SASIntrNet V8

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The EXtensible Markup Language

Mary C. Parmelee
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What is XML?

• XML is a text-based meta-language that was
  designed to
• structure and describe Web data and make it more
  human readable
• be completely customizable and self describing
• be platform independent for seamless
  interoperability
• Facilitate the translation of a document from one
  language to another

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Why is XML Important?

• Two main reasons
• Data interchange allows data to be shared
  between different applications and systems
• Flexibility allows data to be centrally stored
  and transformed into different medias and formats
  such as HTML

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Evolution of XML

• First there was Standard Generalized Markup
  Language (SGML)
• provides a specification for the writing of
  markup languages
• Developed by IBM researchers in 1965
• Became an ISO standard in 1986
• Powerful but complex

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Evolution of XML

• Then there was Hypertext Markup Language (HTML)
• 1989 researcher Tim Berners-Lee proposed a simple
  system to share documents using hyperlinks
• Named the hypertext system the WWW
• Defined a simple SGML Document Type (HTML)
• World Wide Web Consortium W3C founded in 1992 to
  standardize HTML

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Evolution of XML

• Finally eXtensible Markup Language (XML)
• HTML was
• Portable
• Easy to understand and use
• BUT
• Fixed set of tags-not extensible
• Designed to format and display data not describe
  its content
• Does not address the transfer platform
  independent transfer of data
• 1996 W3C began XML development
• released XML 1.0 spec in 1998

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The XML Family

• 1998 CSS Cascading Style Sheets
• 2000 XSL Extensible Style Language
• 2000 XLL (XLINK) XML Linking Language
• 2000 XPointer XML Pointing Language
• 1999 XML Namespaces
• 1999 XML Schema
• 2000 XForms
• XML Query

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How Does XML Differ from HTML?

• Two main differences
• Both derived from the SGML standard BUT
• HTML is an application of SGML called a Document
  Type Definition (DTD) that specifies Markup
• XML is a subset of SGML allows specification of
  custom DTDs and associated Markup
• HTML specifies presentation
• XML specifies data structure (content)

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What Does XML Look Like?

• Sample Data

Title
Author
Price
Introduction to XML
Mark Torr
22.00
Advanced XML
Mark Torr
32.00
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What Does XML Look Like?
Notice that there are NO presentation tags. XML
simply defines a data structure
lt?xml version1.0?gt ltbooksgt ltbook
nameIntroduction to XML price22.00gt
ltauthorgtMark Torrlt/authorgt lt/bookgt
ltbook nameAdvanced XML price32.00gt
ltauthorgtMark Torrlt/authorgt
lt/bookgt lt/booksgt
It is pretty self describing. It is clear we are
talking about books and that the data related to
that book from simply reading the tags.
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XML Structure Declaration

• XML declarations normally look as shown below
• lt?xml version1.0?gt
• You can tell this is a declaration by the ? That
  follows immediately after the opening lt and the
  ? immediately prior to the closing gt.
• XML declarations, otherwise known as processing
  instructions, are used by parsers.

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XML Structure Document Root

• Every XML document must contain a document root
  eg ltbooksgtlt/booksgt
• The document root is simply the element that
  appears first after the processing instruction.
• A document root cannot be empty.

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XML Structure Element

• An XML element defines the content of an XML
  document eg ltbooksgtlt/booksgt
• Elements can contain
• Other Elements
• Text
• Known as PCDATA (Parsable character data)
• Nothing

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XML Structure Attribute

• An XML attribute adds data about the elements.
• Attributes can be considered similar to fields in
  a database.

ltbook nameIntroduction to XML
price22.00gt lt/bookgt
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XML Structure Entities

• Here is a list of predefined entities. There are
  only five and so it is pretty easy to remember
  them.

