Web EngineeringAdvanced Web Engineering

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Web Engineering/Advanced Web Engineering

• Week 11 - XML (Extensible Markup Language)

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Introduction

• XML
• The Extensible Markup Language (XML) is a
  document processing standard proposed by the
  World Wide Web Consortium (W3C), which is related
  to Standard Generalised Markup Language (SGML).
• Possible to search, sort, manipulate and render
  XML using Extensible Markup Language (XSL)
• Highly portable
• Files end in the .xml extension

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From HTML to XML..

• HTML major drawback information loses its
  structure when translated into HTML
• HTML is a presentation-oriented markup language,
  so information embodied in it is difficult to
  process
• Information and knowledge servers are overloaded
  because have to search information and perform
  format processing
• Servers often answer the same request many times
  if users request several views on the same data

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From HTML to XML..

• HTML
• Lacks extensibility cant create tags or
  attributes to parameterise or semantically
  qualify data
• Lacks structure does not support the
  specification of deep structures needed to
  represent database schemas or object-oriented
  hierarchies
• Lacks validation does not support language
  specification that lets applications check
  imported datas structural validity

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XML..

• XML is not for displaying information but for
  managing information.
• Working group of World Wide Web Consortium (W3C)
  created XML as a standard for creating markup
  languages.
• Designed it for distributing structured
  documents over the web
• A kind of light SGML (Standard General Markup
  Language) simplified to meet Web requirements
• Unlike HTML, XML lets users
• Extract data from a document
• Define their own tags and attributes
• Define data structures and nest document
  strcutures to any complexity level
• Make applications that validate a documents
  structure. Any XML document can contain an
  optional description of its grammar for use by
  applications that perform structural validation

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XML..

• The problem that XML helps us to solve is how to
  transfer data between servers, or between the
  client and the server.
• Transferring data using a binary format is
  complicated, as problems arise because different
  platforms tend not to represent or order data the
  same way.
• Therefore XML, a standardised text format,
  becomes an attractive alternative.

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XML..

• It is a Markup language for describing structured
  data content is separated from presentation
• XML documents contain only data
• Applications decide how to display the data
• Language for creating markup languages
• Can create new tags
• XML documents contain only data, not formatting
  instructions, so applications that process XML
  documents must decide how to display the
  documents data.
• For example a PDA (personal digital assistant)
  may render an XML document differently than a
  wireless phone or desktop computer would render
  that document.

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XML..

• XML is a meta-language
• With HTML, existing markup is static ltHEADgt and
  ltBODYgt for example, are tightly integrated into
  the HTML standard and cannot be changed or
  extended.
• XML, on the other hand, allows ou to create your
  own markup tags and configure each to your
  liking for example
• ltWebEngHeadinggt
• ltWebEngSummarygt
• ltWebEngReallyWildFontgt
• Each of these elements can be defined through
  user defined document type definitions (DTD) and
  stylesheets and applied to one or more XML
  documents.
• There are no correct tags for an XML document,
  except those defined by the author

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XML applications

• XML permits document authors to create markup for
  virtually any type of information.
• Authors can create entirely new markup languages
  for describing specific types of data, including
  mathematical formulas, chemical molecular
  structures, music, recipes etc.
• XHTML
• VoiceXML (for speech)
• MathML (for mathematics)
• SMIL (the Synchronous Multimedia Integration
  Language, for multimedia presentations)
• CML (Chemical Markup Language, for chemistry)
• XBRL (Extensible Business Reporting Language, for
  financial data exchange)

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DTD valid wellformed

• An XML document optionally can reference a
  document that defines that XML documents
  structure. This document is either a Document
  Type Definition (DTD) or a schema.
• A DTD (document type definition) is a syntactic
  specification used as a model for XML documents.
• It contains definitions of the elements and their
  attached attributes.
• When an XML document references a DTD or schema,
  some parsers (called validating parsers) can read
  the DTD/schema and check that the XML document
  follows the structure that the DTD/schema
  defines.
• If it conforms to the DTD/schema it is valid.
• If the parser can process an XML document
  successfully it is well-formed (syntactically
  correct).
• By definition, a valid document is well-formed.

