XML and Databases

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XML and Databases
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Data and Document

• There are really at least two distinct XML uses
• XML to describe Documents
• XML to describe Data

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Document vs Data
XML for documents describes complex document
structures many elements with mixed content data
types usually just text
Data XML, simpler describing data structure, No
or little mixed content data types varied and
important
Machine to machine communication
Document processing
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XML Data

• Xml for data is usually simplermore straight
  forward in structure less hierarchical levels,
  no, or very few mixed elements
• It is meant to be generated and read by
  applications
• Data types are more importantthus the use of
  schemas rather than DTDs

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Reasons for XML

• Explosion in the need to share data over the
  Internet from enterprise databases
• Different database softwares, application
  softwares, incompatible data schemas
• XML provides an easily managed format for
  universal communication

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Universal Communication
Unicode Multilanguage support
Application and platform independent data format
Data logic separate from presentation logic
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Importance to Database

• David Kroenke lists these ways in which XML is
  important for databases
• Standard means for representing domains
• Standard means for expressing database views
• Clean separation of structure, content and
  materialization
• Facility for document validity checking
• Industry standards for document types
• Kroenke, David Database Processing, Eighth
  Edition Prentice Hall, NJ, 2001, p 432

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Issues

• XML does not always translate well to relational
  data models
• XML has a primarily hierarchical structure
• Some sort of Data Mapping must occur

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Data Mapping
XML application
Database server SQL
Mapping to XML
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Approaches to Data Mapping

• Result set mappingmaps the XML to the result set
  of an SQL Query. (A row element is created for
  each record. Each column becomes an element or
  attribute)
• Schema mappingthe database structure is
  generated to and from XML Schema (we will cover
  this more later)

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Commercial Database Support

• SQL Servercan generate XML from SQL and can
  update tables from XML files.
• Oracle 9-I includes XSU (XML SQL Utility that
  will
• Generate XML based on SQL queries
• Extract data from XML for insert or update

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XML Databases

• There has been some talk of creating XML
  databasesthat is a database whose native format
  is XML and which processes queries with XPath and
  XQuery
• There has also been some movement to include XML
  as a native Data type in Relational databases

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The Gist

• XML is best used to communicate data
• Databases are best used to store data