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Chapter 10: Problem 6

Why can we not infer a functional dependency automatically from a particular relation state?

Short Answer

Expert verified
Functional dependencies cannot be inferred automatically from a specific relation state because they are a property of the attribute's semantics and relationships, not of individual instances of the database. A particular relation state at a specific point in time might not reveal all functional dependencies as it is a snapshot of the database at a given moment.

Step by step solution

01

Understanding Functional Dependencies

Functional dependency is a key concept in normalization in a database. It is a set of constraints between two attributes in a relation. Functionally dependent means the value of one attribute (the determinant) determines the value of other attributes. However, a functional dependency is a semantic constraint and not a syntactic one. In fact, it is a property of the attribute's semantics and the relationship among attributes.
02

Exploring Relation States

A relation state refers to a specific instance of a database at a particular point in time. It represents the data in a database at a specific moment. It's important to remember that relation states can change as records are added, altered, or deleted from the database.
03

Why We Can't Infer Functional Dependency from Relation States

Functional dependencies are based on the semantics and relationships of the attributes, not on individual instances of a database. Hence, inferring functional dependencies from a specific relation state could be misleading. Because the state of the database changes over time, at a specific point in time, it might not reveal all functional dependencies. A relation state represents a snapshot in time, and it might either not contain all possible data combinations or contain incorrect data. Thus, it might lead to the wrong deduction of functional dependencies.

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Most popular questions from this chapter

When are two sets of functional dependencies equivalent? How can we determine their equivalence?

Consider the following two sets of functional dependencies: \(F=\\{A \rightarrow C, A C \rightarrow\) \(D, E \rightarrow A D, E \rightarrow H\\}\) and \(G=\\{A \rightarrow C D, E \rightarrow A H\\} .\) Check whether they are equivalent.

Discuss attribute semantics as an informal measure of goodness for a relation schema.

What does the term unnormalized relation refer to? How did the normal forms develop historically from first normal form up to Boyce-Codd normal form?

Discuss insertion, deletion, and modification anomalies. Why are they considered bad? Illustrate with examples.
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