XML InfoSet

The XML information set (Infoset) is a description of the information available in a well-formed XML document.  The XML information set does not require or favor a specific interface or class of interfaces. However, the XML InfoSet specification presents the information set as a tree for the sake of clarity and simplicity.   There is no requirement that the XML information set be made available through a tree structure; other types of interfaces, including (but not limited to) event-based and query-based interfaces are also capable of providing information conforming to the information set.  As long as the information in the information set is made available to XML applications in one way or another, the requirements of XML InfoSet are satisfied.

An XML document's information set consists of two or more information items (the information set for any well-formed XML document will contain at least the document information item and one element information element). An information item is an abstract representation of some component of an XML document: each information item has a set of associated properties, some of which are core, and some of which are peripheral.

For any given XML document, there are a number of corresponding information sets: a unique minimal information set consisting of the core properties of the core items and nothing else, a unique maximal information set consisting of all the core and all the peripheral items with all the peripheral properties, and one for every combination of present/absent peripheral items and properties in between. The in-between information sets must be fully consistent with the maximal information set.

All information sets are understood to describe the XML document with all entity references already expanded; that is, represented by the information items corresponding to their replacement text. In the case that an entity reference cannot be expanded, because an XML processor has not read its declaration or its value, explicit provision is made for representing such a reference in the information set.

XML Infoset became a W3C Proposed Recommendation on August 10, 2001.