LIS1510 Library and Archives Automation Issues XML and extensible systems

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LIS1510 Library and Archives Automation Issues
XML and extensible systems

• Andy Dawson
• School of Library, Archive Information Studies,
  UCL (University of Malta 2008)

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What we will be covering today

• Shortcomings of HTML
• Generalised markup languages
• How XML works
• XML document types
• Other related extensible technologies

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Limitations of (X)HTML

• Fixed tag set (specifications determined by W3C)
• Intended for display of documents on the Web
• Doesnt do everything everyone wants
• Not easy to use for other purposes
• searching in documents
• analysis of documents

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Principles of Generalized Markup

• Descriptive markup encodes features within a
  document
• Say what those features are - not what to do with
  them
• Need to define your own tags
• Creates machine-independent data
• Data can then be used for different purposes

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SGML

• SGML Standard Generalized Markup Language
• International standard in 1986
• Metalanguage (syntactic framework) for defining
  markup tags
• Parts of SGML are rather complex
• Used by large projects
• Not particularly easy to get started

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XML

• XML (Extensible Markup Language)
• Adopted by World Wide Web Consortium in 1998
• Cut-down version of SGML
• Based on same principles
• Designed to implement easily on the Web

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Advantages of XML

• Machine-independent plain ASCII files
• Potential longevity
• Multi-purpose use
• Ability to analyse/manipulate content
• BUT need to define tag set!
• Not a replacement for HTML unless
  analysis/manipulation of data is required
• However, XHTML has become a reliable
  alternative option for simple web publishing

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Defining Your Own Tags

• Need to undertake document analysis
• Identify key features in document
• Identify structure of document
• Choose names for tags
• Only then can we apply the tag scheme

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Example of a Newspaper

• Name of newspaper
• Issue
• Article
• Headline
• Author
• Paragraphs
• Pictures

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Basics of XML Syntax

• Documents are composed of elements
• Start and end tags for every element - unlike
  HTML, end tags must be present
• also Empty elements
• Attributes
• modify an element
• have a name and a value
• Value must be enclosed in matching quotes (single
  or double)
• An element may have several attributes
• Documents can be Well-formed or Valid

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Well-formed Documents

• Well-formed documents follow XML syntax i.e.
• start and end tags
• attributes in quotes
• nested structure
• But they have no pre-defined structure!
• Therefore
• Can only check the syntax
• Cannot validate the structure of well-formed
  documents
• Prepares documents for potential use/conversion

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Valid Documents

• A Valid XML document contains (or refers to) a
  Document Type Definition (DTD)
• The DTD is a specification of the document
  structure identifying
• which elements are allowed
• where they are allowed
• which attributes they may take

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Related technologies

• CSS Cascading Style Sheets
• As used with HTML
• Concentrate only on appearance
• XHTML
• Version of HTML conformant with XML syntax
• XSL - eXtensible Stylesheet Language
• XML language for style sheets
• Controls the appearance of the elements within
  the document defines templates for processing
  elements
• XML Schemas
• Another way of defining document information

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Thats all folks

• Any questions?
• Optional XML exercise is availableanyone?
• Otherwise carry on with your coursework
• Next Tuesday Website management and last chance
  to finish off your website!
• and have a nice weekend ?