Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
8 Cards in this Set
- Front
- Back
|
What does it mean to say that Relational Algebra and Calculus are equivalent in expressive power?
|
That any relational algebra expression can be written as a relational calculus expression and vice versa
|
|
|
What does it mean to say that relational calculus is based on the idea of First Order Logic?
|
It means tat Relational Calculus is declarative not procedural. Also it means that it does not show how to perform the operation, but rather is a declaration of what is wanted.
|
|
|
This part of a RC expression states tat the tuple x is a member of the relation R.
|
Range Relation
In this expression 't' is a member of the relation Employee {t | EMPLOYEE(t) AND t.Salary>5000 |
|
|
{t.Bdate, t.Address | EMPLOYEE(t) AND t.Fname=‘John’ AND t.Minit=‘B’ AND t.Lname=‘Smith’}
What is retrieved by the above expression? |
Birthday and Address attributes are retrieved
|
|
|
A single element of a formula of relational Calculus.
|
Atom
|
|
|
This is a Boolean expression, composed of one ore more atoms connected via logical operators (AND, OR, NOT)
|
Formula
|
|
|
What are the two rules of formulas?
|
1) Every Atom is a Formula
2) if F1 is a formula and F2 is a formula, then the following are all a formula: (F1 AND F2) (F1 OR F2) NOT(F1) NOT(F2) |
|
|
What are bound variables and what is their significance?
|
Bound Variables are attached to quantifiers and give them meaning. Without Bound Variables quantifiers are meaningless. At "for all t" and Et "there exists a t"
|
