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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

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 ofwords

A word is a sequence of letters surrounded byseparators

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 maximumallowed distance between them are specified

>e.g,within distance (enhance, retrieval, 4) will matchenhance the power of retrieval


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Definition

A syntax composed of atoms that retrieve documents, and ofBoolean 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 contextqueries

All the documents matching a portion of the userquery are retrieved


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Pattern Matching

Data retrieval

A pattern is a set of syntactic features that mustoccur in a text segment

Types Words

Prefixes

e.q comput->computer,computation,computing,etc

Suffixese.q ters->computers,testers,painters,etc

Substringse.q tal->coastal,talk,metallic,etc

Ranges

between heldand hold->hoaxand hissing


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Allowing errors

Retrieve all text words which all similarto the

given word

edit distance:

the minimum number of character insertions,deletions, and replacements needed to maketwo strings equal, e.q , flowerand flo wer

maximum allowed edit distance:

query specifies the maximum number of allowederrors for a word to match the pattern


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Regular expressions

union:if e1and e2are regular expressions , then(e1|e2)matches what e1or e2matches

concatenation:if e1and e2are regular expressions, the

occurrences of (e1e2) are formed by the occurrences of e1immediately followed by those of e2

repetition:if e is a regular expression , then (e*)matches a sequence of zero or more contiguousoccurrence of e

pro(blem|tein)(s|)(0|1|2)*->problem2andproteins


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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 theSubject field


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A hypertext is a directed graphwhere nodes hold sometext (text contents)

the linksrepresent connections between nodes orbetween positions inside nodes (structural connectivity)

Hypertext


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Hypertext : WebGlimpse

WebGlimpse: combine browsing and searching onthe Web


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Hierarchical Structure


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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 InformationRetrieval Application Service Definition

Can be implemented on any platform

Query bibliographical information using astandard interface between the client and thehost 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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Overlapped Lists

The model allow for the areas of a region tooverlap, 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 onlysections, or only paragraphs.

A reference is a pointer to a region of thedatabase.


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Tree Matching

The leaves of the query can be not onlystructural elements but also text patterns,meaning that the ancestor of the leaf must

contain that pattern.

Documents

Chapter 4 Ql