Database in Depth: Relational Theory for Practitioners
| These exercises are intended to serve as a review of the entire book, not just the present chapter. Some are repeats of exercises from earlier chapters.
Exercise 8-1
What exactly is the relational model? State as many differences as you can think of between SQL and the relational model. Why are SQL's departures from the relational model a bad thing? Exercise 8-2
What's The Information Principle? How might "row IDs" violate it? Exercise 8-3
What's a predicate? What's the connection between relations and predicates? Exercise 8-4
Do you believe relations are "flat" or two-dimensional? Justify your answer. Exercise 8-5
What's a join dependency? If relvar R satisfies the FD A
What's the real difference between a domain and a relation? Exercise 8-7
What's wrong with deferred integrity checking? Exercise 8-8
What's The Principle of Interchangeability? Exercise 8-9
What does first normal form really mean? Exercise 8-10
What's "the final normal form"? In what sense is it final? Exercise 8-11
What's the difference between a relation and a relvar? Exercise 8-12
What's The Principle of Orthogonal Design? Exercise 8-13
Would it make sense to define a relational comparison operator, "/" say, such that r / s gives TRUE if and only if r and s are disjoint (i.e., have no tuples in common)? Justify your answer. Exercise 8-14
Why is ORDER BY not a relational operator? Exercise 8-15
The difference between base relvars and views is that the former are physically stored and the latter aren't: true or false? Exercise 8-16
Why doesn't the relational model permit nulls? Or duplicates? Exercise 8-17
The relational model prescribes the data types that must be supported: true or false? Exercise 8-18
What's the difference between a primary key and a candidate key? Exercise 8-19
What's nonloss decomposition? Exercise 8-20
Should it ever be necessary to denormalize? Exercise 8-21
Product is a special case of join: true or false? Exercise 8-22
What's a type constraint? When are type constraints checked? Exercise 8-23
Can a relation have an attribute whose values are sets? Or arrays? Or relations? Exercise 8-24
Why do SQL's updates through a cursor violate the relational model? Exercise 8-25
Can a relation have no attributes at all? Exercise 8-26
What does it mean to say that the relational algebra is closed? Why is such closure important? Exercise 8-27
Any given relation r is identically equal to a certain restriction of r and a certain projection of r. Explain these observations. Exercise 8-28
Why is "materialized view" a contradiction in terms? Exercise 8-29
What's the difference between the relational model and an implementation thereof? Exercise 8-30
What's the crucial logical difference between a relational database and any other kind of database? (Hint: Remember The Information Principle.) Exercise 8-31
What's the difference between a true object/relational DBMS and a true relational DBMS? Exercise 8-32
Does restrict distribute over union? Over minus? Exercise 8-33
Does project distribute over union? Over minus? Exercise 8-34
How does XML fit with the relational model? Exercise 8-35
If you summarize an empty relation, what do you get? Exercise 8-36
What's the Closed World Assumption? Exercise 8-37
Define the operators semijoin and semiminus. Exercise 8-38
Define (a) BCNF, (b) 5NF, and (c) 6NF. Did it ever occur to you that the last two--4NF too, come to that are misnamed? Exercise 8-39
Is join commutative? Associative? Idempotent? Exercise 8-40
Every binary relvar is in BCNF: true or false? Exercise 8-41
What's the identity with respect to join? Exercise 8-42
What does it mean, formally or informally, to say an FD or JD is trivial? Exercise 8-43
Does a key that involves no attributes at all make any sense? What about a foreign key? Exercise 8-44
If a 3NF relvar has no keys that involve two or more attributes, that relvar is in 5NF: true or false? Exercise 8-45
Give at least three reasons why the result of a SELECT statement in SQL isn't a relation, in general. You can assume we're talking about an interactive environment, meaning we're not limited to "singleton SELECTs" (that is, SELECTs that retrieve at most one row). Exercise 8-46
Intersect is a special case of join: true or false? Exercise 8-47
Suppose relation r is of degree three. How many distinct projections does r have? Exercise 8-48
Suppose relvar R is of degree three. What's the maximum number of keys R can possibly have? What about FDs? Exercise 8-49
Are (relational) cartesian product and (relational) division inverse operations? Subsidiary question: Why did I say, specifically, relational cartesian product? Exercise 8-50
What's the join of n relations for n = 3? What about n = 1? And what about n = 0? Exercise 8-51
How can we do relational comparisons in SQL? Exercise 8-52
Does it make sense to declare keys for a view? Exercise 8-53
(a) Let the FD A Exercise 8-54
Which of the following identities are valid? a. r INTERSECT s
What do you understand by the term "semantic optimization"? Exercise 8-56
Why are relation-valued attributes usually contraindicated (at least in base relvars)? Exercise 8-57
"TABLE_DEE plays a role in the relational algebra analogous to that played by 0 in ordinary arithmetic." Explain this remark. Exercise 8-58
(a) Let Op be a monadic relational operator. What happens if the sole operand to Op is either TABLE_DUM or TABLE_DEE? (b) Let Op be a dyadic relational operator. What happens if each of the operands to Op is either TABLE_DUM or TABLE_DEE? Exercise 8-59
"There's only one relational model." Either justify this claim or state clearly why you disagree. Exercise 8-60
Why is it important for database professionals to be able to answer questions like these correctly? |