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Carnegie Mellon Univ. Dept. of Computer Science 15-415 - Database Applications

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### Carnegie Mellon Univ.Dept. of Computer Science15-415 - Database Applications

C. Faloutsos

Relational domain calculus

General Overview

- relational model
- Formal query languages
- relational algebra
- rel. tuple calculus
- rel. domain calculus

15-415 - C. Faloutsos

Overview - detailed

- rel. tuple calculus
- dfn
- details
- equivalence to rel. algebra
- rel. domain calculus + QBE

15-415 - C. Faloutsos

Rel. domain calculus (RDC)

- Q: why?
- A: slightly easier than RTC, although equivalent - basis for QBE.
- idea: domain variables (w/ F.O.L.) - eg:
- ‘find STUDENT record with ssn=123’

15-415 - C. Faloutsos

Details

- but: domain (= column) variables, as opposed to tuple variables, eg:

ssn

address

name

15-415 - C. Faloutsos

Reminder: our Mini-U db

15-415 - C. Faloutsos

Examples

- (projection) find name of student with ssn=123

need to ‘restrict’ “a”

RTC:

15-415 - C. Faloutsos

‘Proof’ of equivalence

- rel. algebra <-> rel. domain calculus

<-> rel. tuple calculus

15-415 - C. Faloutsos

Overview - detailed

- rel. domain calculus
- why?
- details
- examples
- equivalence with rel. algebra
- more examples; ‘safety’ of expressions

15-415 - C. Faloutsos

Reminder: our Mini-U db

15-415 - C. Faloutsos

Sneak preview of QBE:

15-415 - C. Faloutsos

Sneak preview of QBE:

- very user friendly
- heavily based on RDC
- very similar to MS Access interface

15-415 - C. Faloutsos

More examples

- 3-way join: find names of students taking a 2-unit course - in RTC:

join

projection

selection

15-415 - C. Faloutsos

More on division

- find students that take all the courses that ssn=123 does (and maybe even more)

15-415 - C. Faloutsos

More on division

- find students that take all the courses that ssn=123 does (and maybe even more)

15-415 - C. Faloutsos

Overview - detailed

- rel. domain calculus + QBE
- dfn
- details
- equivalence to rel. algebra

15-415 - C. Faloutsos

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