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XML Structure Example
Attribute. Attributes always appear with within
Elements as shown in this example. Here name is
an attribute of the element book and price is
also an attribute of the element book.
Declaration or processing instruction. Used by
Parsers or XML editing tools.
lt?xml version1.0?gt ltbooksgt ltbook
nameIntroduction to XML price22.00gt
ltauthorgt Mark Torr lt/authorgt lt/bookgt
ltbook nameAdvanced XML price32.00gt
ltauthorgt Mark Torr amp His
Friendlt/authorgt lt/bookgt lt/booksgt
lt?xml version1.0?gt ltbooksgt ltbook
nameIntroduction to XML price22.00gt
ltauthorgtMark Torrlt/authorgt lt/bookgt
ltbook nameAdvanced XML price32.00gt
ltauthorgtMark Torr amp His Friendlt/authorgt
lt/bookgt lt/booksgt
Document root
Element. Other valid elements in this XML
document are ltbookgt, ltauthorgt. Notice that all
Elements start with a lt and end with a gt
Entity. This is the only entity in this XML
document. Entities always start with an and
end with a
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What is Well Formed XML?

• A well formed XML document must conform to these
  rules
• All element tags have been closed
• All attribute values are enclosed in quotes
• Nesting of components is correct
• Element tags are of the same case.

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Lets Try Coding In XML
lt?xml version1.0?gt ltbooksgt ltbook
nameIntroduction to XML price22.00gt
ltauthorgt Mark Torr lt/authorgt
ltpersonal age22/gt lt/bookgt ltbook
nameAdvanced XML price32.00gt
ltauthorgt Mark Torr amp His Friendlt/authorgt
ltpublishergt Harry Smiths lt/publishergt
lt/bookgt lt/booksgt
Save it into your Ctemp file as sample.xml
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Load this into IE5

• IE has parser that will tell you if your XML is
  Well Formed
• Find the the Ctemp directory
• Find your file named sample.xml
• It will have an icon like this
• Double click on the file to open in Internet
  Explorer

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Congratulations! o)
If your syntax is correct, the screen looks like
this
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Uh Oh! o(
If the screen looks like this, you made an error
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Apply the Rules One At A Time

• A well formed XML document must conform to these
  rules
• All element tags have been closed
• All attribute values are enclosed in quotes
• Nesting of components is correct
• Element tags are of the same case.

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What next?

• Once you have a well formed document then you are
  able to start to use things such as the DOM
  (Document Object Model), XSL (EXtensible Style
  Language) to transform this into another markup
• HTML
• XML (You can subset and combine XML documents
  documents to create new XML documents.)

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What next?

• Once a document is well formed you can also check
  if it is valid. A badly formed XML document is
  always invalid.
• To check if an XML document is valid you need to
  make use of DTDs.
• DTDs

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What is a DTD

• DTD stands for Document Type Definition
• Used to validate XML documents
• Defines a set of rules that the content of one or
  more XML files must adhere to in order for the
  document to be valid

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What is validation?

• Validation is the process of checking
• Data is in the proper order
• Data is in the proper format
• Data is the correct type
• Any mandatory fields are present

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Book Example DTD
lt!ELEMENT books (book)gt lt!ELEMENT book ( title,
author , price, publisher)gt lt!ELEMENT title
(PCDATA)gt lt!ELEMENT author (PCDATA)gt lt!ELEMENT
price (PCDATA)gt lt!ELEMENT address
(PCDATA)gt lt!ELEMENT publisher (PCDATA)gt lt!ATTLI
ST book Edition CDATA REQUIREDgt lt!ATTLIST
publisher Address CDATA IMPLIEDgt lt!ATTLIST price
Currency (Dollar Pound Yen) "Pound"gt
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Conclusion

• XML is used to define the structure of the data.
• XML does not define any aspect of presentation.
• XML has strict rules that must be adhered to
  unlike HTML which is a little more forgiving.
• Making an XML document well formed is the first
  step towards either doing transformation or
  ensuring it is a valid XML document.
• IE5 can be used to root out anything that is
  making an XML document badly formed provided you
  give the file a .xml extension.

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Further reading

• Extensible Markup Language (XML) 1.0
• http//www.w3.org/TR/WD-xml
• Defines the syntax of XML.