Tuple Relational Calculus
Tom Kelliher, CS 318
Feb. 22, 2002
Homework due Wednesday. E/R designs due today @ 5:00 PM.
Read 7.3 for Wednesday.
- Introduction to TRC.
Domain relational calculus.
- SQL is based upon this.
- Simple example TRC query:
FROM Teaching T
WHERE T.Semester = 'F1997';
- General form of a TRC query:
- T is a tuple variable which ranges over all possible
values of tuples.
- Condition is:
- , asserting that T is in relation R.
- or .
- Two conditions combined using AND or OR, or one condition
modified by NOT.
- A condition (C), Relation (R), and tuple variable (T) combined
- T may be the only free (vs. bound) variable.
- This shorthand extension is acceptable:
where T.A and S.B are the only free variables. Meaning? (Implied
- Meaning of a TRC query:
The result of a TRC query with respect to a given database is the set
of all choices of values for the variable T that make the query condition a
true statement about the database.
Implies an exhaustive search over the tuple space.
- All courses that have been taken by every student:
Requires division in relational algebra!
- Find all students who have ever taken a course from every professor
who has ever taught a course. Why doesn't this express that?
How do we fix this?
- Retrieve IDs of students who did not take any courses in F2001:
- Find potential student graders for this semester's courses:
Hard way, similar to SQL query we developed earlier:
Write TRC queries to answer the following:
- Retrieve name of student with largest ID number.
- Names of all professors who have taught CS318.
- The names of all sophomores who received A's during the F2001
- The IDs of all students who took exactly one course during the F2001
- The IDs of all students who have taken a course with me.
- The IDs of all students who have taken every course I've taught.
Thomas P. Kelliher
Wed Feb 20 18:21:28 EST 2002