Introduction to XML

1
Introduction to XML

• Kostas Kontogiannis
• Evan Mamas

2
Outline

• Introduce XML, HTML and SGML
• Compare and Contrast
• XML vs. HTML
• XML vs. SGML
• XML
• Components, Applications, Industry
• Thoughts on XML

3
What is XML?

• eXtensible Markup Language
• Proper subset of SGML for web use
• Meta-language
• Allows you to create your own markup languages
• Compromise between HTML and SGML

4
What is HTML ?

• HyperText Markup Language
• Language to describe information for transmission
  over the web.
• Uses tags to markup the information
• Tags are just a formatting tool
• Example
• ltH1gt Hello, World lt/H1gt
• Hello, World

5
Why isnt HTML enough?

• Good enough for presenting text on the web
• Not accepted as an authoring or archival form
• Extensibility
• HTML standard changes continually
• Uses tags for formatting
• Structures
• Has no defined or definable structural rules

6
What is SGML ?

• Standard Generalized Markup Language
• International Standard for over 10 years
• Language for specifying markup languages
• Describes only the formal properties and
  inter-relations of the components of a document
• Document, Entities, Elements, Attributes

7
Uses of SGML

• Formally structured documents
• Technical Manuals
• Exchange documents
• Product documentation
• Data encoding
• Interchange specification
• Provide long-term storage of information which
  was independent of suppliers and changes in h/w
  and s/w

8
SGML Example

• Memo
• DTD (Document Type Definition)

lttogtAll staff ltfromgtMartin Bryan ltdategt5th
November ltsubjectgtCats and Dogs lttextgtPlease
remember to keep all cats and dogs indoors
tonight.
lt!DOCTYPE memo lt!ELEMENT memo O O ((to from
date subject?), text) gt lt!ELEMENT text - O
(para) gt lt!ELEMENT para O O (PCDATA)
gt lt!ELEMENT (to, from, date, subject) - O
(PCDATA) gt gt
9
Why isnt SGML enough?

• Specification is very long
• Contains many options not needed for Web
  applications
• Time consuming and high cost
• Expensive tools
• Too much for small applications
• Bad reputation

10
XML vs. HTML

• New tags and attributes definitions allowed
• Document structures can be nested to any level of
  complexity
• Structural validation is possible by describing
  the grammar

11
XML vs. SGML

• XML is the minimum required subset of SGML for
  web use
• Easier to implement and to create tools for
• A new attempt at structured markup languages with
  a new face

12
XML Components

• XML Style Language (XSL)
• Cascading Style Sheets, level 2 CCS2
• XML Document Object Model (DOM)
• XML Linking Language (XLL)
• XML Pointer Language (XPL)
• XML Name Spaces
• Synchronized Multimedia Integration Language
  (SMIL)
• Resource Description Framework (RDF)
• Mathematical Markup Language (MathML)

13
XML Components (cont.)

• XML Style Language (XSL)
• Defines a way to present the documents
• Separates formatting from content
• Has two steps
• Generate a result tree (associate patterns with
  templates)
• Use XML Namespace (formatting vocabulary) to
  generate formatted output.
• Similar to DSSSL for SGML

14
XML Components (cont.)

• Cascading Style Sheets, level 2 CCS2
• Defines a way to present documents
• Similar to XSL (Not as strong)
• Supported by most browsers

ltHTMLgt ltTITLEgtBach's home pagelt/TITLEgt
ltSTYLE type"text/css"gt H1
color blue lt/STYLEgt ltBODYgt
ltH1gtBach's home pagelt/H1gt
ltPgtJohann Sebastian Bach was a prolific
composer. lt/BODYgt lt/HTMLgt
15
XML Components (cont.)

