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eXtensible Markup Language (XML)

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eXtensible Markup Language (XML) By: Albert Beng Kiat Tan Ayzer Mungan Edwin Hendriadi Outline of Presentation Introduction Comparison between XML and HTML XML Syntax ... – PowerPoint PPT presentation

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Title: eXtensible Markup Language (XML)


1
eXtensible Markup Language (XML)
  • By
  • Albert Beng Kiat Tan
  • Ayzer Mungan
  • Edwin Hendriadi

2
Outline of Presentation
  • Introduction
  • Comparison between XML and HTML
  • XML Syntax
  • XML Queries and Mediators
  • Challenges
  • Summary

3
What is XML?
  • eXtensible Markup Language
  • Markup language for documents containing
    structured information
  • Defined by four specifications
  • XML, the Extensible Markup Language
  • XLL, the Extensible Linking Language
  • XSL, the Extensible Style Language
  • XUA, the XML User Agent

4
XML.
  • Based on Standard Generalized Markup Language
    (SGML)
  • Version 1.0 introduced by World Wide Web
    Consortium (W3C) in 1998
  • Bridge for data exchange on
  • the Web

5
Comparisons
XML
HTML
  • Extensible set of tags
  • Content orientated
  • Standard Data infrastructure
  • Allows multiple output forms
  • Fixed set of tags
  • Presentation oriented
  • No data validation capabilities
  • Single presentation

6
Authoring XML Elements
  • An XML element is made up of a start tag, an end
    tag, and data in between.
  • Example
  • ltdirectorgt Matthew Dunn lt/directorgt
  • Example of another element with the same value
  • ltactorgt Matthew Dunn lt/actorgt
  • XML tags are case-sensitive
  • ltCITYgt ltCitygt ltcitygt
  • XML can abbreviate empty elements, for example
  • ltmarriedgt lt/marriedgt can be abbreviated to
  • ltmarried/gt

7
Authoring XML Elements (contd)
  • An attribute is a name-value pair separated by an
    equal sign ().
  • Example
  • ltCity ZIP94608gt Emeryville lt/Citygt
  • Attributes are used to attach additional,
    secondary information to an element.

8
Authoring XML Documents
  • A basic XML document is an XML element that can,
    but might not, include nested XML elements.
  • Example
  • ltbooksgt
  • ltbook isbn123gt
  • lttitlegt Second Chance lt/titlegt
  • ltauthorgt Matthew Dunn lt/authorgt
  • lt/bookgt
  • lt/booksgt

9
XML Data Model Example
  • ltBOOKSgt
  • ltbook id123 loclibrarygt
  • ltauthorgtHulllt/authorgt
  • lttitlegtCalifornialt/titlegt
  • ltyeargt 1995 lt/yeargt
  • lt/bookgt
  • ltarticle id555 ref123gt
  • ltauthorgtSult/authorgt
  • lttitlegt Purduelt/titlegt
  • lt/articlegt
  • lt/BOOKSgt

Hull
10
Authoring XML Documents (contd)
  • Authoring guidelines
  • All elements must have an end tag.
  • All elements must be cleanly nested (overlapping
    elements are not allowed).
  • All attribute values must be enclosed in
    quotation marks.
  • Each document must have a unique first element,
    the root node.

11
Authoring XML Data Islands
  • A data island is an XML document that exists
    within an HTML page.
  • The ltXMLgt element marks the beginning of the data
    island, and its ID attribute provides a name that
    you can use to reference the data island.

