Download Exam Discussion-AIC

CS 319: Theory of Databases:
Exam preparation
Dr. Alexandra I. Cristea
http://www.dcs.warwick.ac.uk/~acristea/
Structure
• 3 hours, 100% of module mark
• You will answer FOUR questions out of
six.
• This year’s exam format is here.
• Read carefully *all* text of a question.
• look at: the exams given previously.
(the uni doesn’t have them anymore!)
Books
• See also Database System Concepts
(DSC), 5th Edition, Silbershatz, Korth,
Sudarshan
– Or 6th edition equivalent
– chapters mentioned in the following
• See also: Hugh's book based on
CS252, a free download from
BookBoon.com
Topics
1. Database generalities, Functional
Dependencies, (Non-)Redundancy,
Closure, Cover
2. Armstrong Axioms, Decompositions
3. Relational Algebra, query optimization
4. Tuple calculus, Domain calculus, Query
equivalence
5. SQL and the relational model, How not to
Use NULLs
6. Temporal Databases
1. Database generalities,
Functional Dependencies, (Non)Redundancy, Closure, Cover
• What do I need to know?
• Database generalities :
– Introduction – AIC; see also DSC Chapter 1:
Introduction
• Functional Dependencies :
– Proving FD - AIC; see also DSC Chapter 7:
Relational Database Design
• (Non-)Redundancy, Closure, Cover:
– Proving (Non)Redundancy; Closure, Cover –
AIC; see also DSC Chapter 7: Relational
Database Design
2. Armstrong Axioms,
Decompositions
• What do I need to know?
• Armstrong Axioms
– Armstrong - CompleteSound – AIC ; see also
DSC Chapter 7: Relational Database Design
– See also other examples
• Decompositions
– Decompositions: Dependency Preserving,
Lossless Join ; see also DSC Chapter 7:
Relational Database Design
– See all NF simple description
– See also a paper on the subject
3. Relational Algebra, query
optimization
• What do I need to know?
• Relational Algebra:
– RA-AIC; see also DSC Chapter 2:
Relational Model
• Query Optimisation:
– Query Optimization- AIC; see also DSC
Chapter 14: Query Optimization
4. Tuple calculus, Domain
calculus
• What do I need to know?
• Tuple Calculus
– Tuple Calculus – AIC
• Domain Calculus
– Domain Calculus – AIC
• Query equivalence
– Query equivalence - AIC
5. SQL and the relational
model, How not to Use
NULLs
• What do I need to know?
• SQL and the relational model
– The Askew Wall (SQL and The Relational
Model) pay attention to the international
standard!
– Slides
– Notes
• How not to Use NULLs
– How to Handle Missing Information Without
Using NULL
– Slides
– Notes
• See also: Hints regarding exam
questions on Hugh's lectures
• See also: Past exam questions
6. Temporal Databases
• What do I need to know?
• Temporal Data
– Temporal Data and The Relational Model
– Slides
– Notes
– Pay attention to the 2011 temporal
extension to SQL
• See also: Hints regarding exam
questions on Hugh's lectures
• See also: Past exam questions
• See also: Exercises on Temporal Data
• Questions?
19
Q&A
• Will each topic contain questions from all subjects mentioned
in the title?
– No. They represent the pool of information from which questions are
asked. See also last year’s exam.
• How long should I spend on one topic?
– Max around 45 min (45*4=180min = 3 hours)
• Why are there differences in structure to previous year?
– Regulations. Also due to the overlap with CS253, less emphasis is put
on the overlapping topics.
• ‘See Also’: what do I do with them?
– Make sure you read them at least once. There will be no questions
directly related to those parts (unless definitions are given specifically),
but it helps contextualise the information.
20
Beer database
• serves(k,b) : bar k serves beer b
• likes(d,b)
: drinker d likes beer b
• visits(d,k)
: drinker d visits bar k
Beer question (tupel calculus)
• Give all beers that are served in bars where none of
the visitors like any other beer (than the ones
served in that bar).
•
Is this a correct answer?
{t | s  S ( s[b]  t[b]  v  V ((v[k ]  s[k ]) 
(l  L((l[d ]  v[d ])  (ss  S ( ss[k ]  s[k ]  l[b]  ss[b])))))}
A faulty answer
• Consider
{t | s  S ( s[b]  t[b ] 
v V (v[ k ]  s[ k ]  l  L (l [d ]  v[ d ]  l[ b]  s[b])))}
• Or after a rewrite
{t | s  S ( s[b]  t[b ] 
v V (v[k ]  s[k ]  l  L( l[ d ]  v[d ]  l[ b]  s[b])))}
• Suppose there are 2 beers a, b, 1 bar k, 2 drinkers x, y;
everyone serves/visits/likes everything Then the correct answer should
result in {a, b}.
The tupel calculus expression does not contain a, because every visitor
of k also likes b.
Beer question (RA)
• Give all beers that are served in bars where none of
the visitors like any other beer (than the ones served
in that bar).
• b(S  (k(S) - k( V  L - V  L  S)))
• This is not so easy to translate to the earlier TC
expression
Common tupel calculus mistakes
• Explain what is wrong in the following queries:
1. {t | s  S (s[b]  t[b]  v V (l  L(l[b ]  s[b])))}
2. {t | s  S (s[b]  t[b]  l  L(l[b ]  s[b]  v V (l[d ]  s[d ])))}
3. {t | s  S ( s[b]  t[b]  v V (v[k ]  s[k ]  l  L
(l[d ]  v[d ]  ss  S ( s[k ]  ss[k ]  ss[b]  l[b]))))}
4
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5
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6 {t | s  S ( s[b]  t[b]  v V (v[k ]  s[k ] 
l  L( v[d ]  l[d ]  l[b]  s[b])))}
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8 {s | s  S  (v : v V  v[ k ]  s[ k ] : ( l : l  L : v[ d ]  l[ d ] 
( w : w  S  w[k ]  s[ k ]  l[b]  w[b])))}
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9 {
10 {t | s  S ( t[b ]  s[ b])  v V (v[k ]  s[k ]) 
l  L( l[b ]  s[ b]  v[ d ]  l[ d ])}
11 {t | s  S ( s[b]  t[b ]  v V (v[k ]  s[k ] 
l  L (l[ d ]  v[ d ]  r  S ( r[ k ]  v[k ]  r[b]  v[ b]))))}
12 {t | t  bar  serves(beer , drinkr )}
13 {t | s  S (t [b]  s[b ]  v V ( v[ k ]  s[ k ] 
l  L (l[ d ]  v[ d ]  l[b ]  s[ b])))}
14 {t | s  S ( s[b]  t[b ]  v V (v[ k ]  s[ k ] 
l  L( l[b ]  s[ b]  l [d ]  v[ d ])))}
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15 {
16 {t | l  L( s  S (l[b ]  s[b ]  v V
( v[ d ]  s[ d ]  v[ k ]  s[ k ]  t[b]  s[b ])))}
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17 {
18 {t | l  L( s  S (l [b]  s[b]  v V
( v[ d ]  s[ d ]  v[ k ]  s[k ]  t [b]  s[b])))}