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					Cs105 – Computer Concepts

               Module 4 - XML
          Instructor: Dan Pletea
                UMASS Boston
               What is XML?
•   XML stands for Extensible Markup Language.
•   XML is a markup language like HTML.
•   XML was designed to describe data.
•   You must define your own tags.
         An XML Example
<note>
<to>John</to>
<from>Merry</from>
<heading>Reminder</heading>
<body>Don’t forget to pick up the
  box</body>
</note>
               Why XML?
• There is a huge number of websites on the
  web and each website posts tunes of web
  pages. Also the number of web sites
  increases day by day.
• It is getting harder to find the information
  we are looking for.
               Why XML?
• We need search engines to locate the
  information that we are looking for.
• Most of the WWW documents are in
  HTML.
• Search engines can bring you tons of pages.
• Note that we humans are smart. Most of the times
  we can realize the content of a webpage by
  reading it. But computer programs are not and
  search engine is a computer program.
        XML is the solution.
• HTML describes how to display a page.
• But it does nothing to describe the contents
  of a page.
• We need a language to convey the content
  of a web page.
• XML is the solution.
                    XML
• XML indicates:
  – What information is contained within a
    webpage.
  – Where that information is on the page.
          XML and HTML
• XML is not a replacement for HTML
• XML was designed to describe data in a
  format that you want and to focus on what
  data is.
• HTML was designed to display data in a
  format that you prefer.
• HTML is about displaying information,
  while XML is about describing information
         XML and HTML
• XML and HTML complement each other.

        XML describes the data.

        HTML displays the data.
    eXtensible Markup Language
• eXtensible
• Markup
• Language
• XML is supported by many platforms and
  many tools.
• A lot of web applications are using XML
  now.
                         XML vs. HTML
<HTML>
                                   <RECIPE>
<BODY>                             <INGREDIENTS>
  <UL>                                <INGREDIENT> 1Kg apple </INGREDIENT>
    <LI> 1 kg apple                   <INGREDIENT> 1/2Kg Sugar </INGREDIENT>
    <LI> 1/2 Sugar                    <INGREDIENT> 1 kg white flour </INGREDIENT>
    <LI> 1 kg white flour             <INGREDIENT> 250 g butter </INGREDIENT>
    <LI> 250 g butter              </INGREDIENTS>
                                   <INSTRUCTIONS>
  </UL>
                                      <INSTRUCTION> Place apples in a bowl.
  <P> Place apples in a bowl.
                                      </INSTRUCTION>
  Toss with flour until covered.
                                        <INSTRUCTION> Toss with flour until covered.
   then, ...
                                      </INSTRUCTION>
 </BODY>                                ….
</HTML>                            </INSTRUCTIONS>
                                   </RECIPE>
                   XML
• Labels the data
• Structures the data
• Example
 Rules for Well-Formatted XML
• Every XML document must have a special tag:
  <?xml version=“1.0”?> to tell web browser it is an
  xml file
• Every XML document must have a single, all-
  enclosing “root tag”
• Every XML element must have a corresponding
  closing tag
• Just as HTML, XML elements must be properly
  nested
• XML tags are case sensitive, <FOOD> and
  <food> are different
• The value of an attribute must appear in quotation
  marks (either double or single quotation marks
  work)
       XML Element Names
• Names can contain letters, numbers and
  other characters
• Names cannot begin with a number or an
  underscore
• Names cannot begin with the prefix “XML”
  or “xml” or “xML” etc.
• Names cannot contain spaces
    Good, Bad, and Unparsable
• Common errors in XML: misspelling tag names,
  have more than one root-level element, forgetting
  to close an open quote
• If XML file is well-formed, the browser will
  display the file in a hierarchical fashion,
  otherwise, cannot load the file
• The XML file could be designed poorly although
  it is well-formed.
    Good, Bad and Unparsable
• Bad example:
<TVGuide>
  <channel>…</channel>
  <time>…</time>
  <title>…</title>
  <description>…</description>
  <channel>…</channel>
  <time>…</time>
  <title>…</title>
  <description>…</description>
</TVGuide>
      Good, Bad and Unparsable
• Solution:
<TVGuide>
   <program>
        <channel>…</channel>
        <time>…</time>
        <title>…</title>
        <description>…</description>
   </program>
   <program>
        <channel>…</channel>
        <time>…</time>
        <title>…</title>
        <description>…</description>
   </program>
</TVGuide>
                      Design Tips
• Think logically and design accordingly
Ex. Use <CD>…</CD> for cd collections
• If you want it, tag it
Ex. Don’t use <Time>10:00pm
                        <name>..</name>
              </Time>
Use <Time> <slot>10:00pm</slot>
        <name>…</name>
   </Time>
• Think generically
Ex. Don’t use <NBC>…</NBC> <ABC>…</ABC> to group different
   networks
Use <name>NBC</name><name>ABC</name>
• Think hierarchically
Start with a meaningful root element and work downward to successive
   levels of detail
            What is XSL?
• XSL is a language that allows one to
  describe for a browser how to process an
  XML file.
• XSL can convert an XML file into another
  format XML file.
• XSL can convert an XML file into a non-
  XML file.
                       XSL
• The most common type of XSL processing is to
  convert XML file into HTML file which can be
  displayed by browsers. We will focus on this use
  of XSL.
• XSL is the bridge between XML and HTML.
• We can use XSL to have different HTML formats
  of the same data represented in XML.
• Separating data (contents) from style tags (display
  commands).
• Example:

				
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