• XML Document Object Model (DOM)
• In-memory model for representing parsed XML
  documents
• Designed to provide common structures in XML
  browsers
• Intended to enable interoperable XML processing
  across browsers
• Implemented by Internet Explorer and Netscape

16
XML Components (cont.)

• XML Linking Language (XLL)
• Links by reference rather than exact location
• Provides hyperlinking elements
• Simple links like HTML links
• Extended
• Multi-directional links
• Links with multiple destinations
• Placing content inline from a linked document
• Requires use of XML Pointer Language

17
XML Components (cont.)

• XML Name Spaces
• Vocabulary of all elements and attribute types
• Namespace prefix (mapped to Uniform Redource
  Identifier)
• Local Part
• Allows use of names defined in other documents
• Modularity and reuse of a markup
• Mechanisms to establish name scope

18
XML Components (cont.)

• Synchronized Multimedia Integration Language
  (SMIL)
• Language for describing interactive synchronized
  multimedia distributed on the Web
• Several components (images, video, audio) can be
  linked together to create a presentation on the
  web
• Resource Description Framework (RDF)
• Abstract mechanism for defining simple
  relationships among web resources
• Mathematical Markup Language (MathML)
• Language to describe mathematical expressions

19
XML DTD

• Defines the hierarchy of all user-defined
  elements (tags) in the XML document
• Declares the attributes and behaviour of each XML
  element
• Each XML document calls a specific DTD file to
  validate its elements

20
XML DTD

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!-- DTD for a simple program beginning of
  element declarations--gt
• lt!--the root tag of Language--gt
• lt!ELEMENT Language (FileTag,Declaration,Function
  _Call)gt
• lt!ELEMENT FileTag (IncludeTag,SourceTag)gt
• lt!ELEMENT IncludeTag (PCDATA)gt
• lt!ELEMENT SourceTag (PCDATA)gt
• lt!ELEMENT Declaration (Type_NameIdentifier)gt
• lt!ELEMENT Type_Name (PCDATA)gt
• lt!ELEMENT Identifier (PCDATA)gt
• lt!ELEMENT Function_Call (Return_Type,Function_Nam
  e,Argument)gt
• lt!ELEMENT Return_Type (Return_Var)gt
• lt!ELEMENT Return_Var (PCDATA)gt
• lt!ELEMENT Function_Name (PCDATA)gt

Defines what other tags are within the
ltLanguagegt tag
Defines data types for contents within the
ltIncludeTaggt tag
21
XML Document (page 1 of 2)

• lt?xml version"1.0"?gt
• lt?xmlstylesheet type"text/xsl"
  href"studentXSL1.xsl" ?gt
• lt!DOCTYPE Language SYSTEM "Student.dtd"gt
• ltLanguagegt
• ltFileTaggt
• ltIncludeTaggtinclude stdio.hlt/IncludeTaggt
• lt/FileTaggt
• ltFileTaggt
• ltIncludeTaggtinclude math.hlt/IncludeTaggt
• lt/FileTaggt
• ltFileTaggt
• ltSourceTaggtcode statement3lt/SourceTaggt
• lt/FileTaggt
• ltFileTaggt
• ltSourceTaggtcode statement2lt/SourceTaggt
• lt/FileTaggt
• ltDeclarationgt
• ltType_Namegtcharlt/Type_Namegt

Calls a XSL style sheet
Calls a DTD document
22
XML Document (page 2 of 2)

• ltDeclarationgt
• ltType_Namegtintlt/Type_Namegt
• ltIdentifiergtnumOfstudentslt/Identifiergt
• lt/Declarationgt
• ltDeclarationgt
• ltType_Namegtcharlt/Type_Namegt
• ltIdentifiergtfacultyNamelt/Identifiergt
• lt/Declarationgt
• ltFunction_Callgt
• ltReturn_Typegt
• ltReturn_Vargtstudent_profilelt/Return_Vargt
• lt/Return_Typegt
• ltFunction_Namegtelec_englt/Function_Namegt
• ltArgumentgt
• ltparameterNamegtnamelt/parameterNamegt
• lt/Argumentgt
• lt/Function_Callgt

23
XML Namespaces

• Latest milestone for W3C's XML technology
  (14-January-1999 )
• W3Cs definition of XML NameSpaces
• XML namespaces provide a simple method for
  qualifying element and attribute names used in
  Extensible Markup Language documents by
  associating them with namespaces identified by
  URI references.
• Why use it?
• Maintain tag meaningfulness and uniqueness
• How does it solve the problem?
• Add context to XML tags by using prefix and URL

