XML data model

Sequences and items
The XPath data model is based on the notion of a sequence. The value of an XPath expression is always a sequence. A sequence is an ordered collection of zero or more items. An item is either an atomic value or a node.

Atomic values
An atomic value is an instance of one of the built-in atomic data types that are defined by XML Schema.

Nodes
A node conforms to one of the types of nodes that are defined for XPath. These node types include: document, element, attribute, text, processing instruction, comment, and namespace nodes.

Data model generation
Before an XPath expression can be processed, the input documents must be represented in the XML data model.

XML values in SQL
In terms of the XQuery/XPath 2.0 data model, DB2 for i SQL defines an XML value as a sequence that contains a single document node, with a sub-tree containing the document's content. Representing an XML value as a document node guarantees that the value can be serialized to a character representation that exactly represents the XML value. This definition is referred to as XML(CONTENT) in the 2008 Database Language SQL Part 14 - XML-Related Specifications (ISO 9075-14).