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Functional Dependencies

On starting the tutorial, we straight away go to the Functional Dependecies section. The definations are given for the functional dependencies, with concise examples and important uses and aspects of FD.

Figure 3.1: FD's definition

The Armstrong Axiom system is introduced, with the inference rules, which are used to derive functional dependencies, with various examples.

Figure 3.2: Armstrog Axiom System

Next we introduce the functional dependencies, in our current system.

Figure 3.3: FD's in our System

The system also describe the keys and superkeys, which are esential for the functional dependencies.

Figure 3.4: Keys and SuperKeys

These functional dependencies are used to normalize the database, so we give of the ultimate normal form called Boyce Codd Normal Form (BCNF).

Figure 3.5: BCNF Definition

The star of the tutorial is the BCNF varification applet.In this program, user can build up a relation with specifying its attributes and some functional dependencies holding on the relation can also be designed by the user. After designof relation schema, the user can perform verification on the relation to check whether the relation is in BCNF.

Figure 3.6: Example Relation in BCNF

First of all, the relation attributes and functional dependencies over the relation should be inputted. The inserted item would display in corresponding textbox after pressing 'Add' button. And the specified item also can be deleted by pressing 'Remove' button. If the designed relation is ready, user can click the button, 'Verify BCNF' to start to verify the designed relation whether is in BCNF or not.

Figure 3.7: Example Relation not in BCNF

Khan Samee Ullah
Wed Dec 19 10:09:47 CST 2001