SQL and Relational Theory, 2nd Edition

DATABASE VARIABLES

Note: This section consists of a revised version of material from Appendix D (“What Is a Database?”) from the book Databases, Types, and the Relational Model: The Third Manifesto, by Hugh Darwen and myself (see Appendix G).

I mentioned in the previous section that databases are really variables (as I said in that section, if a database can be updated, then it’s a variable by definition). In other words, we can draw a distinction between database values and database variables, precisely analogous to the one we already draw between relation values and relation variables. As a matter of fact, we—i.e., Darwen and myself—did draw exactly such a distinction in the first version of The Third Manifesto. Here’s an edited quote:

The first version of this Manifesto distinguished databases per se (i.e., database values) from database variables ... It suggested that the unqualified term database be used to mean a database value specifically, and it introduced the term dbvar as shorthand for “database variable.” While we still believe this distinction to be a valid one, we found it had little direct relevance to other aspects of the Manifesto. We therefore decided, in the interests of familiarity, to revert to more traditional terminology. [In other words, we went on to use the term “database” to mean a database variable rather than a database value, and we didn’t use the terms “database variable” or “dbvar” at all.]

And of course I’ve done the same thing—I mean, I’ve used the ...