However, the applications required arbitrary data types, which is nearly impossible for relational systems, according to experts. The data type concept is one of the concepts least understood by database practitioners. This is both a cause and a consequence of the failure by SQL and its commercially available dialects to implement relational domains , which are nothing but data types of arbitrary complexity. Fundamentals Databases are structured collections of facts about real-world entities. Substituting specific values for the placeholders turns the predicate into individual propositions.
Data types represent one kind of business rules, that constrain database values to be valid.
Two aspects of data types are poorly understood, if at all. The second aspect not sufficiently understood is that, aside from representations, a data type also includes operators for each representation exposed to users . Users can manipulate the values of a given type only with the operators made available for that type . For example, exposing the Fahrenheit representation to users means that the Temperature type must include operators for manipulating degrees Fahrenheit. Thus, data types are essentially one kind of integrity constraints on data values and operators , representing in the database one set of business rules.