XML for Beginners

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XML for Beginners

• Whys, Whats, Hows

2
HTML

• Hypertext Markup Language
• Used to apply structural markup
• Limited number of tags
• Not extensible (cannot create new tags/elements
  on the fly, so machine readable)
• Employs attributes
• May employ scripting (JavaScript, etc.)
• May employ cascading style sheets (CSS)
• Used for the web, HTML help, etc.
• ANSI text file

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Defining XML

• The Extensible Markup Language (XML) is a subset
  of SGML. Its goal is to enable generic SGML to be
  served, received, and processed on the Web in the
  way that is now possible with HTML. XML has been
  designed for ease of implementation and for
  interoperability with both SGML and HTML.

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XML, SGML, HTML

• XML is a profile of SGML.
• XML is less complex than SGML but more complex
  than HTML.
• It has been said that XML provides 80 of the
  benefit of SGML with 20 of the effort.

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What is XML?

• XML stands for EXtensible Markup Language
• XML is a markup language much like HTML
• XML was designed to describe data
• XML tags are not predefined. You must define your
  own tags
• XML uses a Document Type Definition (DTD) or an
  XML Schema to describe the data
• XML with a DTD or XML Schema is designed to be
  self-descriptive

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Difference between XML and HTML

• XML was designed to carry data
• XML is not a replacement for HTMLXML and HTML
  were designed with different goals
• XML was designed to describe data and to focus on
  what data is.HTML was designed to display data
  and to focus on how data looks.
• HTML is about displaying information, while XML
  is about describing information.

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XML

• Extensible Markup Language
• Semantic markup applied
• Extensible any type of element can be used
• Must be valid and structured to work
• May employ attributes
• May employ XSL for transform, format
• Standardized text format designed specifically
  for transmitting structured content to web
  applications
• Unambiguous easy to understand hierarchy
• Elements have parent-child relationship
• Unicode text file
• Able to validate in IE with the proper tools
• Strict formatting against DTD
• Can be sorted easier than HTML

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The design goals for XML

• XML shall be straightforwardly usable over the
  Internet.
• Supported by browsers
• Platform independent
• XML shall support a wide variety of applications.
• XML shall be compatible with SGML.
• It shall be easy to write programs which process
  XML documents.
• The number of optional features in XML is to be
  kept to the absolute minimum, ideally zero.
• But the number of absolute requirements are
  global and few in number

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The design goals for XML

• XML documents should be human-legible and
  reasonably clear.
• Human legible humans can read them, but not
  necessarily that all humans can interpret them
• Humans do not have to have specific applications
  (other than a text editor) to look at an XML file
  in order to make sense of it.
• The XML design should be prepared quickly.
• XML editors have evolved, however, that make this
  much easier.
• Its like the difference between hard-coding html
  and using an html editor.
• The design of XML shall be formal and concise.
• XML documents shall be easy to create.
• Terseness in XML markup is of minimal importance.

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Why XML

• HTML standards change too slowly.
• Html 3.2 and 4.0, but further development slow.
• Difficulty of constraining everyone to use the
  same set of rules.
• XML solution
• Flexible framework that allows the users to
  declare their own sets of constraints.
• Within a high-level limited set of very demanding
  rules.

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HTML vs. XML

• HTML 3.2 together with CGI scripts, Java applets,
  and JavaScript (and its derivatives), plus
  plug-ins such as Shockwave, RealPlayer, and
  Quicktime provide Web authors and commercial
  sites with a rich array of techniques for
  displaying content that is visually compelling
  and possibly even informative. However, these
  techniques do little if anything for the
  representation of structured data unless one
  introduces middleware solutions.

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Why XML

• Browser-specific markup impairs the concept of a
  world-wide web that is universal platform
  independent.
• Browser-specific extensions to the rules.
• Difficulties in getting all options to display in
  all browsers.
• The great browser wars (Microsoft vs. Netscape,
  Opera, etc.)

