The semantics of the core features of XML Schema in terms of XQuery 1.0 and XPath 2.0 data model algebraically defined is given. The database state is represented as a many sorted algebra whose sorts are sets of data type values and different kinds of nodes and whose operations are data type operations and node accessors. The values of some node accessors, such as "parent", "children" and "attributes", define a document tree with a definite order of nodes. The values of other node accessors help to make difference between kinds of nodes, learn the names, types and values associated with the corresponding document entities, etc., i.e., provide primitive facilities for a query language. As a result, a document can be easily mapped to its implementation in terms of nodes and accessors defined on them.