Introduction To XML

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Introduction To XML

• By Abdul Habra
• October 30, 2002

www.tek271.com/articles/articles.html
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Topics

• Expectations
• What is XML
• Acronyms
• History
• Motivation
• Where/Who uses XML
• When to use/not use
• Technologies
• Whats next
• Feedback

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Expectations

• Understand what XML is, even if you are not a
  programmer
• Tell you what are some of the acronyms and
  technologies
• What to do to learn more
• Will NOT learn API or programming

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What Is XML

• Data formatted in a way that is easy for humans
  and machines to read
• eXtensible Markup Language
• Text data, i.e. not binary
• When stored in a file, one can view it with
  Notepad
• Not a proprietary language
• Fast becoming a universal data translation
  language

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Example
lt?xml version"1.0"?gt ltCustomerListgt
ltcustomer id"1"gt ltfnamegt Jen lt/fnamegt
ltlnamegt Lo lt/lnamegt lttitlegt CEO lt/titlegt
ltcompanygt Blue Moon Enterprises lt/companygt
lt/customergt ltcustomer id"2"gt ltfnamegt
Austin lt/fnamegt ltlnamegt Powers lt/lnamegt
lttitlegt Gold Member lt/titlegt ltcompanygt
MiniEvil lt/companygt lt/customergt lt/CustomerListgt
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Acronyms

• DOM, SAX, DTD, XSL, XSLT, SOAP, UDDI,
• X eXtensible
• D Document
• L Language
• O Object
• P Protocol
• See
• www.tek271.com/articles/acroStats/AcroStat.html

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XMLs History

• Derived from SGML (Standard Generalized Markup
  Language), that started in the 1960s
• Specs published in Feb 1998
• Began to get popular in 2000
• Supported by most vendors and platforms
• MS, IBM, Sun, Borland,
• I.E. gt 5.0 can display XML data

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Motivation

• Businesses needed to communicate over the
  Internet. (B2B)
• Send documents and complex data that have
  different formats
• Word, PDF, Excel, Access, comma separated,
• E.g. think how many ways a persons name can be
  formatted
• Different Internet clients capabilities.
• Desktops with different browsers
• PDAs, Mobile phones,

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Where/Who Uses XML

• In databases to store or move data
• In configuration files
• In communication between systems
• MS .NET, IE, SQL Server,
• IBM donated their Java XML technologies to
  Apache
• Sun Supports XML, Web Services,
• I started using it at RR in 1998

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To Use Or Not To Use

• Use when you want to
• Communicate between different programs and
  systems
• Store complex configuration data
• Display output by different clients, e.g.
  desktops and PDAs. Use XSLT
• Do not use when
• You need a relational database model, XML is less
  efficient than RDBs

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XML Technologies

• The following slides will introduce some XML
  related terms and technologies
• This a high level definition
• Some definitions are approximated for the sake of
  simplicity

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Tags And Elements

• Consider the following XML snippet
• ltcustomer id"2"gt
• ltfnamegt Austin lt/fnamegt
• ltlnamegt Powers lt/lnamegt
• lttitlegt Gold Member lt/titlegt
• ltcompanygt MiniEvil lt/companygt
• lt/customergt
• ltfnamegt is a start tag
• lt/fnamegt is an end tag
• ltfnamegtAustinlt/fnamegt is an element
• id (in customer tag) is an attribute

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Well-Formed/Valid Documents

• Well-Formed document
• Follows XML syntax
• Every start tag must have an end tag
• If a document is not well-formed, then it is NOT
  an XML document
• Valid document
• Must be well-formed
• Must follow a template (DTD) that specifies what
  elements and attributes can/must exist in the
  document

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Documents Templates

• Consider the following XML snippet
• ltcustomer id"2"gt
• ltfnamegt Austin lt/fnamegt
• ltlnamegt Powers lt/lnamegt
• ltcompanygt MiniEvil lt/companygt
• ltbalancegt 1009 lt/balancegt
• lt/customergt
• A template will specify that customer element
• Must have an id attribute that is an integer
• Must contain an fname element that is a string
• Can contain a balance element that is an integer

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DTD And Schema

• A standard was created for defining document
  templates Document Type Definition (DTD)
• DTD has a confusing syntax and is not XML
• In 2001 a new standard was created XML Schema
• XML Schemas are well-formed XML documents
• Schemas provide better control of the data types

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XML Parsers

• To parse is to classify a word or analyze a
  sentence in terms of grammar
• A Parser is a program that reads source code of a
  language and recognizes each element of it
• An XML parser reads the XML source, breaks it
  down into its elements, and allows another
  program to act on these elements

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Processing XML

• To process an XML document, you have several
  options
• Write a program to parse and process (do it
  yourself)
• Write a program using some libraries (DOM or SAX)
• Write processing rules using XSLT

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DOM Or SAX

• Libraries to parse XML data
• A Document Object Model (DOM) parser reads the
  whole source and converts it into a tree-like
  data structure
• A Simple API for XML (SAX) parser reads the
  source and allows the programmer to act on each
  element as soon as it is recognized
• DOM is easy to use, slow, and consumes memory
• SAX is harder to use, fast, and consumes less
  memory

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XSL And XSLT

• Process XML data using rules.
• The eXtensible Stylesheet Language (XSL) is used
  to format XML documents for display (e.g. in a
  browser)
• The eXtensible Stylesheet Language Transformation
  (XSLT) allows converting XML documents into any
  other format including XML, HTML

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SOAP

• SOAP Simple Object Access Protocol
• XML based standard
• Allows calling methods, functions, or procedures
  on a remote computer
• It works over the Internet
• Uses HTTP
• Can pass through a firewall
• Allows inter-operability between different
  platforms, operating systems, and languages

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Web Services

• A standard for locating SOAP methods and
  determining how to use them automatically
• Web Service Description Language (WSDL) A way to
  describe the remote methods name and parameters
• Universal Description, Discovery and Integration
  Protocol (UDDI) A directory listing of different
  services (like yellow pages)
• Web Service SOAP WSDL UDDI

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Thats It with XML Technologies
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Whats Next

• To learn more about XML
• www.xml.com
• www.ibm.com/developer/xml/
• www.xmlsoftware.com
• msdn.microsoft.com/xml/
• Book CodeNotes for XML
• Start using it. You can use
• VB, Java, .NET, C,
• MS, IBM, and Sun provide free XML parsers and
  libraries

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Examples

• RTRErrorLog.xml Error log file.
• RTRConfClient.xml A configuration file.
• XSLT On-line example.

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Feedback

• Did this satisfy your expectations?
• Any suggestions or comments?
• What topics do you like to see in a next or
  advanced class? (e.g. XSLT, SOAP, )