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TopDynamic Taxonomies
Dynamic taxonomies (Sacco, 2000, later also called faceted search systems) are a general knowledge management model based on a multidimensional classification of heterogeneous data items and are used to explore/browse complex information bases in a guided yet unconstrained way through a visual interface. The reader is addressed to Sacco and Tzitzikas, 2009, for the most complete and up-to-date book on this model.
The intension of a dynamic taxonomy is a taxonomy designed by an expert. This taxonomy is a concept hierarchy going from the most general to the most specific concepts. A dynamic taxonomy does not require any other relationships in addition to subsumptions (e.g., IS-A and PART-OF relationships). Directed acyclic graph taxonomies modeling multiple inheritance are supported but rarely required.
Key Terms in this Chapter
Extensional Inference Rule: Two concepts A and B are related iff there is at least one item d in the knowledge base which is classified at the same time under A (or under one of A’s descendants) and under B (or under one of B’s descendants).
Shallow Extension: Of a concept C, denotes the set of documents classified directly under C.
User Focus: The set of documents corresponding to a user-defined composition of concepts; initially, the entire knowledge base.
Multidimensional Taxonomy: Taxonomy where an item can be classified under several concepts.
Subsumption: A subsumes B if the set denoted by B is a subset of the set denoted by A (B ? A).
Reduced Taxonomy: In a dynamic taxonomy, a taxonomy, describing the current user focus set F, which is derived from the original taxonomy by pruning from it all the concepts not related to F.
Monodimensional Taxonomy: Taxonomy where an item can be classified under a single concept only.
Zoom: A user interface operation, that defines a new user focus by OR’ing user-selected concepts and AND’ing them with the previous focus; a reduced taxonomy is then computed and shown to the user.
Deep Extension: Of a concept C, denotes the shallow extension of C union the deep extension of C’s sons.
Taxonomy: A hierarchical organization of concepts going from the most general (topmost) to the most specific concepts. A taxonomy supports abstraction and models subsumption (IS-A and/or PART-OF) relations between a concept and its father. Tree taxonomies can be extended to support multiple inheritance (i.e., a concept having several fathers).
Facet: One of several top level (most general) concepts in a multidimensional taxonomy. In general, facets are independent and define a set of “orthogonal” conceptual coordinates.