ER Model, Keys and Integrity Constraints Notes for GATE DA: Concepts, Formulas, Worked Examples & Practice

    ER Model, Keys and Integrity Constraints notes for GATE DA: 20 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice questions.

    Chapter Roadmap: ER Model, Keys and Integrity

    Chapter Roadmap

    ER Model, Keys and Integrity Constraints

    This chapter bridges the gap between how we visualize data and how we actually store it. By the end, you will master the translation of conceptual designs into robust logical schemas.

    Topic 1 - Current
    ER-to-Relational Mapping
    Transform ER diagrams into relations. Handle multivalued attributes, weak entities, and complex relationships. (Moderate Weightage)
    Topic 2
    Keys & Foreign Key Integrity
    Master primary, candidate, and super keys. Understand referential integrity, ON DELETE/UPDATE actions, and NULL handling. (High Weightage)

    ER-to-Relational Mapping and Multivalued Attributes

    ER-to-Relational Mapping

    Bridge the gap between conceptual design and logical implementation.

    Strong & Weak Entities:
    Flattening composites and inheriting keys.
    Binary Relationships:
    1:1, 1:N, and M:N mapping rules.
    Multivalued Attributes:
    Achieving First Normal Form through separate relations.
    n-ary Relationships:
    Handling complex multi-entity associations.

    Mapping Strong and Weak Entities

    Mapping Strong and Weak Entities

    Mapping Strong Entities
    • Becomes a relation with the same name.
    • Simple attributes become columns.
    • Primary key becomes the relation's primary key.
    • Composite attributes are flattened into their constituent simple attributes.
    Mapping Weak Entities
    • Becomes a relation.
    • Includes all its simple attributes.
    • Includes the primary key of its owner (strong entity) as a foreign key.
    • The primary key of this new relation is the combination of the owner's primary key and the weak entity's discriminator (partial key).

    Mapping Binary Relationships: 1:N and M:N

    Mapping Binary Relationships: 1:N and M:N

    Relationship Type Mapping Rule
    1:N (One-to-Many) Do not create a new relation. Add the primary key of the '1' side as a foreign key in the relation of the 'N' side. Include any descriptive attributes in the 'N' side relation.
    M:N (Many-to-Many) Create a brand new relation. Include any descriptive attributes. The primary key is the combination of the primary keys from both participating entities.

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    ER Model, Keys and Integrity Constraints Notes for GATE DA: Concepts, Formulas, Worked Examples & Practice

    ER Model, Keys and Integrity Constraints notes for GATE DA: 20 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice questio

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