Download presentation

Presentation is loading. Please wait.

1
**5NF and other normal forms**

2
**Outline n-decomposability 3D constraint join dependency 5NF**

non-5NF - update anomalies problems in bringing a relation to 5NF other normal forms

3
**Always two projections?**

so far every relation was non-loss decomposable into two projections is this always possible? n-decomposable relations

4
**Courses - tutors - levels (CTL)**

5
**CTL - 2 attribute projections**

CL

6
**CTL - 3-decomposable the join of any two projections is not CTL; e.g:**

join(CT, TL) Extra!

7
**Constraint 3D Let R be a degree 3 relation. IF (a, b, x) R**

AND (a, y, c) R AND (z, b, c) R THEN (a, b, c) R

8
**Constraint 3D illustrated on the CTL relation**

IF tutor t1 teaches subject s1 AND level l1 studies subject s1 AND tutor t1 teaches level l1 THEN tutor t1 teaches subject s1 for level l1 note: this constraint is not expressed in CTL

9
**Constraint 3D and Join Dependency**

4NF does not express the constraint 3D the constraint 3D is a facet of a more general constraint: join dependency

10
Join dependency Let R be a relation. Let A, B, ..., Z be arbitrary subsets of R’s attributes. R satisfies the JD ( A, B, ..., Z ) if and only if R is equal to the join of its projections on A, B, ..., Z

11
5 NF R is in 5NF if and only if every join dependency in R is implied by the candidate keys of R 5NF is always achievable

12
Explanation a join dependency, (A, B, …, Z), is implied by the candidate keys, K1, …, Km of R if the fact that K1, …, Km are candidate keys for R determine the fact that R has the JD (A, B, …, Z)

13
**Illustration - positive example**

consider R (S_id, S_name, Status, City) with S_id and S_name candidate keys ({S_id, S_name, Status}, {S_id, City}) is a JD because S_id is a candidate key in R ({S_id, S_name}, {S_id, Status}, {S_name, City}) is a JD because S_id and S_name are both candidate keys in R

14
**Illustration - negative example**

consider CTL (Course, Tutor, Level) with (Course, Tutor, Level) - candidate key (and an extra constraint : constraint 3D) ({Course, Tutor}, {Course, Level}, {Tutor, Level}) is a JD, but this is not due to the CK, but to the constraint 3D if CTL had not had constraint 3D, would it have been in 5NF?

15
**Not 5NF - update anomalies**

CTL satisfies ( {Course, Tutor}, {Tutor, Level}, {Course, Level} ) insert (Programming, M. Ursu, Level2) what else must be done?

16
**Not 5NF - update anomalies**

CTL satisfies the same JD as before delete (Databases, M. Ursu, Level2) what else must be done?

17
**JDs and MVDs Fagin’s theorem restated**

R ( A, B, C ) satisfies ( AB, AC ) if and only if it satisfies the MVDs A B | C JD is the most general form of dependency (read as determination) possible between the attributes of a relation (in the relational model)

18
Activity Is 4NF subsumed by 5NF? Can you prove this using Fagin’s theorem and the definitions for 4 and 5 NF?

19
**Problems in bringing a relation to 5NF**

check whether all JDs are implied by the candidate keys Fagin : provides an algorithm for doing this for any relation, given all its JDs and all candidate keys discover all JDs for a given relation they do not have that intuitive meaning as FDs or MVDs

20
Concluding remarks 5NF is the ultimate normal form with respect to projection / join 5NF is guaranteed to be free of all anomalies that can be eliminated via projections determining whether a relation is in 4NF but not in 5NF is still fuzzy very rare in practice

21
**Recap JD - a more general constraint than MD**

a relation can be in 4NF and have un-expressed JDs this results in update anomalies such a relation can be decomposed (via projection) into an equivalent set of 5NF relations a relation is 5NF if all its JDs are deducible from its candidate keys for a relation in 4NF but not in 5NF, an unexpressed JD is a possible decomposition (towards 5NF)

22
**Other normal forms FDs, MVDs or JDs are not used**

domain-key normal form R is in DK/NF if and only if every constraint of R is a logical consequence of domain constraints and (candidate) key constraints restriction-union normal form decomposing operator: restriction abusing the language it can be said that: this normalisation theory is orthogonal on the “projection” normalisation theory

Similar presentations

Presentation is loading. Please wait....

OK

ALGEBRAIC EXPRESSIONS

ALGEBRAIC EXPRESSIONS

© 2018 SlidePlayer.com Inc.

All rights reserved.

To ensure the functioning of the site, we use **cookies**. We share information about your activities on the site with our partners and Google partners: social networks and companies engaged in advertising and web analytics. For more information, see the Privacy Policy and Google Privacy & Terms.
Your consent to our cookies if you continue to use this website.

Ads by Google

Ppt on world population day Ppt on success is failure turned inside out Ppt on heritage of indian culture Convert pdf ppt to ppt online shopping Ppt on switching devices in electronics Ppt on differential aptitude test Ppt on fuel cell Ppt on c language fundamentals worksheets Upload and view ppt online student Ppt on unsustainable to sustainable development