Query Languages: Patterns

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Query LanguagesPatterns Structures
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Pattern Matching

• Pattern
• a set of syntactic features that must occur in a
  text segment
• Types of patterns
• Words string (sequence of characters) in the
  text
• Prefixes string forming the beginning of a text
  word (e.g., comput ? computer, computation)
• Suffixes string forming the termination of a
  text word (e.g., ters ? computers, painters)
• Substrings string appeared within a text word
  (allowed word separators) (e.g., tal ? talk,
  metallic any flow ? many flowers)

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Pattern Matching (cont.)

• More Types of Patterns
• Ranges a pair of strings matched any word lying
  between them in lexicographical order
• (e.g., held to hold ? hoax, hissing)
• Allowing errors retrieving word similar to given
  word
• (e.g., flower ? flo wer edit distance 1)
• Regular expressions general patterns built up by
  simple strings and operators
• (e.g., pro (blem tein) (s e) (0 1 2) )
• ? Problem02, proteins
• Extended patterns classes of characters,
  conditional expressions, wild characters,
  combinations

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Structural Queries

• Structural query
• mixing contents and structure in queries
• content constraints (words, phrases, patterns)
• structural constraints (containment, proximity)
  and restrictions on structural elements
  (chapters, sections)
• Type of structures of text
• form-like fixed structure
• hypertext structure
• hierarchical structure

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Structural Queries (cont.)

• Types of structures

form
hypertext
hierarchical
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Fixed Structure

• Traditional restrictions
• documents had a fixed set of fields
• each field had some text inside
• only rarely the fields appear in any order or
  repeat
• fields were not allowed to nest or overlap
• retrieval specifying a given basic pattern to be
  found only in a given field
• Characteristics
• reasonable to retrieve text collection having a
  fixed structure (e.g. mail archive) ? inadequate
  to represent the hierarchical structure such as
  HTML docs
• expansion to relational DB model

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Hypertext

• Hypertext (navigational)
• a directed graph where the nodes hold some text
  and the links represent connections between nodes
  or between positions inside the nodes
• Browsing / Searching in hypertext
• retrieval from a hypertext browsing (traversing
  the hypertext nodes following link ? navigational
  activity)
• even in web, one can search by the text contents
  of the nodes, but not by their structural
  connectivity
• some search engines now allow searching for
  specific source or destination anchors (but not
  general structure content queries)

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Hierarchical Structure

• Hierarchical structure
• an intermediate structuring model lying between
  fixed structure and hypertext
• represents a recursive decomposition of the text
• a natural model for many text collections, e.g.,
  books, articles, legal documents, structured
  programs, etc.
• Hierarchical models
• PAT Expressions, Overlapped Lists, List of
  References, Proximal Nodes, Tree Matching
• Issues in hierarchical models
• static or dynamic structure, restrictions on the
  structure, integration with text, query language

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Query Protocols

• Query protocols
• query language used to query text database
• standards intended not for human use but for
  querying library systems and querying CD-ROMs
• Some important query protocols
• Z39.50
• WAIS
• CCL
• CD-RDx
• SFQL