Thus, the DBMS must also support, for every operator, data types for all its possible result values, which, as in the project ratio case, may well be distinct types. Suppose the company uses employee fingerprints for security. The relational model works with any data type, no matter how complex, as long as proper operators are provided. It will simply apply the operators, no questions asked. This requirement means that DBMSs must be user-extendible.
Users have access to user-defined data types only via the operators programmed into such types .
This has some serious practical implications for the design of DBMSs and databases. For those implications and how the object and relational approaches tackle them, stay tuned for future articles. Or read about them today in the book .