Type Inheritance and Relational Theory

Foreword

In this book, Chris Date describes some technical proposals due jointly to him and myself: viz., our proposed model of type inheritance. Those who are familiar with other aspects of our joint work, therefore, might be a little surprised to see that on this occasion I’m not a coauthor. However, I’m more than happy for Chris to have taken on this project tout seul, because the fact is—and I’m pleased to have the opportunity to state as much publicly here—it was Chris who came up with the basic ideas on which our inheritance model is based; Chris who proposed the terminology we used for those ideas; and Chris who originally drafted the various prescriptions, as we call them, that formally define that model.

In this foreword, I don’t need or even want to say much about our model as such (that’s what the book does); however, I do want to give my own recollections of the historical circumstances in which this work arose and certain events that helped both to motivate it and to shape it.

In the mid 1980s my career at IBM suffered for two or three years from an enforced absence from the database scene. (Previously I’d spent some fifteen years as a DBMS software developer, in particular playing a lead role in the development of a relational DBMS for commercial use called Business System 12.) When I returned to that scene in 1987, I found that two important developments had taken place during my absence:

1. SQL, a language that ten years earlier I had confidently predicted would “never ...