Contextual Semantic Search Navigation

Search has for a long time been an important tool for users seeking information. Manypopular search systems have been based on keyword search. However, such systems arenot that well adapted to explore the search space. Effective exploration requires systemswhich can guide the user in his quest. The main focus of this thesis is to generate a framework for semantic navigational searchwhich is compatible with the vector space model and unites formal and informal seman-tics. In this thesis, formal semantics is represented by ontologies, while informal seman-tics is represented by folksonomies. The research conducted has been divided into four main phases with different foci that to-gether fulfill our research focus: (i) Formal semantics, (ii) Informal semantics, (iii) Struc-ture verification, and (iv) Contextual semantic search navigation. In the first phase, thefocus was ontologies and extending concepts with concept signatures. A concept signa-ture is a shallow semantic representation of a concept based on how the concept is referredto in textual documents bridging the semantic and syntactic representation of concepts.The second phase focused on structuring folksonomy tags and extending tags with con-cept signatures. This phase also focused on consolidating the tag vocabulary. These twophases together unify formal and informal semantics with a common format. The thirdphase developed an approach for assessing the hierarchical relations of ontologies andstructured folksonomies based on concept signatures. Finally, the fourth research phasedeveloped an approach to contextual semantic search navigation based on a hierarchicalmodel and concept signatures. The approach is based on semantic navigators which usethe concept signatures actively to generate and rank navigation suggestions to the user.Several experiments have been conducted to evaluate the proposed approaches, and theyshow promising results. The main contributions of this thesis can be summarized as follows: • A semantic representation which unifies formal and informal semantics.• An unsupervised approach to identifying semantic similarity in tags.• An approach to contextualizing semantic navigators for search using tag signaturesand hierarchical relations. • An approach to evaluating the taxonomic quality of ontologies and folksonomies.• An approach to generating concept signatures from formal semantics (ontology).• An approach to generating concept signatures from informal semantics (folkson-omy).