XML Fundamentals

1
XML Fundamentals

• Jie Liu, Ph.D.
• Professor
• Department Of Computer Science
• Western Oregon University
• Monmouth, OR 97361
• Liuj_at_wou.edu

2
Outline

• XML Background
• Document Type Definitions
• Style Sheets and Process
• Other XML Related Technologies
• Summary
• Where to go for more help

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Beginnings of XML

• XML( eXtensible Mark-up Language) was developed
  by a working group of the World Wide Web
  Consortium (W3C) to bring Standard Generalized
  Markup Language (SGML) to the web
• XML is a faster, slimmed-down version of SGML
  designed for use on the Web
• First appeared in 1996
• SGML was 10 years old at this time
• The first official XML specification is published
  in February 1998

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XML

• XML
• Primary function is to describe and contain data
• Extensible to allow for describing and defining,
  virtually, any kind of data
• Separates the data from the presentation
• Well-Formed files
• XML files are case sensitivity

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XML Suits Many Applications

• XML is used in many applications that primarily
  involve
• Complex document creation
• Uses language similar to HTML to provides a
  richer set of document elements that is virtually
  unlimited
• Data exchange and database connectivity
• Used to define an interchange format suitable for
  data transfer between databases from different
  vendors on different operating systems

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XML Benefits

• Benefits of XML
• Structured data - XML handles data
• Style sheets can handle presentation
• Complements HTML
• XML data can be presented using an HTML page
• No predefined tags
• You make up the tags - or more properly, elements
• Self-describing
• A dictionary of tag definitions can be provided
  for wide use
• Requires precise rules to define the structure of
  a document
• Processing is easier with strict rules to follow

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A Simple Example of XML

• lt?xml version"1.0" standalone"yes"?gt
• ltKennelClub locationNortheast USA"gt
• ltBreedgtDobermanlt/Breedgt
• ltCategory nameworking" /gt
• ltFeaturesgt
• ltTraitgtlong straight earslt/Traitgt
• ltTraitgtshort taillt/Traitgt
• ltTraitgtshort hairlt/Traitgt
• ltTraitgtloyal to an individuallt/Traitgt
• lt/Featuresgt
• ltTrainingInstructionsgt
• Make use of a strong steel chain collar.
• Keep the dog on your left, walk with even
  steps.
• When stopped, the dog should sit beside
  you.
• lt/TrainingInstructionsgt
• ltFeedingInstructionsgt
• After 1 year of age, two cans of wet food
  mixed with 1 can of dry food.
• Provide a constant supply of water.
• Raise the feeding dish to the dogs
  shoulder height.

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Road Map

• XML Background
• Document Type Definitions
• Style Sheets and Process
• Other XML Related Technologies
• Summary
• Where to go for more help

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Document Type Definitions (DTD)

• Is a set of rules that defines the elements, and
  their attributes, of one or more XML documents
• Not required, but recommended for complex
  documents
• Advantages
• Create rules that many XML documents will follow
• Explicitly define the markup and rules for
  documents
• Provide a common frame of reference that can be
  shared

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Sample Document DTD

• lt!-- Begin bookcatalog.dtd --gt
• lt?xml version1.0 standaloneyes?gt
• lt!DOCTYPE Catalog
• lt!ENTITY bpl Boston Public Librarygt
• lt!ELEMENT Catalog (Book)gt
• lt!ELEMENT Book (Title,Author,Publisher,PubDate)
  gt
• lt!ELEMENT Title (PCDATA)gt
• lt!ATTLIST Title ISBN CDATA REQUIREDgt
• lt!ELEMENT Author (PCDATA)gt
• lt!ATTLIST Author Status CDATA IMPLIEDgt
• lt!ELEMENT Publisher (PCDATA)gt
• lt!ELEMENT Pub_Date (PCDATA)gt
• gt

