Many businesses have acquired and implemented various database technologies. Although XML extensions are available for many relational database products, XML is not in itself a database. However, XML is often used to describe data extracts from, insertions into, and exchanges between application systems and their respective databases. A frequent challenge encountered by the data architect when data are exchanged between different systems is variation in database data type support. A data type supported by one database product could be vastly different from the same data type defined to another database. Often, the solution to disparate data type support includes a process of mapping source data types to target data types and the resulting transformation.

Tables 4.3 through 4.7 describe the most common data types supported by several database products and mapped to data types supported by frequently used W3C XML Schemas. In some cases, a W3C XML Schema data type may not have a direct relationship to a corresponding database data type. In other cases the W3C XML Schema data type may be supported by the database, but minimum and maximum values and default format may differ.