Chapter 4 : Query Languages

1
Chapter 4 Query Languages

• Baeza-Yates, 1999
• Modern 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 need
• Keyword-based queries are popular
• 1. Single-Word Queries
• 2. Context Queries
• 3. Boolean Queries
• 4. Natural Language

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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
• gta sequence of single-word queries
• gte.g, enhance retrieval
• Proximity
• gta sequence of single words or phrases, and a
  maximum allowed distance between them are
  specified
• gte.g,within distance (enhance, retrieval, 4)
  will match enhance the power of
  retrieval

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Boolean Queries

• 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)

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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

8
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-gtcomputer ,computation,comput
  ing,etc
• Suffixes
• e.q ters-gtcomputers,testers,painters,et
  c
• Substrings
• e.q tal-gtcoastal,talk,metallic,etc
• Ranges
• between held and hold-gthoax 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(e1e2) 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(blemtein)(s?)(012)-gtproblem2 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

• Documenta 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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Hypertext

• 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)

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Hypertext WebGlimpse
WebGlimpse combine browsing and searching on the
Web
15
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 Server
Repository Digital library
Z39.50 Client
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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
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.