# Database [3i Infotech Placement]: Sample Questions 128 - 129 of 294

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## Question 128

Database
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### Describe in Detail

Essay▾

What are Armstrong rules? How do we say that they are complete and/or sound

### Explanation

• Armstrong՚s Axioms is a set of rules.
• Provides a simple technique for reasoning about functional dependencies.
• Used to infer all the functional dependencies on a relational database.

The well-known inference rules for FD

• Reflexivity:
• If A is a set of attributes and B is a subset of A, then A holds B.
• Augmentation
• If A hold B and C is a set of attributes, then AC holds BC.
• It means that attribute in dependencies does not change the basic dependencies.
• Transitivity
• If A holds B and B holds C, then A holds C.
• If then
• A hold means that A functionally determines B.
• Union
• If A holds B and A holds C, then A holds BC.
• If and
• Pseudo Transitivity
• If A holds B and BC holds D, then AC holds D.
• If
• First three are known as Amstrong Rules.
• They are sound because it is enough if a set of FDs satisfy these three. They are called complete because using these three rules we can generate the rest all inference rules

Database
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