xml

							XML
A brief introduction

        ---by Yongzhu Li
                                               SUNY Albany Computer Science Department




      XML
          eXtensible Markup Language
          designed to describe data.
          a family of technologies
          platform-independent
          free and extensible



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   Basic Concept
           a markup language is a mechanism to
           identify structures in a document.
           the XML specification defines a
           standard way to add markup to
           documents.
           a meta-language for describing markup
           languages
           provides a facility to define tags and
           the structural relationships between
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                                --- a brief introduction 3
                                               SUNY Albany Computer Science Department



      Background
          SGML
               Standard Generalized Markup Language (ISO
                8879)
               provides arbitrary structure, but too difficult to
                implement just for a web browser.
          HTML
               A subset of SGML with a fixed tag semantics
                and set, lack of flexibility and extensibility
               Lack of extensibility


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      Background II
          XML
               simplified SGML, extensible
               looks like HTML but isn't HTML
               any fully conformant SGML system will
                be able to process XML documents
               but, XML documents does not require a
                system that is capable of the full
                conformance of SGML

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      Evolving History
          W3 Consortium began work in Aug.
          1996
          XML 1.0
               Released by W3C on Jan. 10, 1998
          XML 2.0
               Introduced on Oct. 6, 2000
          XML 3.0
               Under drafting and evaluating
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      What XML looks like
          prolog --- XML file declaration
               <?xml version=“1.0”?>
          comment
               <!-- any comments -->
          processing instruction, PI
               <?xml-stylesheet type="text/css"
                href="first.css"?>
          element and its attribute
               <price currency ="$">15.50</price>

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      First Sample
           a single XML document
                                                            single XML file
                                                             only provide
                                                             structured data
                                                            No formatting
                                                             information
                                                            browser don’t
                                                             know how to
                                                             display

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Topics in System Architecture     --- a brief introduction
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                                  CSS
           Cascading Style Sheets
           also work well with HTML
           delaring CSS within XML file
               <?xml-stylesheet type="text/css"
                href="first.css"?>
          separate data content with its form
          only provide formatting information,
          lack of manipulation on data
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Topics in System Architecture     --- a brief introduction
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      First Sample II
         Formated Source CSS file




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      Interesting CSS
          Cascading layers                                   sample
               z-index                                      XML
                                                             CSS
               position




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      Interesting CSS II
          Filter                                     sample
               filter:glow(color=blue, Strength=5); XML
                                                     CSS




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      XSL
          eXtensible Stylesheet Language
          declaring XSL within XML
               <?xml-stylesheet type="text/xsl" href="first.xsl"?>
          transform XML to HTML file
          defining and formating XML parts
          and patterns
          far more sophisticated but powerful
          than CSS

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Topics in System Architecture      --- a brief introduction
                                               SUNY Albany Computer Science Department




      XSL by Sample
           Data Sorting XSL Source
           Data Filter XSL Source




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      Namespace
          a collection of element type
          and attribute names
          distinguish between
          duplicate element type and
          attribute names


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      Namespace Samples
         <books xmlns:book=“books.dtd”
         xmlns:journal =“journal.dtd”>
            <book:title>
                   …..
            </book:title>
            <journal:title>
                    …..
            </journal:title>
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      Name Space Sample II
          <html
          xmlns:html=“http://www.w3.org/TR/R
          EC-html40”>
           <html:h1>some message</html:h1>
           <html:a href=
            mailto:yongzhu@cs.albany.edu>
            email me</html:a>

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      DTD
         Documents Type Definition
         a model for describing the
         structure of information.
         Well formed XML and Valid
         XML
         A valid XML must follow a
         specific DTD
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      Why DTD
           Independent organizations
          use a common DTD for
          interchanging data.
           applications use DTD to
          verify the data received from
          the outside world is valid.
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    Eric:                                      SUNY Albany Computer Science Department
  Parsable

      DTD II
Character Data


            Declaring DTD within XML
             <!DOCTYPE books SYSTEM

              “book.dtd”>
            Element Declaration within DTD
             <!Element title (#PCDATA)>

             <!Element book (title,author+, press,
              price)>
             <!Element books (book*)>

            Attribute Declaration
             <!ATTLIST price currency ($|€|¥)’$’>
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Topics in System Architecture     --- a brief introduction
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      DTD Weakness
          written in a different (non-XML)
          syntax.
          don’t support namespace
          only offer extremely limited data
          types.
          have a complex and fragile
          extension mechanism
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      Schema
         replacement of DTDs for XML
         more primitive data types
         namespace support.
         itself is a well formed XML
         and validated by Schema
         DTDs
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     XML Application Domain
          Electronic Data Interchange
          search engine
          web application
          distributed documentation
          and computing
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      Some other XML
      applications
         WML, Wireless Markup Language
         CML, Chemistry Markup Language
         and MathML
         OSD, Open Software Description
         OFX, Open Financial Exchange

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XML Application Structure
                                             CSS/ XSL
            Viewer #1                       translation
                                                                   Viewer #2
        e.g. Retail Agent
                                                                e.g. Customer

CSS/ XSL                           XML Processor
translation                                                     Other process
                                    Application Server


                    DB 1            DB 2       DB ..     DB n
                                May be heterogeneous DBs
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      DOM
          Document Object Model
          program interface for XML
          represents a tree view of the XML
          documentElement as a root
          childNode for other branch
          each node is an object
               Node Interface Model

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Topics in System Architecture     --- a brief introduction
                                               SUNY Albany Computer Science Department



      SAX
          the Simple API for XML
          another programming interface for
          XML
          event-based API
          use call-back functions to handle
          parsing event
          SAX and DOM are two major APIs for
          XML application development.

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Topics in System Architecture     --- a brief introduction
                                               SUNY Albany Computer Science Department



      SVG
          Scalable Vector Graphic
          XML application
          describe two-dimensional vector
          graphic shapes, images and text
          reduced the network traffic
          reduced server overload
          VML by Microsoft and PGML by
          Adobe
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Topics in System Architecture     --- a brief introduction
                                               SUNY Albany Computer Science Department



      XHTML
           eXtensible HTML
           HTML defined by XML
           well-formed HTML
           tag names must be in lowercase



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Topics in System Architecture     --- a brief introduction
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      Things under going…
         Xlink and Xpointer
              allows elements to be inserted into XML in order
               to create and describe links between resources
              provide multi-directional hypertext and hypermedia
               support
              proposal recommendation on Dec. 20, 2000
         XML Protocol
              to develop technologies which allow two or more
               peers to communicate in a distributed
               environment, using XML as its encapsulation
               language.
              requirement draft on Dec. 19, 2000
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Thank You

        谢谢