Chapter 4 : Query Languages
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Transcript of Chapter 4 : Query Languages
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Chapter 4 : Query Languages
Baeza-Yates, 1999Modern Information Retrieval
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Outline
Keyword-Based Querying Patten Matching Structural Queries Query Protocols Trends and Research Issues
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Keyword-Based Querying
A query is formulation of a user information needKeyword-based queries are popular
1. Single-Word Queries2. Context Queries3. Boolean Queries4. Natural Language
Data Retrieval
Information Retrieval
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Single-Word Queries
A query is formulated by a word A document is formulated by long sequences of
words A word is a sequence of letters surrounded by
separators What are letters and separators? e.g,’on-line’
The division of the text into words is not arbitrary
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Context Queries
Definition - Search words in a given context Types
Phrase >a sequence of single-word queries >e.g, enhance retrieval Proximity >a sequence of single words or phrases, and a maximum
allowed distance between them are specified >e.g,within distance (enhance, retrieval, 4) will match
‘…enhance the power of retrieval…’
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Definition A syntax composed of atoms that retrieve documents,
and of Boolean operators which work on their operands
e.g, translation AND syntax OR syntactic
Fuzzy Boolean Retrieve documents appearing in some operands (The AND
may require it to appear in more operands than the OR)
Boolean Queries
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Natural Language
Generalization of “fuzzy Boolean” A query is an enumeration of words and context
queries All the documents matching a portion of the user
query are retrieved
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Pattern Matching Data retrieval A pattern is a set of syntactic features that must
occur in a text segment Types
Words Prefixes e.q ‘comput’->’computer’ ,’computation’,’computing’,etc Suffixes e.q ‘ters’->’computers’,’testers’,’painters’,etc Substrings e.q ‘tal’->’coastal’,’talk’,’metallic’,etc Ranges between ‘held’ and ‘hold’->’hoax’ and ‘hissing’
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Allowing errors
Retrieve all text words which all ‘similar’ to the given word
edit distance: the minimum number of character insertions,
deletions, and replacements needed to make two strings equal, e.q , ‘flower’ and ‘flo wer’
maximum allowed edit distance: query specifies the maximum number of allowed
errors for a word to match the pattern
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Regular expressions
union: if e1 and e2 are regular expressions , then(e1|e2) matches what e1 or e2 matches
concatenation: if e1 and e2 are regular expressions, the occurrences of (e1e2) are formed by the occurrences of e1 immediately followed by those of e2
repetition: if e is a regular expression , then (e*) matches a sequence of zero or more contiguous occurrence of e
‘pro(blem|tein)(s|є)(0|1|2)*’->’problem2’ and ‘proteins’
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Structural Queries
Mixing contents and structure in queries - contents: words, phrases, or patterns - structural constraints: containment, proximity,
or other restrictions on structural elements Three main structures - Fixed structure - Hypertext structure - Hierarchical structure
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Fixed Structure
Document:a fixed set of fields
EX: a mail has a sender, a receiver, a date, a subject and a body field
Search for the mails sent to a given person with “football” in the Subject field
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A hypertext is a directed graph where nodes hold some text (text contents)
the links represent connections between nodes or between positions inside nodes (structural connectivity)
Hypertext
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Hypertext : WebGlimpse
WebGlimpse: combine browsing and searching on the Web
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Hierarchical Structure
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Hierarchical Structure
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Hierarchical Structure
PAT Expressions Overlapped Lists Lists of References Proximal Nodes Tree Matching
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Query Protocols
Z39.50 WAIS (Wide Area Information Service)
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Z39.50
American National Standard Information Retrieval Application Service Definition
Can be implemented on any platform Query bibliographical information using a
standard interface between the client and the host database manager
Z39.50 protocol is part of WAIS
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Z39.50 Brief history
Z39.50-1988(version 1) Z39.50-1992(version 2) Z39.50-1995(version 3) Version 4, development began in Autumn 1995
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Using Z39.50 over the WWW
WWW Client WWW Z39.50
Z39.50 Client
Z39.50Server
RepositoryDigital library
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WAIS (Wide Area Information Service)
Beginning in the 1990s Query databases through the Internet
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Trends and Research Issues
Model Queries allowed
BooleanVectorProbabilisticBBN
word,set operationswordswordswords
Relationship between types of queries and models
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Query Language Taxonomy
The types of queries covered and how they are structured
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PAT Tree Expression
The model allow for the areas of a region to overlap or nest
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Overlapped Lists
The model allow for the areas of a region to overlap, but not to nest
It is not clear, whether overlapping is good or not for capturing the structural properties
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Lists of References
Overlap and nest are not allowed All elements must be of the same type,e.g only
sections, or only paragraphs. A reference is a pointer to a region of the
database.
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Proximal Nodes
This model tries to find a good compromise between expressiveness and efficiency.
It does not define a specific language, but a model in which it is shown that a number of useful operators can be included achieving good efficiency.
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Tree Matching
The leaves of the query can be not only structural elements but also text patterns, meaning that the ancestor of the leaf must contain that pattern.