Databases of many kinds exist in terms of their associated data model differences and vendor differences. Regarding differences among data models, each has different data representation, and unique associated manipulation. Some typical examples include the table type of relational databases (RDB), XML-representation type of XML databases (XMLDB), and object-oriented databases (OODB). Even the same model database might have different features among vendors. Regarding RDB for example, there might be some differences in SQL and/or data type representation. The typical example is that we have MySQL, PostgreSQL, and SQLServer, each of which has a different vendor.