24
XSL Document (Page 1 of 3)

• lt?xml version"1.0"?gt
• ltDIV xmlnsxsl"http//www.w3.org/TR/WD-xsl"gt
• lthtmlhtml xmlnshtml"http//www.w3.org/TR/REC-ht
  ml40"gt
• ltigtThis page consists of XML, XSL, Namespace,
  HTML, and Java Appletlt/igt
• lthtmlheadgtlthtmltitlegtltH1gtSample C Code (hidden
  XML tag)lt/H1gtlt/htmltitlegtlt/htmlheadgt
• ltxslfor-each select"Language"gt
• ltTD STYLE"padding-left1em"gt
• ltDIVgtltxslvalue-of select"/"/gtlt/DIVgt
• lthtmlfont color"red"gtThe above command
  prints out all contents within tags without any
  formmating, ordering, linebreaks,
  etc.lt/htmlfontgt
• lt/TDgt
• lt/xslfor-eachgt
• ltxslfor-each order-by" IncludeTag"
  select"Language/FileTag"gt
• ltTD STYLE"padding-left1em"gt
• lthtmlBRgtlt/htmlBRgt
• ltDIVgtlthtmlBRgtltxslvalue-of select"IncludeTag"/
  gtlt/htmlBRgtlt/DIVgt
• lt/TDgt

Namespace for XSL
Namespace for HTML
25
XSL Document (Page 2 of 3)

• ltxslfor-each order-by" SourceTag"
  select"Language/FileTag"gt
• ltTD STYLE"padding-left1em"gt
• lthtmlBRgtlt/htmlBRgt
• ltDIVgtltxslvalue-of page-break-after"SourceTag"
  select"SourceTag"/gtlt/DIVgt
• lt/TDgt
• lt/xslfor-eachgt
• lthtmlfont color"red"gtEnd of SourceTag,
  ascending sort on SourceTag Contentlt/htmlfontgt
• lthtmlBRgtlt/htmlBRgt
• ltxslfor-each order-by" Type_Name"
  select"Language/Declaration"gt
• ltTD STYLE"padding-left1em"gt
• lthtmlBRgtlt/htmlBRgt
• ltDIVgtlthtmlBRgtltxslvalue-of select"Type_Name"/gt
  lt/htmlBRgtlt/DIVgt
• ltDIVgtlthtmlBRgtltxslvalue-of select"Identifier"/
  gtlt/htmlBRgtlt/DIVgt
• lt/TDgt
• lt/xslfor-eachgt
• lthtmlfont color"red"gtEnd of Declaration,
  ascending sort on Type_Namelt/htmlfontgt
• ltDIVgtlt/DIVgt

26
XSL Document (Page 3 of 3)

• ltxslfor-each select"Language/Function_Call"gt
• ltTD STYLE"padding-left1em"gt
• lthtmlBRgtltDIVgtltxslvalue-of select"Return_Type"
  /gtlt/DIVgtlt/htmlBRgt
• lthtmlfont color"red"gtEnd of
  Return_Typelt/htmlfontgt
• lthtmlBRgtltDIVgtltxslvalue-of select"Function_Nam
  e"/gtlt/DIVgtlt/htmlBRgt
• lthtmlfont color"red"gtEnd of
  Function_Namelt/htmlfontgt
• lthtmlBRgtlt/htmlBRgt
• lthtmlBRgtltDIVgtltxslvalue-of select"Argument"/gtlt
  /DIVgtlt/htmlBRgt
• lthtmlfont color"red"gtEnd of
  Argumentlt/htmlfontgt
• lthtmlBRgtlt/htmlBRgt
• lt/TDgt
• lt/xslfor-eachgt
• lthtmlBRgtlt/htmlBRgt
• lthtmlAPPLET code"AgentAction.class" width"400"
  height"200"gtlt/htmlAPPLETgt
• lthtmlBRgtlt/htmlBRgt
• lt/htmlhtmlgt

27
Applications that require XML

• Information exchange between heterogeneous
  databases
• Health care example
• Distributed processing
• Semiconductor industry example
• Multiple views of the same data
• Intelligent information agents

