Section 1 Internet Overview

1
WHAT THE HELL IS XML?
2
What the hell is XML?

• Markup Language
• Derived from SGML (Standardized General Markup
  Language)
• Describes the CONTENT (stylesheet has to be
  applied to format content)
• Structured documents, can be used like a database
  that you can send to your clients/suppliers
• They can then use the data in any XML-supporting
  database/app

3
Like HTML?

• Both based on SGML
• Both use tags lt gt
• In both, tags enclose content..
• ltTAGNAMEgt..content..lt/TAGNAMEgt
• In both, tags have attributes..
• ltTAGNAME ATTRIBUTENAMEattributevaluegt

4
Like HTML?

• XML MUST have closing tags
• ltPgtThis is a paragraph
• ltPgtThis is invalid in XML
• MUST have quotation marks around attributes
• ltFONT SIZE9gtNo quoteslt/FONTgt
• CaSE senSiTivE!
• ltCaSEgtThis will not closelt/CASEgt
• XML has a strict syntax
• Documents must be well-formed!
• XML documents must start with an xml tag..
• lt?xml version1.0 standaloneyes ?gt

5
Object Modelling

• ltAPOGEEgt
• ltEMPLOYEEgt
• ltNAMEgtIrfanlt/NAMEgt
• ltPHONEgt770-980-0099lt/PHONEgt
• lt/EMPLOYEEgt
• ltEMPLOYEEgt
• ltNAMEgtMichellelt/NAMEgt
• ltPHONEgt678-357-3661lt/PHONEgt
• lt/EMPLOYEEgt
• lt/APOGEEgt
• In a database, Apogee would be the database name,
  Employee would be the Table, Name and Phone would
  be columns
• In object models, Employee would be the object,
  Name and Phone would be Properties

6
Attributes

• ltAPOGEEgt
• ltEMPLOYEE roleprogrammergt
• ltNAMEgtIrfanlt/NAMEgt
• ltPHONE typehomegt678-981-0193lt/PHONEgt
• ltPHONE typecellgt770-980-0099lt/PHONEgt
• lt/EMPLOYEEgt
• ltEMPLOYEE roledirectorgt
• ltNAMEgtJoellt/NAMEgt
• ltPHONE typecellgt678-357-3661lt/PHONEgt
• lt/EMPLOYEEgt
• lt/APOGEEgt
• Debate over when to use attributes and when to
  use elements
• MS XML tends to use attributes by default (faster
  to process?)
• Standard XML used elements more

7
XML The Rules

• Document Type Definitions (DTDs)
• Give the rules for validating documents
• A bit like a database schema/object model
• Describes the rules of the structure
• Relationships between elements (e.g. one to many)
• Which elements contain which other elements
• In Backus Naur Form (BNF) obscure?
• XML Schemas
• For a similar purpose to DTDs
• Are taking over from DTDs
• Are expressed in XML
• ltxsdschemagtlt/xsdschemagt

8
XML The Rules

• Referencing a DTD
• lt!DOCTYPE DOCUMENT PUBLIC -//W3C//DTD HTML
  4.0//EN http//www.w3.org/TR/REC-html/strict.dtd
  gt
• The above is the strict DTD for DHTML (HTML 4)

9
XML Editors

• Schema Editors
• Some allow you to turn a DTD into a schema
• XML Spy
• Turbo XML
• Schema Verifiers
• Only check the doc is well formed
• Expat http//www.jclark.com/xml/expat.html
• Schema Validator
• World Wide Web Consortium
• http//www.w3.org/2000/09/webdata/xsv
• XML Parser
• Xerces Java
• http//xml.apache.org/xerces-j/