The word relational is also used somewhat inappropriately by several vendors to refer to their products as a marketing gimmick. To qualify as a genuine relational DBMS, a system must have at least the following properties (Note 1):
1. It must store data as relations such that each column is independently identified by its column name and the ordering of rows is immaterial.
2. The operations available to the user, as well as those used internally by the system, should be true relational operations; that is, they should be able to generate new relations from old relations.
3. The system must support at least one variant of the JOIN operation.
Although we could add to the above list, we propose these criteria as a very minimal set for testing whether a system is relational. It is easy to see that some of the so-called relational DBMSs do not satisfy these criteria.
We begin with a description of Oracle, currently one of the more widely used RDBMSs. Because some concepts in the discussion may not have been introduced yet, we will give references to later chapters in the book when necessary. Those interested in getting a deeper understanding may review the appropriate concepts in those sections and should refer to the system manuals.