized view is a database object that contains the results of a query. For example, it may be a local copy of data located remotely, or may be a subset of the rows and/or columns of a table or join result, or may be a summary based on aggregations of a table's data.
Ontology Mapping: Task of relating the vocabulary of two ontologies that share the same do main of discourse in such a way that the mathematical structure of ontological signatures and their intended interpretations, as specified by the ontological axioms, are respected.
OWL-DL: Is designed to provide the maximum expressiveness possible while retaining computational completeness, decidability and the availability of practical reasoning algorithms. OWL DL includes all OWL language constructs, but they can be used only under certain restrictions.