XML Schema Complete Reference, The

24.16. restriction Element

The restriction element is used to derive a complexType from another by restricting constraining facets for simple content and altering attribution and substitutions for complex content. A database designer has two major options in designing a schema to create a restriction:

• Add a type column to a table and handle the restrictions in check clauses and triggers that key off of the type column. In other words, add the type to the existing set of tables.

• Create a (partially) separate set of tables to handle the new type.

Each of these approaches has trade-offs. The first approach is best when the restriction element type is associated with content that is mapped to database columns and not relationships; it best handles ...