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11.2.1 EDOAL

The Expressive and Declarative Ontology Alignment Language EDOAL http:alignapi.gforge.inria.fredoal.html allows for representing correspondences between the entities of different ontologies. Unlike other formats, the alignment vocabulary allows the representation of complex correspondences allowing precise description of the relation between entities. The alignment vocabulary extends the alignment format. Representing ontology alignments is the general purpose of this vocabulary. Particularly, it extends the ontology alignment format in order to enable the representation of complex correspondences. This format can be used for cases where expressing equivalence or subsumption between terms is not sufficient and more precise relations need to be expressed. While term equivalence or subsumption might be enough for exchanging documents, more precise relations are needed to exchange and integrate data. This vocabulary was originally designed with the goal of representing patterns of correspondence between ontologies. Since then the vocabulary was both simplified and extended to obtain a minimal vocabulary on top of the alignment format, thus providing the ability to express all possible kinds of ontology alignments. The alignment vocabulary has the following features: ฀ Construction of entities from other entities can be expressed through algebraic operators. Constructed entities allow overcoming the shallowness of some ontologies. ฀ Restrictions can be expressed on entities in order to narrow their scope. Narrowing the scope of an entity makes possible to better align this entity with the one corresponding in the other ontology. ฀ Transformations of property values can be specified. Property values using different encoding or units can be aligned using transformations. The current version of EDOAL only supports limited transformations. This will be improved soon. ฀ Linkkeys can be defined for expressing conditions under which, instances of the aligned entities should be considered equivalent. In the alignment format, an alignment is a set of cells, each cell being a correspondence between two entities. The alignment vocabulary extends this scheme by allowing cells to contain compound entity descriptions. Each entity can be typed according to one of the following category: Class, Instance, Relation, Property. A relation corresponds to an object property in OWL, a property to a datatype property. Each entity can then be restricted, and transformation can be specified on property values.