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Sample Document Body

• lt!-- Begin Document Body --gt
• ltCataloggt
• ltBookgt
• ltTitle ISBN1201823764gtUNIX for the
  Impatientlt/Titlegt
• ltAuthor StatusactivegtPaul W. Abramslt/Authorgt
• ltPublishergtAddison-Wesleylt/Publishergt
• ltPubDategt1993lt/PubDategt
• lt/Bookgt
• ltBookgt
• ltTitle ISBN1565920546"gtThe Korn Shelllt/Titlegt
• ltAuthor Status"deceased"gtBill
  Rosenblattlt/Authorgt
• ltPublishergtOReilly Associateslt/Publishergt
• ltPubDategt1994lt/PubDategt
• lt/Bookgt
• lt/Cataloggt

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Document Type Declaration

• An internal document type definition
• lt!DOCTYPE Catalog
• The DTD information is contained within the
  document
• The name Catalog must identify the root element
  in the XML document
• Example of an external document type definition
• lt!DOCTYPE Catalog SYSTEM catalog_file.dtdgt
• Identifies Catalog as the root element
• Instructs the processor to fetch the external
  document called catalog_file.dtd, which is a
  relative path name to the dtd

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Why Have a DTD?

• Reasons to have a DTD
• They allow you to create rules for all documents
  to follow
• They clarify what markup may be used and how that
  markup should be sequenced
• They provide a common frame of reference that may
  be shared by many users
• Disadvantages of having a DTD
• May not have value when working with a few small
  documents
• Some processors are non-validating DTD not
  needed
• The DTD itself is NOT in XML syntax, making
  processing and understanding it like parsing
  another language
• Cannot be mixed

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Namespace Schema

• Namespaces helps XML vocabulary designers to
  break complex problems into smaller pieces and
  mix multiple vocabulary as needed.
• Schema permit vocabulary designers to create a
  more precise definition of the vocabulary than
  possible with DTDs and do so using XML syntax.

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Road Map

• XML Background
• Document Type Definitions
• Style Sheets and Processing
• Other XML Related Technologies
• Web Services
• Summary
• Where to go for more help

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Introducing Style Sheets

• Extensible Stylesheet Language (XSL)
• not only control presentation,
• but provide much more, including
• the functionality of a scripting language
• transform XML to HTML
• transform XML into XML.
• The output DTD can be different from the source
  DTD

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More about XSL

• Extensible Stylesheet Language - XSL
• Similar to CSS but much more powerful
• Is created for XML
• XSL style sheets are XML documents
• Made up of three parts
• Language for transforming XML documents - XSLT
• Language for specifying parts of XML documents -
  XPath
• Vocabulary for specifying formatting properties -
  XSLFO
• XSLT and XPath are standards

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The Document Object Model, DOM

• A programming interface
• Uses standard syntax to describe a document
• Allows for the manipulation of XML documents
• Creating XML documents
• Transforming XML documents
• Importing Data
• Accessed by many languages
• C
• JavaScript
• VBScript
• Java
• VB
• C

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The Document Object Model (cont.)

• A DOM is created each time an XML processor
  parses a document
• Parsing result is stored as objects
• DOM objects, called Nodes, can be access and
  manipulate

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Simple API for XML (SAX)

• Offers events as it parses the document
• Does not retain the document
• Makes minimal demands on system resources
• Benefits
• It can parse files of any size, simple, and fast
• It is useful when
• You want to build your own data structure
• Only want a small subset of the information
• You system has limited resources

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Simple API for XML (SAX)

• Drawbacks
• No random access to the document
• Is difficult to implement complex searches
• The DTD is not available
• Lexical Information is not Available
• Is Read-only
• Not support in some browsers

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Road Map

• XML Background
• From HTML to XML
• Document Type Definitions
• Style Sheets and Process
• Other XML Related Technologies
• Summary
• Where to go for more help

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Other Related Technologies

• XML Linking Language (Xlink) specification
  provides a framework for creating both
• XML Pointer Language (XPointer) specification
• Supports addressing into the internal structures
  of XML docs
• Built on top of the XML Path Language XPath
• The XML Query group is drafting a specification
  to produce XQL to query an XML document

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Other Related Technologies (cont.)