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XML Parsers

• Processing an XML document requires a software
  program called an XML parser (or processer).
  These are available at no charge in many
  languages (Java, Python, C etc.).
•  
• www.xml.com/xml/pub/Guide/XML_Parsers
• Parsers check an XML documents syntax and enable
  software programs to process marked-up data. XML
  parsers can support the Document Object Model
  (DOM) or the Simple API for XML (SAX).
• DOM Build a tree structure containing the XML
  documents data
• SAX Process the document and generate events

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Structuring Data

• Element types
• Can be declared to describe data structure
• XML elements
• Root element
• Must be exactly one per XML document
• Contains all other elements in document
• Lines preceding the root element are called the
  prolog
• Container element
• Contains sub-elements (children)
• Empty element
• No matching end tag
• In HTML, IMG
• Terminate with forward slash (/)

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Example 1

• Declaration of XML version

Outside DTD needed webengxml.dtd SYSTEM keyword
lt?xml version"1.0" standalone"no"?gt lt!DOCTYPE
WebEngModules SYSTEM webengxml.dtdgt lt!
comment any text --!gt lt WebEngModules
xmlnsWebEnghttp//www.webeng.ac.uk/gt lt
WebEngTitlegtXML Lecturelt/ WebEngTitlegt lt
WebEngSummarygtAll about XMLlt/ WebEngSummarygt lt
WebEngHoursgt2lt/ WebEng Hours gt lt
/WebEngModulesgt
Root element outermost element in document
denotes start and end points
Descendants of ltWebEngModulesgt element
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Extensible Style Language (XSL)

• xmlns
• Defines an XML namespace
• Identifies collections of element type
  declarations so that they do not conflict with
  declarations of same name created by other
  programmers
• Predefined namespaces
• xml, xsl
• Programmers can create own namespaces
• ltTitlegtXML Lecturelt/Titlegt
• ltTitlegtCGI Lecturelt/Titlegt
• Can be differentiated by using namespaces
• ltWebEngTitlegtXML Lecturelt/WebEngTitlegt
• ltObjectDevTitlegtInheritance Lecturelt/ObjectDevTi
  tlegt

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Example 2 XML file
lt?xml version "1.0"?gt lt! Web Eng letter
formatted with XML --gt lt!DOCTYPE letter SYSTEM
walter.dtd"gt ltlettergt ltcontact type
"from"gt ltnamegtWalter Enginelt/namegt ltaddress1gt23
Harley St.lt/address1gt ltaddress2gtlt/address2gt ltcit
ygtSunderlandlt/citygt ltpostcodegtWE6
0DDlt/postcodegt ltflag gender "M"/gt lt/contactgt lt
contact type "to"gt ltnamegtT. Blairlt/namegt ltaddr
ess1gt10 Downing St.lt/address1gt ltaddress2gtNice
Arealt/address2gt ltcitygtLondonlt/citygt
ltpostcodegtlt/postcodegt ltflag gender
"M"/gt lt/contactgt ltsalutationgtDear
Sirlt/salutationgt ltparagraphgtWe would be very
happy to teach about Web Engineering.lt/paragraphgt
ltclosinggtAll yourslt/closinggt ltsignaturegtMr.
Enginelt/signaturegt lt/lettergt
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Document Type Definitions (DTD)

• Document Type Definition
• Specify list of element types, attributes and
  their relationships to each other
• Optional, but recommended for program conformity
• !Element
• Element type declaration defines the rules for
  an element
• Plus sign () one or more occurrences
• Asterisk () any number of occurrences
• Question mark (?) either zero or exactly one
  occurrence
• Omitted operator exactly one occurrence
• PCDATA
• The element can store parsed character data

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Document Type Definitions (DTD)

• !ATTLIST
• Defines attributes for an element
• IMPLIED
• Can assign its own type attribute or ignore
• REQUIRED
• The specified attribute must be declared in the
  document
• FIXED
• The Specified attribute must be declared with
  given value

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Example 3 DTD file
lt!-- walter.dtd --gt lt!ELEMENT letter (contact,
salutation, paragraph, closing, signature
)gt lt!ELEMENT contact (name, address1, address2,
city, postcode, gender)gt lt!ATTLIST contact
type CDATA IMPLIEDgt lt!ELEMENT name
(PCDATA)gt lt!ELEMENT address1 (PCDATA)gt lt!ELEMENT
address2 (PCDATA)gt lt!ELEMENT city
(PCDATA)gt lt!ELEMENT postcode (PCDATA)gt lt!ATTLIST
flag gender (M F) "M"gt

• walter.dtd
• Declare elements and elements attributes
• IMPLIED indicates attribute is
  unspecifiedsystem gives it a value
• CDATA states that attribute contains a string
• PCDATA specifies parsed character data
• EMPTY specifies element does not contain content
  (commonly used for attributes)

