Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Ontology change management

When ontologies are used as means for describing knowledge about information on the web, we will have a situation in which not only the information on the web changes continuously, but also the knowledge that is used to interpret it. Changes in the ontologies will possibly have effects on the validity of tasks performed with it.

We propose a framework for coping with change in distributed ontologies. The framework consists of two major elements. The first element is a language for representing ontology change. For this, we defined a taxonomy of change operations.

Because it is influenced by the expressivity of the ontology language considered, the set of operations is to some extent language specific. We derived the set by iterating over all the elements in the meta-model of the ontology language, creating "add", "delete" and---when appropriate---"modify" operations for all elements. In this way, we abstracted from representational issues and had a guarantee that we covered all possible modifications. To decide on which language we would base our change representation, we compare two well-known knowledge representation formalisms: the OKBC knowledge model and the OWL (Full) ontology language. By comparing their respective knowledge models, we conclude that strictly speaking neither of these is a subset of the other. However, it appears that the things that are not present in OWL are quite rare in practice. Therefore, we decide to use OWL as basis for our change operations.

In addition to the operations that are directly derived from the knowledge model of the ontology language, we also introduce complex operations. These operations can be used to group together several basic operations, and/or to encode additional characteristics of the change operations. Operations that cluster other operations can be used when the constructing operations form a logical unit (e.g. removing something and adding it somewhere else), and when the composite effect of operations is different from the effect of operations on their own. Operations that encode additional knowledge can be used to define specialized variants of other operations, e.g. an operation that specifies that the range of a property is restricted instead of just modified. Complex operations are useful for both visualizing and understanding changes and for determining their effect. The possibility to define complex changes forms an extension mechanism that allows for task- or domain-specific representations of change.

The framework consists---besides a representation for changes---also of an abstract process model for ontology change management.

Basically, this model describes the following steps:
- Change information should be created from the sources that are available,
- Heuristics, algorithms or human input should be used to enrich this information (e.g. resulting in a set of change operations), and
- Ontology evolution related tasks can be performed with help of the enriched change information.

We jointly developed two tools that can be used to create change information. We also specify several processes for deriving new information from existing change information. In addition, we describe how to perform four ontology evolution related tasks.

First, we explain how we can use an ontology to access or interpret instance data of another version of the ontology.

Second, we describe a procedure that heuristically determines the validity of mappings between ontology modules. This procedure predicts whether subsumption reasoning within one module is still valid if changes have occurred in an ontology from which concepts or relations are imported.

Third, we adapt a methodology for the synchronization of related, but independently evolving ontologies to be used within our framework.

Finally, we show a tool that visualizes changes at an abstract level to help people with understanding these.

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