12
Authoring XML Data Islands (contd)
  • Example
  • ltXML IDXMLIDgt
  • ltcustomergt
  • ltnamegt Mark Hanson lt/namegt
  • ltcustIDgt 29085 lt/custIDgt
  • lt/customergt
  • lt/XMLgt

13
Document Type Definitions (DTD)
  • An XML document may have an optional DTD.
  • DTD serves as grammar for the underlying XML
    document, and it is part of XML language.
  • DTDs are somewhat unsatisfactory, but no
    consensus exists so far beyond the basic DTDs.
  • DTD has the form
  • lt!DOCTYPE name markupdeclarationgt

14
DTD (contd)
  • Consider an XML document
  • ltdbgtltpersongtltnamegtAlanlt/namegt
  • ltagegt42lt/agegt
  • ltemailgtagb_at_usa.net
    lt/emailgt
  • lt/persongt
  • ltpersongtlt/persongt
  • .
  • lt/dbgt

15
DTD (contd)
  • DTD for it might be
  • lt!DOCTYPE db
  • lt!ELEMENT db (person)gt
  • lt!ELEMENT person (name, age, email)gt
  • lt!ELEMENT name (PCDATA)gt
  • lt!ELEMENT age (PCDATA)gt
  • lt!ELEMENT email (PCDATA)gt
  • gt

16
DTD (contd)
  • Occurrence Indicator

Indicator Occurrence Occurrence
(no indicator) Required One and only one
? Optional None or one
Optional, repeatable None, one, or more
Required, repeatable One or more
17
XML Query Languages
  • The first XML query languages
  • LOREL (Stanford)
  • XQL
  • Several other query languages have been developed
    (e.g. UNQL, XPath)
  • XML-QL considered by W3C for standardization
  • Currently W3C is considering and working on a
    new query language XQuery

18
A Query Language for XML XML-QL
  • Developed at ATT labs
  • To extract data from the input XML data
  • Has variables to which data is bound and
    templates which show how the output XML data is
    to be constructed
  • Uses the XML syntax
  • Based on a where/construct syntax
  • Where combines from and where parts of SQL
  • Construct corresponds to SQLs select

19
XML-QL Query Example 1
  • Retrieve all authors of books published by Morgan
    Kaufmann
  • where ltbookgt
  • ltpublishergtltnamegt
  • Morgan Kaufmann
  • lt/namegt lt/publishergt
  • lttitlegt T lt/titlegt
  • ltauthorgt A lt/authorgt
  • lt/bookgt in www.a.b.c/bib.xml
  • construct ltresultgt A lt/resultgt

20
XML-QL Query Example 2
  • XML-QL query asking for all bookstores that sell
    The Java Programming Language for under 25
  • where ltstoregt
  • ltnamegt N lt/namegt
  • ltbookgt
  • lttitlegt The Java Programming Language
    lt/titlegt
  • ltpricegt P lt/pricegt
  • lt/bookgt
  • lt/storegt in www.store/bib.xml
  • P lt 25
  • construct ltresultgt N lt/resultgt

21
Semistructured Data and Mediators
  • Semistructured data is often encountered in data
    exchange and integration
  • At the sources the data may be structured (e.g.
    from relational databases)
  • We model the data as semistructured to facilitate
    exchange and integration
  • Users see an integrated semistructured view that
    they can query
  • Queries are eventually reformulated into queries
    over the structured resources (e.g. SQL)
  • Only results need to be materialized

22
What is a mediator ?
  • A complex software component that integrates and
    transforms data from one or several sources using
    a declarative specification
  • Two main contexts
  • Data conversion converts data between two
    different models
  • e.g. by translating data from a relational
    database into XML
  • Data integration integrates data from different
    sources into a common view

23
Converting Relational Database to XML
  • Example Export the following data into XML and
    group books by store
  • Relational Database
  • Store (sid, name, phone)
  • Book (bid, title, authors)
  • StoreBook (sid , bid, price, stock)

24
Converting Relational Database to XML (Contd)
  • XML
  • ltstoregt ltnamegt lt/namegt
  • ltphonegt lt/phonegt
  • ltbookgt lttitlegt lt/titlegt
  • ltauthorsgt lt/authorsgt
  • ltpricegt lt/pricegt
  • lt/bookgt
  • ltbookgtlt/bookgt
  • lt/storegt

25
Challenges facing XML
  • Integration of data sharing
  • Security
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