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SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES LIS1510 Library and Archives Automation Issues XML and extensible systems Andy Dawson School of Library, Archive & Information Studies, UCL (University of Malta 2008) Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES What we will be covering today • • • • • Shortcomings of HTML Generalised markup languages How XML works XML document types Other related extensible technologies Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES Limitations of (X)HTML • Fixed tag set (specifications determined by W3C) • Intended for display of documents on the Web • Doesn’t do everything everyone wants • Not easy to use for other purposes – searching in documents – analysis of documents Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES Example of a Newspaper Name of newspaper Issue Article Headline Author Paragraphs Pictures Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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” Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES 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 Andy Dawson SCHOOL OF LIBRARY, ARCHIVE AND INFORMATION STUDIES That’s all folks… • Any questions? • Optional XML exercise is available…anyone? • Otherwise – carry on with your coursework • Next Tuesday: Website management and last chance to finish off your website! …and have a nice weekend Andy Dawson
