2/10/2016Semantic Similarity1 Semantic Similarity Methods in WordNet and Their Application to Information Retrieval on the Web Giannis Varelas Epimenidis Voutsakis Paraskevi Raftopoulou Euripides G.M. Petrakis Evangelos Milios

2/10/2016Semantic Similarity2  Semantic Similarity relates to computing the conceptual similarity between terms which are not lexicographically similar “car” “automobile”  Map two terms to an ontology and compute their relationship in that ontology

2/10/2016Semantic Similarity3 Objectives  We investigate several Semantic Similarity Methods and we evaluate their performance  We propose the Semantic Similarity Retrieval Model (SSRM) for computing similarity between documents containing semantically similar but not necessarily lexicographically similar terms

2/10/2016Semantic Similarity4 Ontologies  Tools of information representation on a subject  Hierarchical categorization of terms from general to most specific terms object  artifact  construction  stadium  Domain Ontologies representing knowledge of a domain e.g., MeSH medical ontology  General Ontologies representing common sense knowledge about the world e.g., WordNet

2/10/2016Semantic Similarity5 WordNet  A vocabulary and a thesaurus offering a hierarchical categorization of natural language terms  More than 100,000 terms  An ontology of natural language terms  Nouns, verbs, adjectives and adverbs are grouped into synonym sets (synsets)  Synsets represent terms or concepts stadium, bowl, arena, sports stadium – (a large structure for open-air sports or entertainments)

2/10/2016Semantic Similarity6 WordNet Hierarchies  The synsets are also organized into senses  Senses: Different meanings of the same term  The synsets are related to other synsets higher or lower in the hierarchy by different types of relationships e.g. Hyponym/Hypernym (Is-A relationships) Meronym/Holonym (Part-Of relationships)  Nine noun and several verb Is-A hierarchies

2/10/2016Semantic Similarity7 A Fragment of the WordNet Is-A Hierarchy

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2/10/2016Semantic Similarity9 Semantic Similarity Methods  Map terms to an ontology and compute their relationship in that ontology  Four main categories of methods: Edge counting: path length between terms Information content: as a function of their probability of occurrence in corpus Feature based: similarity between their properties (e.g., definitions) or based on their relationships to other similar terms Hybrid: combine the above ideas

2/10/2016Semantic Similarity10 Example  Edge counting distance between “conveyance” and “ceramic” is 2  An information content method, would associate the two terms with their common subsumer and with their probabilities of occurrence in a corpus

2/10/2016Semantic Similarity11 Semantic Similarity on WordNet  The most popular methods are evaluated  All methods applied on a set of 38 term pairs  Their similarity values are correlated with scores obtained by humans  The higher the correlation of a method the better the method is

2/10/2016Semantic Similarity12 Evaluation MethodTypeCorrelation Rada 1989Edge Counting0.59 Wu 1994Edge Counting0.74 Li 2003Edge Counting0.82 Leackok 1998Edge Counting0.82 Richardson 1994Edge Counting0.63 Resnik 1999Info. Content0.79 Lin 1993Info. Content0.82 Lord 2003Info. Content0.79 Jiang 1998Info. Content0.83 Tversky 1977Feature Based0.73 Rodriguez 2003Hybrid0.71

2/10/2016Semantic Similarity13 Observations  Edge counting/Info. Content methods work by exploiting structure information  Good methods take the position of the terms into account  Higher similarity for terms which are close together but lower in the hierarchy e.g., [Li et.al. 2003]  Information Content is measured on WordNet rather than on corpus [Seco2002]  Similarity only for nouns and verbs  No taxonomic structure for other p.o.s

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2/10/2016Semantic Similarity15 Semantic Similarity Retrieval Model (SSRM)  Classic retrieval models retrieve documents with the same query terms  SSRM will retrieve documents which also contain semantically similar terms  Queries and documents are initially assigned tf x idf weights  q=(q 1,q 2,…q N ), d=(d 1,d 2,…d N )

2/10/2016Semantic Similarity16 SSRM I.Query term re- weighting similar terms reinforce each other I.Query term expansion with synonyms and similar terms II.Document similarity

2/10/2016Semantic Similarity17 Query Term Expansion

2/10/2016Semantic Similarity18 Observations  Specification of T ?  Large T may lead to topic drift  Word sense disambiguation for expanding with the correct sense  Expansion with co-concurring terms? SVD, local/global analysis  Semantic similarity between terms of different parts of speech?  Work with compound terms (phrases)

2/10/2016Semantic Similarity19 Evaluation of SSRM  SSRM is evaluated through intellisearch a system for information retrieval on the WWW intellisearch  1,5 Million Web pages with images  Images are described by surrounding text  The problem of image retrieval is transformed into a problem of text retrieval

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2/10/2016Semantic Similarity21 Methods  Vector Space Model (VSM)  SSRM  Each method is represented by a precision/recall plot  Each point is the average precision/recall over 20 queries  20 queries from the list of the most frequent Google image queries

2/10/2016Semantic Similarity22 Experimental Results

2/10/2016Semantic Similarity23 MeSH and MedLine  MeSH: ontology for medical and biological terms by the N.L.M. 22,000 terms  MedLine: the premier bibliographic medical database of N.L.M. 13 Million references

2/10/2016Semantic Similarity24 Evaluation on MedLine

2/10/2016Semantic Similarity25 Conclusions  Semantic similarity methods approximated the human notion of similarity reaching correlation up to 83%  SSRM exploits this information for improving the performance of retrieval  SSRM can work with any semantic similarity method and any ontology

2/10/2016Semantic Similarity26 Future Work  Experimentation with more data sets (TREC) and ontologies  Extend SSRM to work with Compound terms More parts of speech (e.g., adverbs) Co-occurring terms More terms relationships in WordNet More elaborate methods for specification of thresholds

2/10/2016Semantic Similarity27 Try our system on the Web  Semantic Similarity System:  SRRM: