Module 3
Schema Refinement
Guidelines for Relational Schema
Functional Dependency
Normalization
Guidelines for Relational Schema
Semantics of the attributes is clear
Reduce data redundancy and update
Anomalies
Update Anomalies
Insertion Anamolies
Modification Anamolies
Deletion Anamolies
Reduce NULL values – Join operation may provide null values
Avoid spurious tuples – Extra rows due to faulty join operations
Functional Dependency
A functional dependency (FD) is a constraint between two set of attributes from the
database.
Trivial Functional dependency
X -> Y is a trivial functional dependency if Y is a
subset of X
Non Trivial Functional dependency
X -> Y is a Non trivial functional dependency if Y is
not a subset of X
Benefits of Functional Dependency
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Avoids data redundancy
Ensures the quality of data in the database
Defined meanings and constraints of databases
Identify bad designs
Normalization
• Normalization is the process of minimizing data
• redundancy and modification anomalies
• Normalization is a part of good database design
• Pitfalls of DB
• Data redundancy
• Repeating groups
• Modification anomalies
• Insert, Update, Delete