Ever since the relational view concept was first invented, view updating has been a contentious issue. Support in todays SQL products is ad hoc and meager at best. The SQL standard is even more impenetrable in this area than it usually is. Even the research literature is weak on this topic; numerous approaches have been proposed and found wanting over the years. This presentation, by contrast, describes a way of looking at the problem that (a) appears to be logically correct, (b) is certainly not ad hoc, and (c) works for all kinds of views. The overall message is: Views in general are just as updatable as base tables are!

The presentation is divided into four modules. Module I explains why the view update problem is important, shows how not to do it, and presents a general framework within which the problem can sensibly be addressed. Module II introduces certain fundamental principles, including The Assignment Principle, The Golden Rule, and The Principle of Interchangeability, and discusses the concept of information equivalence. Module III consists of a detailed discussion of a motivating example, using that example to introduce the important concept of compensatory actions. Finally, Module IV ties everything together by showing how concepts introduced in the first three modules can be used as a basis for solving the problem.






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