SQL and Relational Theory, 2nd Edition

EXERCISES

3.1 Define as precisely as you can the terms attribute, body, cardinality, degree, heading, relation, relation type, and tuple.

3.2 State as precisely as you can what it means for (a) two tuples to be equal; (b) two relations to be equal.

3.3 Write Tutorial D tuple selector invocations for a typical tuple from (a) the parts relvar, (b) the shipments relvar. Also show SQL’s counterparts, if any, to those selector invocations.

3.4 Write a typical Tutorial D relation selector invocation. Also show SQL’s counterpart, if any, to that selector invocation.

3.5 (This is essentially a repeat of Exercise 1.8 from Chapter 1, but you should be able to give a more comprehensive answer now.) There are many differences between a relation and a table. List as many as you can.

3.6 The attributes of a tuple can be of any type whatsoever (well, almost; can you think of any exceptions?). Give an example of (a) a tuple with a tuple valued attribute, (b) a tuple with a relation valued attribute (RVA).

3.7 Give an example of a relation with (a) one RVA, (b) two RVAs. Also give two more relations that represent the same information as those relations but don’t involve RVAs. Also give an example of a relation with an RVA such that there’s no relation that represents precisely the same information but has no RVA.

3.8 Explain the relations TABLE_DUM and TABLE_DEE in your own words. Why exactly doesn’t SQL support them?

3.9 As we saw in the body of the chapter, TABLE_DEE means TRUE and TABLE_DUM means FALSE. ...