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Modern Information Retrieval

In Chapter 4 of Modern Information Retrieval, we explore various query languages pivotal for effective information retrieval. The user’s query type is influenced by the underlying retrieval model. This chapter covers keyword-based queries, including single-word queries, context queries, phrase queries, and proximity queries. It also delves into Boolean queries and pattern matching techniques such as edit distance and regular expressions. These elements enhance the retrieval process, ensuring more relevant search results tailored to user needs.

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Modern Information Retrieval

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Presentation Transcript

  1. Modern Information Retrieval Chapter 4 Query Languages

  2. The type of query the user might formulate is largely dependent on the underlying information retrieval model

  3. Keyword-based querying • single-word queries • text documents are long sequences of words • ranking of results by term frequency and inverse document frequency • exact positions where the query word appears may need to be output

  4. context queries • to search words near other words • phrase query: a sequence of single-words • enhance retrieval • proximity query: a sequence of single-words with a maximum allowed distance between them • enhance the power of retrieval • the words may or may not be required to appear in the same order as in the query

  5. Boolean queries • e1 BUT e2

  6. Pattern matching • types of patterns • word: computer • prefix of a word: comput • suffix of a word: ter • substring of a word: ute • range formed by two words in lexicographical order: communication and computer

  7. word with an error threshold • edit distance: minimum number of character insertions, deletions, and replacements needed to make the query and the target equal • Computeers • Unit cost edit distance • W(ab)=1, ab (Replacement) • W(a  )=W(b)=1 (Deletion and Insertion)

  8. Given any two strings S1=abac, S2=aaccb • Evaluated by dynamic programming method • The edit distance is 3 a b a c c b (1 deletion, 2 insertions) a a c c b

  9. regular expression • a regular expression is a pattern built up by simple strings and the union, concatenation and repetition operators • pro(blem︱tein)(s︱ε)(0︱1︱2)*

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