The XML or XSD (XML Schema Definition) schema is a standard defined by the W3C. Based on XML, XSC enables definition of XML document structure.

The aim of a schema is to define an XML class of document, and therefore the term "document instance" is often used to define a document that is valid in relation to certain criteria.

In order to allow the XML schema to reference XSD types, it is necessary to import the corresponding library. See "Importing the XSD Solution Pack".