Semantic search

LOW RECALL

• ENHANCEMENTS:
• Stemming
• Eg: Moving, moved, moves → move
• Word Similarity
• Eg: Clothes ~ Apparel
• SRS Augmentation
• ~

• QUERY EXPANSION

• QUERY EXPANSION

• Query expansion is the process of reformulating a seed query to improve retrieval performance.
• Techniques involved:
• Finding synonyms of words.
• Finding all the various morphological forms of a word by stemming

• TYPES OF QUERY EXPANSION

• GLOBAL : Examine word occurrences and relationships using thesaurus. It can be constructed manually or automatically.
• LOCAL: Using the top ranked documents retrieved by the original query.

• GLOBAL QUERY EXPANSION

• Manual Thesaurus Generation:
• Use of a controlled vocabulary (maintained by human editors) that is built up from sets of synonymous names for concepts.
• Automatic Thesaurus Generation:
• Exploit word co occurrence.
• Exploit grammatical relations or grammatical dependencies.

• ANALYSIS OF QUERY EXPANSION

• Query expansion is effective in increasing recall of relevant documents.
• But it may significantly decrease precision, particularly when the query contains ambiguous terms.
• In general a domain specific thesaurus is required for better performance.

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