XML? Database

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XML? Database

• ???
• ???????

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• Database, Web, and XML
• XML Database Systems
• Data Models
• Query Language and Processing
• Storage and Index
• Other issues

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Database and Web, before XML

• DB a back-end server for Web Applications
• CGI
• JDBC
• Embedded SQL
• Web
• Information Retrieval
• Target to manage (Web DB)

Scripts
ThinClient
HTML
MiddleTier
Web Server
Template Engine
HTMLTemplates
Scripts
Application Server
ApplicationCode
MappingCode
BackEnd
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XML

• eXtensible Markup Language
• A new emerging standard for data representation
  and exchange on the internet
• See the XML catalog , http//www.xml.org
• Separating content from presentation
• Easy to provide multiple view of the same data
• Easily parsed and self-describing

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XML

• Extensible a dynamic data model
• Simple human-readable, easy to use
• Flexible for handling complex data
• Portable for cross-platform data exchange
• Standard easy to integrate, widely adopted

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HTML? XML ?? ??
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XML Is All About Data

• HTML example
• ltheading1gt Invoice lt/heading1gt
• ltboldgtTo Joe Bloggs ltPgt
• From J. Abrams ltPgt
• Date 2/1/1999ltPgt
• Amount 100 ltPgt
• Tax 21 ltPgt
• Total 121 lt/boldgt

Datamixed withpresentation
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XML Is All About Data
HumanReadable

• XML example
• ltInvoicegt
• ltCustomergt Joe Bloggs lt/Customergt
• ltFromgt J. Abrams lt/Fromgt
• ltDate year1999 month2 day 1 /gt
• ltAmount unit Dollarsgt 100 lt/Amountgt
• ltTaxRategt 21 lt/TaxRategt
• ltTotal currency Dollarsgt121 lt/Totalgt
• lt/Invoicegt

Comeswith Tags
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XML Is All About Data
Extensible

• XML example
• ltInvoicegt
• ltCustomergt
• ltNamegtJoe Bloggs lt/Namegt
• ltAddressgt 25 Mall Road lt/Addressgt
• lt/Customergt
• ltFromgt J. Abrams lt/Fromgt
• ltDate year1999 month2 day 1 /gt
• ltAmount unit Dollarsgt 100 lt/Amountgt
• ltTaxRategt 21 lt/TaxRategt
• ltTotal unit Dollarsgt121 lt/Totalgt
• lt/Invoicegt

ltNamegtJoe Bloggs lt/Namegt ltAddressgt 25 Mall
Road lt/Addressgt
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XML Family of Standards

• XML
• DOM (Document Object Model)
• XML Namespaces
• XSL (style language)
• XQL (XSL query language)
• XML Data / DCD / Schema
• XUL (updates, future)
• many more

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Building Web Applications with XML
Scripts
ThinClient

• Quickly react to changes
• Lower maintenance costs
• Does not depend on a single vendor

HTML
MiddleTier
Web Server / App Server
ApplicationCode DOM
XSL
XML Server
Standard API andTemplate Language
XML
BackEnd
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Legacy DBs for XML Applications

• XML as a new data-exchange format
• for legacy DB applications
• DB2XML
• Transforming the results of database queries or
  complete databases into XML documents or into
  HTML documents using XSLT stylesheets.
• DB2XML can be used
• as a standalone tool (with GUI or command line),
• as a servlet to dynamically generate
  XML-documents
• using the DB2XML API

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XML Database Systems

• 3 approaches
• Build special-purpose systems
• Lore, Strudel
• Best performance for XML data
• Use object-oriented database systems
• eXelon, Monet, Ozone
• Object-oriented modeling
• Use relational database systems
• Oracle, Microsoft
• Matured large market

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Lore
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eXelon
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Oracle 8i
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Data Models for XML

• XML is not a data model
• Structure of an XML document
• an ordered list of elements
• each element
• may have a set of attributes
• may have (sub)elements (nested elements)
• Structured data and full text mixed together
• DOM defines how to translate an XML document into
  a data structure for processing
• Need a true data model for XML data

