XML

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XML
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What is XML?

• The Extensible Markup Language (XML) is a
  general-purpose markup language.
• It is classified as an extensible language
  because it allows its users to define their own
  tags.
• XML is a markup language for documents containing
  structured information.
• Its primary purpose is to facilitate the sharing
  of structured data across different information
  systems, particularly via the Internet.
• XML is recommended by the World Wide Web
  Consortium. It is a fee-free open standard.

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So XML is Just Like HTML?

• No. In HTML, both the tag semantics and the tag
  set are fixed.
• An lth1gt is always a first level heading and the
  tag ltmscitgt is meaningless.
• XML specifies neither semantics nor a tag set.

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Why Is XML Important?

• Plain Text
• Since XML is not a binary format, you can create
  and edit files with anything from a standard text
  editor to a visual development environment.
• That makes it easy to debug your programs, and
  makes it useful for storing small amounts of
  data.
• XML provides scalability for anything from small
  configuration files to a company-wide data
  repository.
• Data Identification
• XML tells you what kind of data you have, not how
  to display it.

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Why Is XML Important?

• XML can Separate Data from HTML
• With XML, your data is stored outside your HTML.
• XML is Used to Exchange Data
• With XML, data can be exchanged between
  incompatible systems.
• XML and B2B
• With XML, financial information can be exchanged
  over the Internet.

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Why Is XML Important?

• XML Can be Used to Share Data
• With XML, plain text files can be used to share
  data.
• Since XML data is stored in plain text format,
  XML provides a software- and hardware-independent
  way of sharing data.
• In the real world, computer systems and databases
  contain data in incompatible formats. One of the
  most time-consuming challenges for developers has
  been to exchange data between such systems over
  the Internet.
• Converting the data to XML can greatly reduce
  this complexity and create data that can be read
  by many different types of applications.

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Why Is XML Important?

• XML Can Be Used to Create Specialized
  Vocabularies
• XML is an extensible standard.
• By using XML as a base, you can create your own
  vocabularies. Wireless Application Protocol
  (WAP), Wireless Markup Language (WML), and Simple
  Object Access Protocol (SOAP) are some examples
  of specialized XML vocabularies.

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Other Applications of XML

• Molecular sciences with CML
• Peter Murray-Rusts Chemical Markup Language
  (CML)
• Science and math with MathML
• The Mathematical Markup Language (MathML) is an
  XML application for mathematical equations.
• Webcasting with CDF
• Microsofts Channel Definition Format (CDF) is an
  XML application for defining channels. Web sites
  use channels to upload information to readers who
  subscribe to the site rather than waiting for
  them to come and get it. This is alternately
  called Webcasting or push.

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Other Applications of XML

• Software updates through OSD
• The Open Software Description (OSD) format is an
  XML application co-developed by Marimba and
  Microsoft for updating software automatically.
  OSD defines XML tags that describe software
  components. The description of a component
  includes the version of the component, its
  underlying structure, and its relationships to
  and dependencies on other components
• Vector graphics with both PGML and VML
• Vector graphics better than GIF, JPEG images
• The Precision Graphics Markup Language (PGML)
  from IBM, Adobe, Netscape, and Sun.
• The Vector Markup Language (VML) from Microsoft,
  Macromedia, Autodesk, Hewlett-Packard, and Visio

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Other Applications of XML

• Financial data with OFX
• the Open Financial Exchange Format (OFX) is an
  XML application used to describe financial data
  of the type youre likely to store in a personal
  finance product like Money or Quicken. Any
  program that understands OFX can read OFX data.
  And since OFX is fully documented and
  non-roprietary (unlike the binary formats of
  Money, Quicken, and other programs) its easy for
  programmers to write the code to understand OFX.

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Other Applications of XML

• Financial data with OFX

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Other Applications of XML

• Financial data with OFX

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Other Applications of XML

• Automated voice responses with VoxML
• Financial data with OFX
• Legally binding forms with XFDL
• Human resources job information with HRML
• Meta-data through RDF
• Internal use of XML by various companies,
  including Microsoft, Federal Express, and Netscape

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XML Syntax

• The syntax rules of XML are very simple and very
  strict.
• An Example XML Document
• XML documents use a self-describing and simple
  syntax.
• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• ltnotegt
• lttogtStudentslt/togt
• ltfromgtFacultylt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtLearn XMLlt/bodygt
• lt/notegt