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Why XML

• HTML is incapable of delivering web-enabled
  applications.
• Web-based working environments
• Group authoring in distributed environments
• Group database management in distributed
  environments (example multilingual terminology
  and TM database initiatives)
• Lean-client, web-server-based applications

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Why XML

• Search engines return too many hits.
• Use of axiom-based ontology resources (OWL
  environment) instead of keyword-based searches
• Enabling inference-based computing on the Web
• Expansion of the depth of metadata that can be
  associated with specific pages and sets of
  information
• Metadata initiatives
• RDF development
• Dublin core
• EPA, Institutes of Health, Terminology data
  management, etc.

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Why XML Character Encoding

• HTML is based on ISO 8859
• 15 parts multiple pages, each for a different
  block of characters
• Impossibility of encoding for multiple, divergent
  sets (e.g., for ru, en, ch at the same time)
• XML is based on UNICODE
• The Unicode Standard  Unicode defines the
  universal character set. Its primary goal is to
  provide an unambiguous encoding of the content of
  plain text, ultimately covering all languages in
  the world.
• http//www.unicode.org/standard/WhatIsUnicode.html
  
• http//www.w3.org/TR/unicode-xml/
• Unicode in XML and Other Markup Languages

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Examples HTML

• ltBgtJohn Q Publiclt/Bgt ltPgt john.q.public.1_at_gsfc.nas
  a.govltBRgt phone 301-286-aaaaltBRgt fax
  301-286-bbbbltBRgt Bldg. 23, Rm. 999ltBRgt NASAltBRgt
  Goddard Space Flight CenterltBRgt
  588.0ltBRgtGreenbelt, MD 20221ltBRgt

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Example XML

• ltEMPLOYEEgt
• ltNAMEgt ltFIRSTgtJohnlt/FIRSTgt ltMIDDLEgtQlt/MIDDLEgt
  ltLASTgtPubliclt/LASTgt lt/NAMEgt ltEMAILgtjohn.q.public.1
  _at_gsfc.nasa.govlt/EMAILgt ltPHONEgt301-286-aaaalt/PHONE
  gt ltFAXgt301-286-bbbblt/FAXgt ltLOCATIONgt
  ltBUILDINGgtBldg. 23lt/BUILDINGgt ltROOMgt999lt/ROOMgt
  lt/LOCATIONgtltADDRESSgt ltORGgtNASAlt/ORGgt
• ltCENTERgtGoddard Space Flight
  Centerlt/CENTERgt ltMAILSTOPgt588.0lt/MAILSTOPgt
  ltCITYgtGreenbeltlt/CITYgt ltSTATEgtMDlt/STATEgt
  ltZIPgt20221lt/ZIPgt
• lt/ADDRESSgt
• lt/EMPLOYEEgt

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Advantages of XML

• XML preserves the semantics and structure of
  data.
• XML presents information as hierarchical data.
• XML data can be parsed and processed in the same
  way that you can process application-specific
  database data.
• But because it is human-readable, e.g.,
  universally accessible and uncompiled data, it
  can be accessed and used by a variety of
  different systems.

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XML Criteria

• An XML document must be well-formed.
• An XML document must be valid against its DTD,
  schema, or internally declared values.
• Declaration of legal tags
• Declaration of legal attributes
• Declaration of legal attribute values
• Declaration of permissible instances

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Well-formedness

• End tags must be present
• Nested tags must not overlap
• All tags and attributes must be lowercase (xml is
  case-sensitive)
• Use of quote marks for attribute values is
  required, as is consistent use of single or
  double quotes
• End tags or end markers are required, even for
  empty tags
• http//www.w3.org/TR/xhtml1/h-4.1

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Validity

• A DTD or schema defines specific rules
• Writers of valid documents follow these rules in
  addition to well-formedness constraints
• Two-part checking well-formedness validity
  check
• Functionality provided by Internet Explorer 6
• http//msxml.com/xml_tutorial/valid-xml.html

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xmllang

• Universal locale-oriented language code
• Country code language code

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Viewing an XML document in IE