Chapter One. Introduction

Professionals in any discipline need to know the foundations of their field. So if you're a database professional, you need to know the relational model, because that model is the foundation (or a huge part of the foundation, anyway) of the database field in particular. Now, every course in database management, be it academic or commercial, does at least pay lip service to the idea of teaching the relational model but most of that teaching seems to be done very badly, if results are anything to go by. The relational model certainly isn't very well or very widely understood in the database community at large. Here are some possible reasons for this state of affairs:

• The model is taught in a vacuum. That is, for beginners at least, it's hard to see the relevance of the material, or it's hard to understand the problems it's meant to solve, or both.

• The instructors themselves don't fully understand or appreciate the significance of the material.

• (Most likely in practice.) The model as such isn't taught at all the SQL language or some specific dialect of that language, such as the Oracle dialect, is taught instead.

So this book is aimed at database professionals, especially commercial database practitioners, who have had some exposure to the relational model but don't know as much about it as they ought to. It's definitely not meant for beginners; however, it isn't a refresher course, either. To be more specific: I'm sure you know something about SQL, but and I apologize if my tone is somewhat offensive here if your knowledge of the relational model derives only from your knowledge of SQL, then I'm afraid you won't know the relational model as well as you should, and you'll probably know "some things that ain't so."

NOTE

SQL the relational model!

Here by way of illustration are some relational issues that SQL isn't too clear on (to put it mildly):

• What databases, relations, and tuples really are

• The difference between relations and types

• The difference between relation values and relation variables

• The relevance of predicates and propositions

• The legitimacy of relation-valued attributes

• The crucial role of integrity constraints

and so on (this isn't an exhaustive list). All of these issues, and of course many others, are addressed in this book.

I say again: if your knowledge of the relational model derives only from your knowledge of SQL, then you might know "some things that ain't so." One unfortunate consequence of this state of affairs is that you might find, in reading this book, that there are some things you have to unlearn and unlearning something is notoriously hard to do. And a related point . . . I'd like to recommend, politely, that you not skip the discussion of some topic because you think you're thoroughly familiar with that topic already. For example, are you sure you know exactly what a key is, in relational terms? Or a join?