Contents
What is the minimal cover of a set of functional dependencies?
= ABCD. We say that a set of functional dependencies F covers another set of func- tional dependencies G, if every functional dependency in G can be inferred from F. More formally, F covers G if G+ ⊆ F+. F is a minimal cover of G if F is the smallest set of functional dependencies that cover G.
Is minimal cover unique?
Minimal covers are not unique: for 3NF design we use a particular kind of minimal cover, called a canonical cover. Canonical covers are computed as follows: Decompose fds into non-trivial fds that have only one attribute at the right side.
Is minimum cover unique?
What is a minimal basis?
Given a set F of FDs, a minimal basis is a set G of FDs for which: Every FD in G has just one attribute on its right side. For any FD from G , removing an attribute from its left side results in a set of FDs that is not a basis for F .
Which is an example of a minimal cover?
Minimal cover (example discussed in class) F = { AB -> C, C -> A, BC -> D, ACD -> B, D -> E, D -> G, BE -> C, CG -> B, CG -> D, CE -> A, CE -> G} Notice that we have single attribute on the RHS in all FDs, we need to look for extraneous (redundant) attributes on the LHS and also look for FDs that are redundant.
How to create minimal cover in a database?
Simple properties/steps of minimal cover: 1 Right Hand Side (RHS) of all FDs should be single attribute. 2 Remove extraneous attributes. [ What is extraneous attribute? 3 Eliminate redundant functional dependencies.
How to find minimal cover of set of functional dependencies?
A set of FDs F is minimum if F has as few FDs as any equivalent set of FDs. [ How to find minimal cover? – Refer here]. 1. Right Hand Side (RHS) of all FDs should be single attribute.
How to get a minimal cover in Java?
To get the minimal cover, you have to make two steps. To demonstrate, I’ll first split the dependencies into multiple (only one attribute on the right side) to make it more clean: The following steps must be done in this order (#1 and then #2), otherwise you can get incorrect result.