Worldwide Web Consortium (W3C)

• Started developing XML in 1996
• Draft specification released in November 1996
• Extended and expanded during 1997
• Formal specification recommended in December 1997

By 1998 there was no real mainstream use of XML - no mass uptake of XML

• Lack of development opportunities
• Lack of general awareness of
  • Its principles
  • Its opportunities

During 1998 things began to change

• Applications supporting XML became available
  • XML-capable browsers
  • XML parsers
• Applications developed using XML
  • Pioneers were
    • W3C sponsors like Adobe
    • Web developers
• Accessible documentation began to appear

XML is a metalanguage

A metalanguage is a language used to describe another language

XML describes the data content but NOT its presentation - Which is what makes it so important in web development: It seperates the data from its presentation. It is also the main difference between XML and HTML.

From a distance XML looks like HTML

• Uses tags
• Uses <> chevrons to identify tags
• Uses plain text, human-readable tags

But XML is extensible and HTML is not

• The developer decides what is included in XML documents (It has a document type definition or DTD to achieve this)

The HTML specification defines what is in a HTML document

• The HTML standards impose a fixed set of allowable tags and syntax

Well-formed and valid

An XML document is well-formed if it contains no errors (it matches the W3C XML standards).

It is valid if it conforms to its DTD.

XML documents are validated against their DTDs but a DTD is not mandatory. If there is no DTD the document can't be a valid XML document.

What have I got to say about XML that hasn't already been said?

Not a lot that's new, really. Just a developer's view of the technology.

I don't have any serious spin to put on a discussion of XML but what I do say is probably influenced by its practical advantages in development.

XML files are usually saved with a .XML extension:

• SALES.XML
• XML-enabled web browsers recognise XML files by this extension

XML parsers - and other XML applications programs - will open XML documents irrespective of their extensions. They recognise XML by

• A processing instruction line:
  • <?xml verson"1.0" standalone"yes"?>
• The files' content

Development

Creating an XML document consists combining data with XML tags

XML documents can be created by hand. They can be written n Notepad hand-codng data values and ther assocated tags

For dynamc XML documents - fles in which the data content changes - the data need to be supplied from, say, a database, then wrapped in XML tags.