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OEM a Semi-structured Data Model

• Object Exchange Model (Lore)
• Semi-structured Data
• Self-describing structure, the lack of schema
• the structure changes rapidly and unpredictably
• Labeled direct graph
• Node Object (OID) or atomic value (leaf)
• Labeled Edge object-subobject relationship

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OEM, an example

• ltDBGroupgt
• ltMember Name? Advisorm1gt
• ltAgegt28lt/Agegt
• lt/Membergt
• ltMember IDm1, Projectp1gt
• ltNamegt?lt/Namegt
• ltAdvisorgt?lt/Advisorgt
• lt/Membergt
• ltProject IDp1 Memberm1gt
• ltTitlegtXML DBlt/Titlegt
• lt/Projectgt
• lt/DBGroupgt

DBGroup
1
Member
Project
Member
4
3
2
IDm1, Projectp1
NameSmith, Advisorm1
IDp1, Projectm1
Age
Name
Title
Advisor
5
7
6
8
Text
Text
Text
Text
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9
10
11
28
?
?
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Issues in Data Modeling

• How to simultaneously view XML information in
  both
• a set of documents
• a single large database
• No loss of information in XML
• How to represent the Ordering of elements
• external/internal entities, processing
  instructions

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• XML DB Design
• When should attributes (subelements) be used?
• Is a 1-to-1 relationship best represented using
  element nesting or IDREFs?
• How to translate the conceptual model (OEM?) into
  an XML encoding?
• Need to identify the relationship between DTDs
  and traditional DB schema

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Query Languages for XML DB

• Requirements
• Path Expressions
• Queries over
• the structured and semistructured data
• full text
• the mixture of data elements and full text
• W3C, Query Languages for the Web, 1998
• QL for semistructured data
• Lorel, UnQL
• XQL, XML-QL

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XML-QL

• Syntax
• Select ltvariable-listgt where ltXML-patterngt
• Example
• select n, h
• where ltpersongt ltageagt
• ltnamegt n lt/namegt
• ltaddressgt ?? ??? ???3?lt/addressgt
• lthobbygt h lt/hobbygt
• lt/persongt, a gt 18

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Issues in Query Processing

• The true requirements for XML QL is not known
• Need to review all facets of traditional query
  processing
• Need to Develop a new IR model
• proximity in XML documents
• similarity measure between XML elements

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• How to integrate
• traditional (DB) query processing model and
• information retrieval model
• Optimization Schemes
• for not well-structured XML data
• for queries mixed with full text retrieval and
  structured/semistructured search

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Storage Structure and Indexing

• Clustering schemes for storing XML data
• New index types
• for quickly finding certain elements, attributes,
  and more complex structural patterns
• element orderings
• Determine the level of parsing for storing XML
  documents
• Based on the analysis of encoding pattern
• merging identical text strings (sub-patterns) by
  using appropriate IDREFs
• compression based on regular patterns

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Issues in Various DB Features

• Full view support for XML
• both virtual and materialized views
• incremental maintenance
• XSL as a view definition language
• Data integrity issue
• What are constraints on XML data?
• key, referential, domain
• How to represent the constraints
• How to check them when changes occur

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• Trigger
• active database capabilities in XML
• Transaction Control over XML database
• Performance Evaluation
• need to make an appropriate benchmark for XML
  data
• XML data set
• query types
• mix of queries and updates

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References

• Research issues
• Data Management for XML Research Directions,
  http//www-db.stanford.edu/wisom/xml-whitepaper.h
  tml
• More on Data Management for XML,
  http//www.cs.washington.edu/homes/alon/widom-resp
  onse.html
• Storing XML data into RDBMSs
• A Performance Evaluation of Alternative Mapping
  Schemes for Storing XML Data in a Relational
  Database, ercim.inria. publications/RR-3680
• XML Database Systems
• http//www.xmlsoftware.com/database/