The Relational Database Dictionary

Introduction

This dictionary contains more than 600 entries dealing with issues, terms, and concepts involved in, or arising from use of, the relational model of data. Many of the entries include not only definitions but also one or more illustrative examples. I’ve done my best to make the definitions as clear, precise, and accurate as possible; they’re based on my own best understanding of the material, an understanding I’ve been honing gradually over some 35 years of involvement in this field.

I’d like to stress the point that the dictionary is, as advertised, relational. To that end, I’ve deliberately omitted terms and concepts that are only tangentially connected to relational matters (e.g., almost all details of the supporting type theory, including type inheritance details in particular). I’ve also omitted various topics that are part of database technology in general and aren’t particular to relational databases (e.g., security issues, the log, recovery and concurrency control, and so forth). What’s more, I’ve also omitted certain SQL terms and concepts that—the fact that SQL is supposed to be a relational language notwithstanding—aren’t really relational at all (outer join, UNION ALL, and updating through a cursor are examples). That said, I should add that I have deliberately included a few nonrelational terms in order to make it clear that, contrary to popular opinion, the concepts in question are indeed not relational (index is a case in point here).

I must explain too ...