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XML Syntax

• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• defines the XML version and the character
  encoding used in the document.
• In this case the document conforms to the 1.0
  specification of XML and uses the ISO-8859-1
  (Latin-1/West European) character set.
• ltnotegt
• The next line describes the root element of the
  document

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XML Syntax

• The next 4 lines describe 4 child elements of the
  root (to, from, heading, and body)
• lttogtStudentslt/togt
• ltfromgtFacultylt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtLearn XMLlt/bodygt
• lt/notegt
• last line defines the end of the root element

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XML Syntax

• All XML Elements Must Have a Closing Tag
• With XML, it is illegal to omit the closing tag.
• In HTML some elements do not have to have a
  closing tag.
• The following code is legal in HTML
• ltpgtThis is a paragraph
• ltpgtThis is another paragraph
• XML all elements must have a closing tag, like
  this
• ltpgtThis is a paragraphlt/pgt
• ltpgtThis is another paragraphlt/pgt

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XML Syntax

• XML Tags are Case Sensitive
• ltMessagegtThis is incorrectlt/messagegt
• ltmessagegtThis is correctlt/messagegt

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XML Syntax

• XML Elements Must be Properly Nested
• Improper nesting of tags makes no sense to XML.
• ltbgtltigtThis text is bold and italiclt/bgtlt/igt
• In XML all elements must be properly nested
  within each other like this
• ltbgtltigtThis text is bold and italiclt/igtlt/bgt

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XML Syntax

• XML Documents Must Have a Root Element
• All XML documents must contain a single tag pair
  to define a root element.
• All other elements must be within this root
  element.
• All elements can have sub elements (child
  elements). Sub elements must be correctly nested
  within their parent element
• ltrootgt
• ltchildgt
• ltsubchildgt.....lt/subchildgt
• lt/childgt
• lt/rootgt

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XML Syntax

• XML Attribute Values Must be Quoted
• With XML, it is illegal to omit quotation marks
  around attribute values. 
• XML elements can have attributes in name/value
  pairs just like in HTML.
• In XML the attribute value must always be quoted.
  
• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• ltnote date12/11/2002gt
• lttogtStudentslt/togt
• lt/notegt
• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• ltnote date"12/11/2002"gt
• lttogtStudentslt/togt
• lt/notegt

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XML Syntax

• With XML, White Space is Preserved
• With XML, the white space in your document is not
  truncated.
• Comments in XML
• The syntax for writing comments in XML is similar
  to that of HTML.
• lt!-- This is a comment --gt

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XML Sibling Elements

• ltbookgt
• lttitlegtMy First XMLlt/titlegt
• ltprod id"33-657" edia"paper"gtlt/prodgt
• ltchaptergtIntroduction to XML
• ltparagtWhat is HTMLlt/paragt
• ltparagtWhat is XMLlt/paragt
• lt/chaptergt
• ltchaptergtXML Syntax
• ltparagtElements must have a closing taglt/paragt
• ltparagtElements must be properly nestedlt/paragt
• lt/chaptergt
• lt/bookgt
• Sibling Elements Title, prod, and chapter are
  siblings
• (or sister elements) because they have the same
  parent.

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Use of Elements vs. Attributes

• Data can be stored in child elements or in
  attributes.
• ltperson gender"female"gt
• ltfirstnamegtABClt/firstnamegt
• ltlastnamegtXYZlt/lastnamegt
• lt/persongt
• ltpersongt
• ltgendergtfemalelt/gendergt
• ltfirstnamegtABClt/firstnamegt
• ltlastnamegtXYZlt/lastnamegt
• lt/persongt

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Use of Elements vs. Attributes

• Some of the problems with using attributes are
• attributes cannot contain multiple values (child
  elements can)
• attributes are not easily expandable (for future
  changes)
• attributes cannot describe structures (child
  elements can)
• attributes are more difficult to manipulate by
  program code
• attribute values are not easy to test against a
  Document Type Definition (DTD) - which is used to
  define the legal elements of an XML document

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Well Formed XML Document

• Well Formed XML Documents
• A "Well Formed" XML document has correct XML
  syntax.
• A "Well Formed" XML document is a document that
  conforms to the following
• XML documents must have a root element
• XML elements must have a closing tag
• XML tags are case sensitive
• XML elements must be properly nested
• XML attribute values must always be quoted

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Why usa a DTD?

• With a DTD, each of your XML files can carry a
  description of its own format.
• With a DTD, independent groups of people can
  agree to use a standard DTD for interchanging
  data.
• Your application can use a standard DTD to verify
  that the data you receive from the outside world
  is valid.
• You can also use a DTD to verify your own data.

