Appendix C. Answers to Exercises

Chapter 1

Exercise 1-1. Here are a few examples of statements from the early part of the chapter where the term relation should be replaced by the term relvar:

  • “Every relation has at least one candidate key.”

  • “A foreign key is a set of attributes in one relation whose values are required to match the values of some candidate key in some other relation (or possibly the same relation).”

  • “[The] relational assignment operator…allows the value of some relational expression…to be assigned to some relation.”

  • “A view (also known as a virtual relation) is a named relation whose value at any given time t is the result of evaluating a certain relational expression at that time t.”

And so on.

Exercise 1-2. E. F. Codd (1923–2003) was the original inventor of the relational model, among many other things. In December 2003 I published a brief tribute to him and his achievements, which you can find on the ACM SIGMOD website and elsewhere. An expanded version of that tribute appears in my book Date on Database: Writings 2000-2006 (Apress, 2006).

Exercise 1-3. A domain can be thought of as a conceptual pool of values from which actual attributes in actual relations take their actual values. In other words, a domain is a type, and the terms domain and type are effectively interchangeable—but personally I much prefer type, as having a longer pedigree (in the computing world, at least). Domain is the term used in most of the older database literature, ...

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