Extensible Markup Language

From Unofficial BOINC Wiki

[edit] General

A method of defining the content of a message and the data in the message using plain-text. The intent is to create a communication exchange mechanism that enables the same plain-text to be both context and data.

A subset of the Standard Generalized Mark-Up Language (SGML) and is primarily intended to enable communication on the Internet.

The flaws in this new "Silver-Bullet" are that the ratio of content to description is very high. This means that 90% of the communication is a description of the data and that the actual data content of the message is only 10% of the actual transmission. The other flaw is that the description of the data that is embedded within the message makes it easier for anyone that intercepts the message to understand the actual content of the message (in other words, you can't hide the meaning without encryption).

In the context of the BOINC System Software this is one of the mechanisms that is used to exchange information between your BOINC System Software and the Project's Data Server.

Extensible Markup Language, (abbreviated XML), describes a class of data objects called XML documents and partially describes the behavior of computer programs which process them. XML is an application profile or restricted form of SGML, the Standard Generalized Markup Language [ISO 8879]. By construction, XML documents are conforming SGML documents.

XML documents are made up of storage units called entities, which contain either parsed or unparsed data. Parsed data is made up of characters, some of which form character data, and some of which form markup. Markup encodes a description of the document's storage layout and logical structure. XML provides a mechanism to impose constraints on the storage layout and logical structure.

The design goals for XML are:

• XML shall be straightforwardly usable over the Internet.
• XML shall support a wide variety of applications.
• XML shall be compatible with SGML.
• It shall be easy to write programs which process XML documents.
• The number of optional features in XML is to be kept to the absolute minimum, ideally zero.
• XML documents should be human-legible and reasonably clear.
• The XML design should be prepared quickly.
• The design of XML shall be formal and concise.
• XML documents shall be easy to create.
• Terseness in XML markup is of minimal importance.

This specification, together with associated standards (Unicode and ISO/IEC 10646 for characters, Internet RFC 3066 for language identification tags, for language name codes, and ISO 3166 for country name codes), provides all the information necessary to understand XML Version 1.0 and construct computer programs to process it.

From the W3C XML spec; courtesy: NeoAmsterdam (Profile)