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Valid XML

• Valid XML Documents
• A "Valid" XML document also conforms to a DTD.
• A "Valid" XML document is a "Well Formed" XML
  document, which also conforms to the rules of a
  Document Type Definition (DTD)

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Valid XML

• XML DTD
• This is a statement of rules for an XML document
• The purpose of a DTD is to define the legal
  building blocks of an XML document.
• It helps ensure the accuracy of the information
  you collect.
• It helps ensure that the information gathered is
  in the most usable format for your business needs.

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DTD

• A DTD can be declared inline inside an XML
  document, or as an external reference.
• Internal DTD Declaration
• If the DTD is declared inside the XML file, it
  should be wrapped in a DOCTYPE definition with
  the following syntax
• lt!DOCTYPE root-element element-declarationsgt

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DTD Terms
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Inline to DTD

• lt?xml version"1.0"?gt
• lt!DOCTYPE note
• lt!ELEMENT note (to,from,heading,body)gt
• lt!ELEMENT to (PCDATA)gt
• lt!ELEMENT from (PCDATA)gt
• lt!ELEMENT heading (PCDATA)gt
• lt!ELEMENT body (PCDATA)gt gt
• ltnotegt
• lttogtStudentslt/togt
• ltfromgtFacultylt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget to learn XML !!!lt/bodygt
• lt/notegt

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External DTD Declaration

• If the DTD is declared in an external file, it
  should be wrapped in a DOCTYPE definition with
  the following syntax
• lt!DOCTYPE root-element SYSTEM "filename"gt
• lt?xml version"1.0"?gt
• lt!DOCTYPE note SYSTEM "note.dtd"gt
• ltnotegt
• File "note.dtd" which contains the DTD
• lt!ELEMENT note (to,from,heading,body)gt
• lt!ELEMENT to (PCDATA)gt
• lt!ELEMENT from (PCDATA)gt
• lt!ELEMENT heading (PCDATA)gt
• lt!ELEMENT body (PCDATA)gt

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DTD Explanation

• !DOCTYPE note defines that the root element of
  this document is note
• !ELEMENT note defines that the note element
  contains four elements "to,from,heading,body
• !ELEMENT to defines the to element to be of type
  "PCDATA"
• !ELEMENT from defines the from element to be of
  type "PCDATA"
• !ELEMENT heading defines the heading element to
  be of type "PCDATA"
• !ELEMENT body defines the body element to be of
  type "PCDATA"

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DTD Elements

• DTD elements can be defined as follows
• lt!ELEMENT Name EMPTYgt
• Sometimes, you may want an element type to remain
  empty with no content to call its own
• lt!ELEMENT Name ANYgt
• If you want your element to serve as a catch-all
  box that you can put anything in, you may want to
  use another type of content specification ANY.
• If you declare an element to contain ANY content,
  you allow that element type to hold any element
  or character data.

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Element Attribute

• lt!ATTLIST element-name attribute-name datatype
  defaultvaluegt
• The attribute-list declaration begins with the
  !ATTLIST string, followed by white space.
• Next is the element name, the associated
  attributes name, its type, and a default value.
• For Example
• lt!ATTLIST customer custType CDATA REQUIREDgt
• lt!ATTLIST price priceType (Retail Wholesale)
  REQUIREDgt

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Element Attribute

• REQUIRED means you must always include the
  attribute when the element is used.
• No specific default value for the attribute can
  be included in this case, so you must include a
  value for it in your
• lt!ATTLIST element-name attribute-name CDATA
  REQUIREDgt
• IMPLIED means the attribute is optional. The
  attribute may be used in an element, but no
  default value is provided if the attribute isnt
  used.
• lt!ATTLIST element-name attribute-name CDATA
  IMPLIEDgt

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Element Attribute

• FIXED means the attribute is optional, but if
  used, the attribute must always take on the
  default value assigned in the DTD.
• lt!ATTLIST element-name attribute-name FIXED
  valuegt

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Element and its attribute example
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DTD PCDATA

• PCDATA means parsed character data.
• Think of character data as the text found between
  the start tag and the end tag of an XML element.
• PCDATA is text that WILL be parsed by a parser.

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DTD CDATA

• CDATA means character data.
• CDATA is text that will NOT be parsed by a
  parser.
• Tags inside the text will NOT be treated as
  markup and entities will not be expanded.

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XML Schema

• XML Schema is an XML-based alternative to DTDs.
• An XML Schema describes the structure of an XML
  document.
• The XML Schema language is also referred to as
  XML Schema Definition (XSD).