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Example 3 IE display
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Customized Markup Languages

• Customized Markup Languages
• Can create own tags to describe data, creating a
  new markup language
• MathML
• Wireless Markup Language (WML)
• Extensible Business Reporting Language (XBRL)
• Electronic Business XML (ebXML)
• Financial Products Markup Language (FpML)

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MathML

• MathML
• Developed by W3C for describing mathematical
  notations and expressions
• Amaya browser
• www.w3.org/Amaya/User/BinDist.html

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WML

• Wireless Markup Language
• Allows portions of Web pages to be displayed on
  wireless devices
• Works with Wireless Application Protocol (WAP)
• www.wapforum.org
• www.xml.com/pub/Guide/WML

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XBRL

• Extensible Business Reporting Language (XBRL)
• Facilitates the creation, exchange and validation
  of financial information
• Namespaces
• Minimize conflicts between XML elements with the
  same name
• Example
• ltschoolsubjectgtEnglishlt/schoolsubjectgt
• ltmedicalsubjectgtThrombosislt/medicalsubjectgt

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ebXML

• Electronic Business XML (ebXML)
• Used for exchanging business data
• www.ebxml.org

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FpML

• Financial Products Markup Language (FpML)
• Emerging standard for exchanging financial
  information over the Internet
• www.fpml.org

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Other Markup Languages

• Chemical Markup Language (CML) www.xml-cml.org
• VoiceXML www.voicexml.org
• Synchronous Multimedia Integration Language (SMIL
  ) www.w3.org/AudioVideo
• Vector Markup Language (VML) www.w3.org/TR/NOTE-
  VML
• Product Data Markup Language (PDML)
  www.pdml.org
• Commerce XML (cXML) www.cxml.org/home
• XMI (XML Metadata Interchange) www.omg.org
• Trading Partner Agreement Markup Language (tpaML)
• www-4.ibm.com/software/developer/library/tpaml.
  html
• Small to Medium Business XML (SMBXML)
  www.smbxml.org
• Financial XML (FinXML) www.finxml.org
• Financial Information Exchange Markup Language
  (FixML)
• www.fixprotocol.org

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Using XML with HTML

• XML documents are data sources
• XML documents embedded in HTML documents
• Using the XML tag
• Embedded XML document called a data island
• ltXML ID xmldocgtlt/XMLgt
• Marks boundaries of data island
• Attribute ID
• Name used to reference the data island
• DATASRCname attribute
• In opening TABLE elements start-tag, binds
  specified data island to table
• To use bound bound data
• Use SPAN element with a DATAFLD attribute

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Document Object Model (DOM)

• Document Object Model (DOM)
• Retrieving data from a text file impractical
• DOM created when XML file is parsed
• Hierarchical tree structure
• Node Each name in the tree structure
• Single root node contains all other nodes
• Tree structure for article.xml

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Document Object Model (DOM)
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Extensible Style Language (XSL)

• XML documents can be placed in their own file
• Referenced in HTML document
• ltXML ID name SRC fileName.htmlgtlt/XMLgt
• xslfor-each element
• Iterates over items in specified document

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Microsoft Schema

• Schema
• Microsofts expansion of the DTD
• Called XML-Data
• Developed to a schema create document definitions
  using XML syntax
• Schemas or DTDs
• May be used to specify documents grammar
• DTDs may be preferred because Microsofts schema
  language is proprietary technology

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Extensible Hypertext Markup Language (XHTML)

• XHTML
• Allows
• Complex documents to be created by combining HTML
  elements with XMLs extensibility
• Ability to create new elements
• Example XHTML document might combine HTML
  elements with MathML and CML elements
• Well formed documents
• Each XHTML document validated using DTDs
• Features provide structure HTML lacks
• Uses XML syntax
• All tags lowercase and closed

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Validation of xhtmlExample.html
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Microsoft BizTalk

• Internet data exchange
• Sending data between organizations is difficult
• Different platforms, applications and data
  specifications
• XML simplifies data transfers
• Microsoft BizTalk
• Manages and facilitates business transactions
• Ensures uniformity
• Three parts
• BizTalk Server
• BizTalk Framework
• BizTalk Schema Library

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Simple Object Access Protocol (SOAP)

• Data transfers
• Clients little processing power, invoke method
  calls on other machines
• Behind firewalls
• SOAP messages
• Envelope structure for describing a method call
• Request remote procedure call
• Response HTTP response containing results of
  method call