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Schema Refinement: Normalisation, Decomposing Relations, Decomposition, Lossless-join Decomposition, Lossless-join, Dependency Preservation, Boyce-codd Normal Form, Third Normal Form, First Normal Form, Second Normal Form, Partial Functional Dependency, Normal Forms
Typology: Slides
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www.cl.cam.ac.uk/Teaching/current/Databases/
Decomposing relations
Data(sid,sname,address,cid,cname,grad e)
to a ‘better’ set of relation schema
Student(sid,sname,address) Course(cid,cname) Enrolled(sid,cid,grade)
then
such that
This is Tim’s somewhat non-standard definition….
Special Case: Lossless- join decomposition
decomposition of R with respect to an FD set F, if for every relation instance r of R that satisfies F,
R 1 (r)^ V^ …^ V^ Rk(r) = r
(this means project on the attributes of the relation’s schema)
Lossless-join: Example
sid sname addres s
cid cname grade
124 Julia USA 206 Database A++ 204 Kim Essex 202 Semantics C 124 Julia USA 201 S/Eng I A+ 206 Tim London 206 Database B- 124 Julia USA 202 Semantics B+
What happens if we decompose on (sid,sname,address) and (cid,cname,grade)?
Dependency preservation
Dependency preservation: example
Boyce-Codd normal form “Represent Every Fact Only ONCE”
BCNF: Example
BankerSchema(brname,cname,bname)
Third normal form
Prehistory: First normal form
Prehistory: Second normal form
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Not the end of problems…
Course Teacher Book Databases gmb Date Databases gmb Elmasri Databases jkmm Date Databases jkmm Elmasri OSF gmb Silberschatz OSF tlh Slberschatz
Decomposition