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An XML Schema

• The purpose of an XML Schema is to define the
  legal building
• blocks of an XML document, just like a DTD.
• defines elements that can appear in a document
• defines attributes that can appear in a document
• defines which elements are child elements
• defines the order of child elements
• defines the number of child elements
• defines whether an element is empty or can
  include text
• defines data types for elements and attributes
• defines default and fixed values for elements and
  attributes

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XML Schema

• XML Schemas use XML Syntax
• You don't have to learn a new language
• You can use your XML editor to edit your Schema
  files
• You can use your XML parser to parse your Schema
  files
• You can manipulate your Schema with the XML DOM

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XML Schema Example

• The following example is an XML Schema file
  called "note.xsd" that defines the elements of
  the XML document ("note.xml")
• ltxselement name"note"gt
• ltxscomplexTypegt
• ltxssequencegt
• ltxselement name"to" type"xsstring"/gt
• ltxselement name"from" type"xsstring"/gt
• ltxselement name"heading" type"xsstring"/gt
  ltxselement name"body" type"xsstring"/gt
• lt/xssequencegt
• lt/xscomplexTypegt
• lt/xselementgt

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XML Schema

• The note element is a complex type because it
  contains other elements.
• The other elements (to, from, heading, body) are
  simple types because they do not contain other
  elements.

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XML Schema

• Simple element is an XML element that contains
  only text. It cannot contain any other elements
  or attributes.
• The text can be of many different types. It can
  be one of the types included in the XML Schema
  definition (boolean, string, date, etc.), or it
  can be a custom type that you can define
  yourself.
• You can also add restrictions (facets) to a data
  type in order to limit its content, or you can
  require the data to match a specific pattern.

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XML Schema

• The syntax for defining a simple element is
• ltxselement nameabc" typexyz"/gt
• Where abc is the name of the element and xyz is
  the data type of the element.
• XML Schema has a lot of built-in data types. The
  most common types are
• xsstring
• xsdecimal
• xsinteger
• xsboolean
• xsdate
• xstime

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XML Schema

• Here are some simple XML elements
• ltlastnamegtRajlt/lastnamegt
• ltagegt36lt/agegt
• ltdateborngt1987-03-27lt/dateborngt
• Here are the corresponding simple element
  definitions
• ltxselement name"lastname" type"xsstring"/gt
• ltxselement name"age" type"xsinteger"/gt
• ltxselement name"dateborn" type"xsdate"/gt

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XML Schema

• Simple elements may have a default value OR a
  fixed value specified.
• Default value is automatically assigned to the
  element when no other value is specified. In the
  following example the default value is "red"
• ltxselement name"color" type"xsstring
  default"red"/gt
• Fixed value is also automatically assigned to the
  element, and you cannot specify another value.
  In the following example the fixed value is
  "red"
• ltxselement name"color" type"xsstring"
  fixed"red"/gt

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XML Schema

• The syntax for defining an attribute is
• ltxsattribute nameabc" typexyz"/gt
• Where abc is the name of the attribute and xyz
  specifies the data type of the attribute.
• Simple elements cant have attributes!

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XML Schema

• When an XML element or attribute has a data type
  defined, it puts restrictions on the element's or
  attribute's content.
• If an XML element is of type "xsdate" and
  contains a string like "Hello World", the element
  will not validate.
• With XML Schemas, you can also add your own
  restrictions to your XML elements and attributes.

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XML Schema

• The following example defines an element called
  "age" with a restriction. The value of age cannot
  be lower than 0 or greater than 120
• ltxselement name"age"gt
• ltxssimpleTypegt
• ltxsrestriction base"xsinteger"gt
• ltxsminInclusive value"0"/gt
• ltxsmaxInclusive value"120"/gt
• lt/xsrestrictiongt
• lt/xssimpleTypegt
• lt/xselementgt

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XML Schema

• The example below defines an element called "car"
  with a restriction. The only acceptable values
  are Audi, Ford, BMW
• ltxselement name"car" type"carType"/gt
• ltxssimpleType name"carType"gt
• ltxsrestriction base"xsstring"gt
• ltxsenumeration value"Audi"/gt
• ltxsenumeration valueFord"/gt
• ltxsenumeration value"BMW"/gt
• lt/xsrestrictiongt
• lt/xssimpleTypegt
• Note In this case the type "carType" can be used
  by other elements because it is not a part of the
  "car" element.

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An XML Document