= Definition: SimilarityMeasure =

The concept of a SimilarityMeasure in the PhaseLibs describes an interface to measure a distance (of any kind) between two ontology entities ([wiki:Frame Frames]). These entities can be taken from the same, or from two different ontologies. The resulting value is rquired to be in the interval [0..1].

A SimilarityMeasure can use any information available (i.e. accessible via the ontology model interface) about the given entities ([wiki:Frame Frames]). Furthermore a SimilarityMeasure can calculate a matrix of similarities to enable the algorithm to work more efficiently on large batches.

This basic concept is represented by the interface [http://phaselibs.opendfki.de/repos/trunk/PhaseLibs/doc/JavaDoc/de/dfki/km/phaselib/model/evidence/SimilarityMeasure.html de.dfki.km.phaselib.model.evidence.SimilarityMeasure].


= Extended Concepts =

In order to allow for more specific information to be gathered from the algorithms, several extensions of this SimilarityMeasure concept exist.

== asymmetric SimilarityMeasure ==

There is the concept of the asymmetric SimilarityMeasure, which allows the values of similarity(entityA, entityB) and similartiy(entityB, entityA) to be different. It is represented by the interface [http://phaselibs.opendfki.de/repos/trunk/PhaseLibs/doc/JavaDoc/de/dfki/km/phaselib/model/evidence/AsymmetricSimilarityMeasure.html de.dfki.km.phaselib.model.evidence.AsymmetricSimilarityMeasure]. This interface extends the [http://phaselibs.opendfki.de/repos/trunk/PhaseLibs/doc/JavaDoc/de/dfki/km/phaselib/model/evidence/SimilarityMeasure.html SimilarityMeasure] by methods to query this directed similarity, leaving the old methods to some sort of joint similrity, to be calculated from the two directed ones. A common approach to this calculations would be the minimum of the two similarities.


== extended SimilarityMeasure ==

Furthermore, there are algorithms (like [wiki:similarity_SimFlood SimilarityFlooding]) that additionally provide information about a dissimilarity of entities. To allow for such information, the interface [http://phaselibs.opendfki.de/repos/trunk/PhaseLibs/doc/JavaDoc/de/dfki/km/phaselib/model/evidence/ExtendedSimilarityMeasure.html de.dfki.km.phaselib.model.evidence.ExtendedSimilarityMeasure] requires methods for dissimilarity querying.