28
Using XML

• XML for Storage
• Compact syntax
• Generalized and standarized
• Product independent
• XML for Searching
• Use of content specific markup enables robust
  searching
• Search engines need to be XML aware
• Can use current SGML search engines

29
What is DOM?

• A programming API for XML
• logical structure of document
• Access and Manipulation of documents

30
What is DOM?

• As an object model, DOM identifies
• Interface and Objects used for the doc.
• Behaviours and Attributes
• Relationships and Collaborations of Interfaces
  and Objects

31
What is DOM?

• 2 Major Components for DOM Level 1
• DOM Core Basic functionalities for XML
• DOM HTML Objects and Methods specific to HTML
• Level 2
• DOM CSS, DOM Event, DOM Filters and Iterators,
  DOM Range

32
Advantages of using DOM

• Easy to create, navigate, add, modify documents
• DOM abstraction avoids implementation
  dependencies
• DOM applications may use additional language
  bindings

33
A Typical DOM Structure

• ltcondition_statementgt
• ltif_statementgt
• ltif_taggt if lt/if_taggt
• ltexpression_taggt (b c) lt/expression_taggt
• ltstatement_taggt a c lt/statement_taggt
• lt/if_statementgt
• lt/condition_statementgt

34
A Typical DOM Structure (2)
35
A Typical DOM Structure (3)

• DOM abstraction is a Tree or Forest Structure
• Users have full flexibility to specify the
  structure
• Structural Isomorphism

36
Some Key Objects

• Node
• Tree node of the document
• root node, parents and children
• Element (is a Node object)
• Elements of a document
• Represents contents between the start tag and end
  tag
• Attributes defined by DTD

37
Some Key Objects (2)

• Document
• root node of a document
• NodeIterator
• iterates over a set of nodes specified by a
  filter
• AttributeList
• collection of Attribute objects, indexed by
  attribute name

38
Some Key Objects (3)

• Attribute
• attribute of an Element Object
• DocumentContext
• respository for metadata about a document
• DOM
• provides instance-independent document operations

39
Memory Management for DOM

• DOM APIs operate across a variety of memory
  implementation methods
• Language platforms that do not expose memory
  management to user
• Language (Java) that provides constructors with
  Garbage collection capability
• Language (C/C) that requires explicit memory
  allocations

40
Resources/Quirks

• IE 5 and Navigator 5.0 implement different
  features
• IE 5.0 - XML/XSL Navigator - XML/CSS
• Navigator to support RDF
• XML Resources
• http//www.swen.uwaterloo.ca/group1

41
Using XML (cont.)

• XML for Presentation
• Convert to HTML at server
• Use Java applications to render in browser
• Slow
• Use XSL or CSS to render in browser
• Fast

42
XML in the industry

• Explosive growth of XML tools and specifications
• Tools JADE, MSXML, JUMBO,...
• Specifications CDF, CFML,EDI
• Browsers IE, Netscape

43
Thoughts on XML

• Seems like a transition stage between HTML and
  SGML
• Will we eventually end up using SGML?
• XML follows basic principles of SE
• Higher abstraction layer
• Reuse
• Modularity

44
References

• XML.COM - A guide to XML
• http//www.xml.com/xml/pub/w3j/s3.walsh.html
• XML.COM - The Road to XML Adapting SGML to the
  Web
• http//www.xml.com/xml/pub/w3j/s1.discussion.html
• The Computer Bulletin - The XML Files
• http//www.bcs.org.uk/publicat/ebull/may98/xml.htm
  
• XML, Java, and the future of the Web
• http//sunsite.unc.edu/pub/sun-info/standards/xml/
  why/xmlapps.htm
• XML What is it
• http//iai.sgml.com/980106-01.asp
• Why do we need XML?
• http//info.admin.kth.se/SGML/Konferenser/xml98sve
  /seminar.html
• An Introduction to the Standard Generalized
  Markup Language
• http//www.personal.u-net.com/sgml/sgml.htm
• SGML101
• http//www.uslynx.com/sgml101.htm