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Understanding Relationships between Functional Dependencies (FDs) and Entity-Relationship Diagrams (ERDs)

Explore the connection between FDs and ERDs, deriving FDs from ERDs, discussing Intra FDs (entity identifier determines attributes) and Inter FDs (relationships between entities). Learn how to combine FDs based on common LHS. Examples provided.

phailin-suttikul
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Understanding Relationships between Functional Dependencies (FDs) and Entity-Relationship Diagrams (ERDs)

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  1. Relationships among FDs and ERDs. In the previous lectures, we saw that a schema that can be generated from a mapped translation satisfies 3NF. In reverse direction, we can generate all FDs from an ERD. We discuss these FDs from Intra FDs and Inter FDs.

  2. Cont’ (1) Intra FDs: - The identifier of an entity determines all non-key attributes. (2) Inter FDs

  3. Inter FDs Suppose we have a relationship R between entity A and entity B, where whose primary keys are A# and B#. Then, we have the following FDs between two entities, depending on cardinality: (a) 1:1 A# --> B# B# --> A# (b) 1:N B# --> A# (note: A# -/-> B#)

  4. Inter FDs (c) M:N no FDs between A# and B# (note: A# -/-> B# and B# -/-> A# ) Suppose relationship R has an attribute called W. Then, we have: A#B# --> W

  5. Cont’

  6. Intra FDs Pic# -->PicTitle, PicYear PicArtist -->ArtistCountry, ArtistType Museum# -->MuseumName, MuseumAddr

  7. Inter FDs Pic# -->PicArtist, Museum#

  8. Cont’ Thus, we can combine them based on their common LHS. Pic# -->PicTitle, PicYear, PicArtist, Museum# PicArtist -->ArtistCountry, ArtistType Museum# -->MuseumName, MuseumAddr

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