Practice Questions Functional Dependency

Duration: 2 min

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This video teaches verifying functional dependencies using relation instances. The instructor works through three examples, guiding viewers to inspect tuples for validity. The first example uses attributes A, B, and C to test single-attribute dependencies. The second uses X, Y, and Z for composite and single dependencies. The final example asks students to identify the single invalid dependency among four choices for a table with five attributes, reinforcing the concept of uniqueness.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor begins by displaying a relation instance with columns A, B, and C containing five tuples. He systematically evaluates a list of functional dependencies: A->B, B->C, B->A, C->B, C->A, and A->C. He places checkmarks and crosses next to each option to indicate validity. Subsequently, he transitions to a new problem involving a relation with columns X, Y, and Z. He analyzes dependencies including XZ->X, XY->Z, Z->Y, Y->Z, and XZ->Y. He marks XZ->X and XY->Z as valid, while crossing out Z->Y (where Z=3 maps to Y=4,5,6) and XZ->Y (where X=1, Z=3 maps to Y=4,5).

  2. 2:00 – 2:07 02:00-02:07

    The video concludes with a multiple-choice question asking to identify the dependency that does not hold good for a relation with columns A, B, C, D, and E. The options are A->BC, DE->C, C->DE, and BC->A. The instructor verifies the validity of the first, second, and fourth options, marking them with checks. He identifies C->DE as the invalid dependency because the value '3' in column C corresponds to different values in columns D and E (specifically D=4,6 and E=5,6), and marks it with an X.

The lecture effectively bridges theoretical concepts of functional dependencies with practical data inspection. By walking through concrete examples, the instructor demonstrates that a dependency X->Y holds only if every unique value of X is associated with exactly one value of Y across all tuples. The progression from simple single-attribute checks to identifying the specific invalid dependency in a complex table reinforces the logical rules of database normalization.