多媒體網路安全實驗室 Combining ontological profiles with context in information retrieval Date:2012.03.06 Reporter : Hong Ji Wei Auther : Geir Solskinnsbakk and Jon Atle Gulla 出處: Data & Knowledge Engineering,vol 69, no 3, 2010, pp 251–260 多媒體網路安全實驗室 Outline 1 Introduction 2 Related Work 3 Ontological profiles 4 Construction of ontological profiles 35 Experiment 46 Context 37 Conclusions 2 多媒體網路安全實驗室 Introduction An ontology is a formal conceptualization of a domain,specifying the concepts of the domain and the relations between them. 大體而言,本體論的兩大重點: 1.以已經定義的字彙名詞(vocabulary of terms) 來描述以存在的實體(entity) 2.以一定規格(specification)表示出這些實體間 的關係(relationship)與存在的意義(meaning) 3 多媒體網路安全實驗室 Early semantic search engines tried to use ontology concepts and structures as controlled search vocabularies,but this was unpractical both functionally and usability perspective. Ontological profile=Ontology and concept characterizations. 4 多媒體網路安全實驗室 Related Work Su describes in a method for ontology mapping, based on an extension of the ontology. Tomassen describes an ontology driven information retrieval system based on extending ontologies. Sieg et al describe an approach for representing user context for search. 5 多媒體網路安全實驗室 Ontological profiles An ontological profile is an extension of a domain ontology. The ontology is extended with semantically related terms that are added as vectors for each of the concepts of the ontology. The concept vector can be viewed as an extended semantic characterization of the concept, reflecting the semantics of the concept in the document collection. 6 多媒體網路安全實驗室 therefore argue that the ontological profile may be better suited: (i) a specific document collection (ii) the vocabulary in the documents (iii)the use of the ontology concepts in the documents. EX: 7 多媒體網路安全實驗室 8 多媒體網路安全實驗室 Construction of ontological profiles Construction of the ontological profile is based on three important aspects: 1. Statistics: Apply statistical techniques to the document collection by counting the frequency of the terms in the documents 2. Linguistics:the terms of the documents, namely stemming, to collapse certain semantically similar terms into a single form. 3. Proximity:Apply a proximity measure to the cooccurrence of concept names and terms 9 多媒體網路安全實驗室 10 多媒體網路安全實驗室 Experiment The process consists of two steps: (i) query interpretation 1. Simple query interpretation • This is the most basic strategy for query interpretation 2. Best match query interpretation • • In contrast to the simple query interpretation During interpretation of the query we try to recognize the connection between the query terms by mapping the terms collectively to a single concept 11 多媒體網路安全實驗室 3. Cosine similarity query interpretation • we are not able to directly recognize the relation from the query terms. • Try to recognize relations between the concepts that the query terms map to via the ontological profile. 4. Ontology structure query interpretation • The measure we use is based on the distance between the concepts in terms of relations. • by generating a graph representation of the ontology, in which nodes represent concepts and edges represent relations.(to find the distance for each pair of concepts) 12 多媒體網路安全實驗室 (ii)Query expansion The query expansion process reformulates the original query by adding semantically related terms to the query. The weight of the original query terms are boosted to reflect their importance. The motivation behind adding these terms is to remove some of the noise introduced by the increased set of query terms. 13 多媒體網路安全實驗室 Experimental data and results 14 多媒體網路安全實驗室 Context Context is the set of suitable environmental states and settings concerning a user. Attributes are context if they are non-essential (for tasks). We can thus conclude that only non-essential information used to enhance the applications computations can be considered context. 15 多媒體網路安全實驗室 1. Search context Definition. Search context is the context of a user posting queries to a search application. We can partition the systems knowledge about the user into two separate parts: The first is of course the query The second part is additional knowledge which can characterize the situation of the user(i.e., the context.) 16 多媒體網路安全實驗室 2. Contextualized ontological search Ontology Profiles FQV UQn CQun ( 1) 17 多媒體網路安全實驗室 Conclusions The ontological profile describes each concept as a vector of terms with weights describing the strength of the relation between them. We defined search context and discussed how contextual search may be incorporated into our semantic search approach 18 多媒體網路安全實驗室
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