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Objectives ................................................................................................................................................ 1
7.1 Introduction to Markup Languages ................................................................................................ 2
7.1.1 SGML ................................................................................................................................ 2
7.1.2 HTML ................................................................................................................................ 2
7.1.3 XML .................................................................................................................................. 2
7.1.4 Relationship ....................................................................................................................... 3
7.2 XML Primer ................................................................................................................................... 3
7.2.1 Validity and Well-Formedness .......................................................................................... 4
7.2.2 XML Declaration ............................................................................................................... 4
7.2.3 Encoding: Unicode ............................................................................................................ 4
7.2.4 Document Type Definition (DTD) .................................................................................... 5
7.2.5 Elements / Tags.................................................................................................................. 6
7.2.6 Entities ............................................................................................................................... 7
7.3 Creating your own ML based on XML .......................................................................................... 7
7.4 Parsing and Processing XML ......................................................................................................... 8
7.4.1 SAX ................................................................................................................................... 8
7.4.2 DOM .................................................................................................................................. 9
7.4.3 SAX vs DOM .................................................................................................................. 10
7.5 XML Namespaces ........................................................................................................................ 10
7.5.1 Default Namespaces ........................................................................................................ 11
7.5.2 Explicit Namespaces ........................................................................................................ 11
7.6 XML Schema ............................................................................................................................... 11
7.6.1 Schema Structure ............................................................................................................. 11
7.6.2 Sequences ........................................................................................................................ 11
7.6.3 Nested Elements .............................................................................................................. 12
7.6.4 Extensions ........................................................................................................................ 12
7.6.5 Attributes ......................................................................................................................... 12
7.6.6 Named Types ................................................................................................................... 12
7.6.7 Other Content Models ...................................................................................................... 13
7.6.8 Schema Namespaces ........................................................................................................ 13
7.6.9 Schema Example ............................................................................................................. 13
7.7 Data and Metadata ....................................................................................................................... 15
7.7.1 Metadata Standards .......................................................................................................... 15
7.7.2 Metadata Transformation ................................................................................................. 15
7.8 XPath ........................................................................................................................................... 16
7.8.1 XPath Syntax ................................................................................................................... 16
7.9 XSL .............................................................................................................................................. 17
7.10 XSLT........................................................................................................................................ 17
7.10.1 XSLT Templates ............................................................................................................ 17
7.10.2 XSLT Special Tags ........................................................................................................ 17
7.10.3 XSLT Language............................................................................................................. 17
7.10.4 XSLT Example .............................................................................................................. 18
7.11 Answers.................................................................................................................................... 19
7.11.1 Answer to Activity 1 ...................................................................................................... 19
Objectives
At the end of this chapter you will be able to:
• Explain different markup languages;
• Parse and process XML;
• Use the various XML attributes.
, XML
7.1 Introduction to Markup Languages
XML (eXtensible Markup Language) is a markup language for documents that contain structured information.
Markup refers to auxiliary information interspersed with text to indicate structure and semantics. Documents does not
only refer to traditional text-based documents, but also to a wide variety of other XML data formats, including
graphics, mathematical equations, financial transaction over a network, and many other classes of information.
Examples of markup languages include LaTex, which uses markup to specify formatting (e.g. \emph), and HTML which
uses markup to specify structure (e.g. <p>). A markup language specifies the syntax and semantics of the markup tags.
Here is a comparison between plain text and marked up text:
Plain text:
The quick brown
fox jumped over the lazy dog.
Marked up text:
*paragraphstart*The *subjectstart*quick brown fox
*subjectend* *verbstart*jumped*verbend* over the *objectstart*
lazy dog*objectend* .*paragraphend*
Marked up text aids in semantic understanding, since more information is associated with the sentence than just text itself.
This also makes it possible to automatically (i.e. by computer) translate to other formats.
7.1.1 SGML
SGML (Standard Generalised Markup Language) specifies a standard format for text markup. All SGML documents
follow a Document Type Definition (DTD that specifies the document's structure). Here is an example:
Can you see why SGML does not require end tags? Find out more about SGML on the Internet. As a starting
point, look at the SGML resources page on the W3 Consortium website [http://www.w3.org/MarkUp/SGML/]. Also
search for SGML on Google [http:// www.google.com
7.1.2 HTML
HTML (HyperText Markup Language) specifies standard structures and formatting for linked documents on the World
Wide Web. HTML is a subset of SGML. In other words, SGML defines a general framework, while HTML defines
semantics for a specific application.
To Do: HTML
HTML is used to specify both the structure and the formatting of Web documents. Examine the list of HTML tags that
you have learnt so far and decide which group each tag belongs into. Read up more on the HTML section of the W3
page [http://www.w3.org/MarkUp/].
7.1.3 XML
2
, XML
XML, a subset of SGML, was introduced to ease adoption of structured documents on the Web. While SGML has been the
standard format for maintaining such documents, its suitability for the Web was poor (for various technical reasons,
some of which are discussed later; however, some are beyond the scope of this course). SGML conformity means that
XML documents can be read by any SGML system. However, the upside of XML is that XML documents do not
require a system capable of understanding the full SGML language.
Both HTML and SGML were considered unsuitable for the use that XML was put to. HTML specifies the semantics of a
document (which in HTML's case denotes formatting), but does not provide arbitrary structure. SGML however, does
provide arbitrary structure, but is too complex to implement in a Web browser. XML was not designed to replace SGML.
As a result, many companies use a SGML to XML filter for their content.
7.1.4 Relationship
The figure below illustrates the relationship between SGML, HTML, XML, and XHTML. XHTML is discussed later in
the chapter.
7.2 XML Primer
An XML document is a serialised segment of text which follows the XML standard (which can be found at the W3C
site [http://www.w3.org/TR/REC-xml]).
To Do: Goals of XML
XML's goals are set out in the W3C recommendations [http://www.w3.org/TR/REC-xml/#sec-origin-goals]. Read
these recommendations and, if some points are unclear, find out more about them.
An XML document may contain the following items:
• a XML declaration
• DTDs
• text
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