Chapter 4 : Query Languages

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Chapter 4 Query Languages

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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,e.g,near
  other words
• 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
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Boolean Queries

• Operands
• -(e1 OR e2)
• select all documents which satisfy e1 or e2
• -(e1 AND e2)
• select all documents which satisfy both e1 and
  e2
• -(e1 BUT e2)
• select all documents which satisfy e1 but not
  e2
• 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

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Pattern Matching

• A pattern is a set of syntactic features that
  must occur in a text segment
• Types
• -words
• -prefixes
• e.q comput-gtcomputer ,computation,com
  puting,etc
• -suffixes
• e.q ters-gtcomputers,testers,painters
  ,etc
• -substrings
• e.q tal-gtcoastal,talk,metallic,etc
• -Ranges
• between held and hold-gthoax and
  hissing

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Pattern Matching

• 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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Pattern Matching

• 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
• -contentswords,phrases,or patterns
• -structural constraintscontainment,proximity,o
  r 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
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Hierarchical Structure
Recursive decomposition of the text
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Hierarchical Structure
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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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PAT Expressions

• What is PAT tree?
• The areas of a region cannot nest or overlap

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PAT Tree
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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.

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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
Model
Queries allowed
word,set operations words words words
Boolean Vector Probabilistic BBN
Relationship between types of queries and models
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Boolean Model

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Vector Model

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Probabilistic Model

• Probabilistic Model
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Bayesian Belief Network

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Bayesian Belief Network

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Trends and Research Issues
The types of queries covered and how they are
structured