Introducing XMLPART 1

"XML", as we all know, is an acronym for Extensible Markup Language.

Markup is a method of conveying metadata (information about another dataset).

SGML-based markup languages all use literal strings of characters, called tags to delimit the

major components of the metadata, called elements.

SGML is an acronym for Standard Generalized Markup Language, an older and more much

complex markup language than XML. It has been codified as an international standard by the

ISO (International Organization for Standardization) as ISO 8879 and WebSGML.

Separation of Semantics and PresentationXML is all about the description of data, with nothing said about its presentation.

HTML combines some rudimentary descriptive markup, plus a great deal of markup

that describes the presentation of the data.

The initial layer of XML processing is the XML parser, which can optionally use a DTD or schema

to describe and validate the XML data.

The application layer of XML processing, such as a browser or editor, can use an XSL

style sheet to describe the presentation of the XML data.

XML data can be used for computer-to-computer messages, as well as for humanreadable

documents.

XML text and names may use any of the world's different alphabets, scripts, and

writing systems as defined in the ISO/IEC 10646 and Unicode 3.0 standards.

Internationalization (I18N)XML text and names may use any of the world's different alphabets, scripts, and

writing systems as defined in the ISO/IEC 10646 and Unicode 3.0 standards.

Internationalization (I18N)XML text and names may use any of the world's different alphabets, scripts, and

writing systems as defined in the ISO/IEC 10646 and Unicode 3.0 standards.

XML is a text format that is easily transmitted over the Internet and other

communications links. XML works with basic WWW protocols, including HTTP or

HTTPS.

XML will enable an enhanced WWW architecture. XML can also be used as a

universal data exchange and long-term storage format, with or without the Internet.

XML is constrained by design to be interoperable with SGML.

The Organization for the Advancement of Structured Information Standards (OASIS) is a non-

profit, international consortium that is devoted to accelerating the adoption of product-

independent vocabularies based upon public standards, including SGML, HTML, and XML.

Well-formed XML data conforms to the XML syntax specification, and includes no

references to external resources (unless a DTD is provided). It is comprised of

elements that form a hierarchical tree, with a single root node (the document element).

Valid XML data is well-formed, and it conforms to additional validity constraints of

the XML syntax specification and those defined in a DTD or schema.

SGML Note: The SGML equivalent of a well-formed document is known as tag-valid. The SGML

equivalent of a valid document is type-valid.

ParsersThere are two types of parsers:

Non-validating – the parser merely ensures that a data object is well-formed XML

Validating – the parser uses a DTD (or other type of schema) to ensure the validity of a

wellformed data object's form and content

DTDsDTDs are an integral part of the XML 1.0 Recommendation, although they do not use XML syntax