Hesse pencil: Difference between revisions
Jump to navigation
Jump to search
en>R.e.b. Clean up |
downcase |
||
Line 1: | Line 1: | ||
A '''canonical cover''' <math>F_c</math> for F (a set of [[Functional dependency|functional dependencies]] on a [[Relation (database)|relation scheme]]) is a set of dependencies such that F logically implies all dependencies in <math>F_c</math>, and <math>F_c</math> logically implies all dependencies in F. | |||
The set <math>F_c</math> has two important properties: | |||
# No functional dependency in <math>F_c</math> contains an extraneous attribute. | |||
# Each left side of a functional dependency in <math>F_c</math> is unique. That is, there are no two dependencies <math>a \to b</math> and <math>c \to d</math> in <math>F_c</math> such that <math>a = c</math>. | |||
== Algorithm for computing a canonical cover <ref>''Database system concepts'' by Abraham Silberschatz et al</ref>== | |||
# <math>F_c = F</math> | |||
# Repeat: | |||
## Use the union rule to replace any dependencies in <math>F_c</math> of the form <math>a \to b</math> and <math>a \to d</math> with <math>a \to bd</math>. | |||
## Find a functional dependency in <math>F_c</math> with an extraneous attribute and delete it from <math>F_c</math> | |||
# ... until <math>F_c</math> does not change | |||
== References == | |||
{{reflist}} | |||
[[Category:Database theory]] | |||
[[Category:Mathematical concepts]] | |||
[[Category:Algorithms and data structures]] |
Revision as of 01:26, 16 January 2014
A canonical cover for F (a set of functional dependencies on a relation scheme) is a set of dependencies such that F logically implies all dependencies in , and logically implies all dependencies in F.
The set has two important properties:
- No functional dependency in contains an extraneous attribute.
- Each left side of a functional dependency in is unique. That is, there are no two dependencies and in such that .
Algorithm for computing a canonical cover [1]
References
43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.
- ↑ Database system concepts by Abraham Silberschatz et al