• XML Schema Structures definition proposing
  facilities for
• Describing the structure of XML documents
• Constraining the contents of XML documents
• Providing a superset of the capabilities found in
  DTDs
• XML Schema Datatypes definition proposing
  facilities for
• Defining datatypes to be used in XML Schemas and
  other XML specifications
• Providing a superset of the capabilities found in
  DTDs for specifying datatypes on elements and
  attributes
• The language description is, itself, an XML
  document

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Summary

• SGML is the foundation for HTML and XML
• HTML is an application for display of data
• XML is an extensible language for describing data
• Is not difficult to transition HTML knowledge to
  XML use
• Document Type Definitions, DTDs, describe the
  elements and attributes of XML documents and
  define their use.
• Schema is more powerful
• Style Sheets provide the ability to format and
  display data described with XML
• The Document Object Model, DOM, is a programming
  interface for accessing and manipulating elements
  and attributes of XML documents
• There are many other XML Related Technologies,
  web services is the most important one!

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A Question

• An XML document can be Well-formed but not valid
  what does this mean?

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Where to Go For More Help - 1

• General XML references
• W3C's XML Page - www.w3.org/XML
• XML.com - www.xml.com
• XMLInfo -www.xmlinfo.com
• Parsers and validation references
• Robin Cover's Check or Validate XML page
• www.oasis-open.org/cover/check-xml.html
• IBM's DOMit Validation Servlet
• www.networking.ibm.com/xml/XmlValidatorForm.html
• Microsoft's XML Validation page
• http//msdn.microsoft.com/downloads/samples/intern
  et/xml/xml_validator

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Where to Go For More Help - 2

• XML.com RUWF? Page
• www.xml.com/pub/tools/ruwf/check.html
• XML.com parse page
• www.xml.com/pub/Guide/XML_Parsers
• DTD and Style Sheet references
• Lumeria Network's Web-based DTD service
• www.dtd.com
• Cascading Style Sheets page at the W3C
• www.w3.org/Style/css
• CSS1 Specification
• www.w3.org/TR/REC-CSS1

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Where to Go For More Help - 3

• CSS2 Specification
• www.w3.org/TR/REC-CSS2/selector.html
• Web Design Group's CSS tutorials
• www.htmlhelp.com/reference/css
• WebMonkey's CSS tutorials
• www.hotwired.com/webmonkey/stylesheets
• Webreview's CSS articles
• webreview.com/wr/pub/Style_Sheets
• XSL page at the W3C
• www.w3.org/Style/XSL
• XSLT Recommendation
• www.w3.org/TR/xslt -TE

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Where to Go For More Help - 4

• XSLInfo
• www.xslinfo.com
• Document Object Model references
• DOM 1.0 Recommendation
• www.w3.org/DOM
• Converting XML documents to HTML using the DOM
• msdn.microsoft.com/xml/XSLGuide/default.asp Other
  related technology references
• XPath Recommendation
• www.w3.org/TR/xpath
• XPointer Recommendation
• www.w3.org/TR/WD-xptr
• SAX references
• http//www.megginson.com

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Where to Go For More Help - 5

• W3C's mailing list page
• www.w3.org/XML/discussion
• Some great tools on the web
• ADEPT Editor -www.arbortext.com
• CLIP! Editor -www.t2000-usa.com
• XMetaL -www.xmetal.com
• XML Pro -www.vervet.com
• AElfred -www.microstar.com
• expat -www.jclark.com
• SP -www.jclark.com
• LARK -www.texuality.com
• XML4J Parser -www.alphaworks.ibm.com

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Where to Go For More Help - 6

• Amaya -www.w3.org/Amaya
• Jumbo -www.xml-cml.org/jumbo
• Mozilla -www.mozilla.org
• POET Software -www.poet.com
• Microsoft's XML tools -www.microsoft.com/xml
• webMethods B2B -www.webmethods.com
• XML Software -www.xmlsoftware.com