Database concepts

Topics: Database normalization, Relational model, Database Pages: 3 (586 words) Published: July 30, 2014

Assignments Requirements
1.Look up the definition of functional dependency. Can you find a good example? In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database. Cars

Suppose one is designing a system to track vehicles and the capacity of their engines. Each vehicle has a unique vehicle identification number (VIN). One would write VIN → Engine Capacity because it would be inappropriate for a vehicle's engine to have more than one capacity. (Assuming , in this case, that vehicles only have one engine.) Transversely, Engine Capacity → VIN is incorrect because there could be many vehicles with the same engine capacity. This functional dependency may suggest that the attribute Engine Capacity be placed in a relation with candidate key VIN. However, that may not always be appropriate. For example, if that functional dependency occurs as a result of the transitive functional dependencies VIN → Vehicl e Model and Vehicle Model → Engine Capacity then that would not result in a normalized relation. http://en.wikipedia.org/wiki/Transitive_dependency

2.Look up the definition of transitive dependency. Can you find a good example? In Database Management System, a transitive dependency is a functional dependency which holds by virtue of transitivity. A transitive dependency can occur only in a relation that has three or more attributes. Let A, B, and C designate three distinct attributes (or distinct collections of attributes) in the relation. Suppose all three of the following conditions hold: 1.A → B

2.It is not the case that B → A
3.B → C
Then the functional dependency A → C (which follows from 1 and 3 by the axiom of transitivity) is a transitive dependency. In database normalization, one of the important features of third normal form is that it excludes certain types of transitive dependencies. E.F. Codd, the inventor of the relational model, introduced the concepts of transitive...
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