In transforming an entity–relationship (ER) model to a relational schema, is it correct that each entity type is represented as a separate table (with relationships mapped via keys or associative tables)?
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ACorrect
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BIncorrect
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COnly weak entities become tables
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DOnly supertype entities become tables
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EEntities become views, not tables
Answer
Correct Answer: Correct
Explanation
Introduction / Context:Logical design converts an ER model into a relational schema. A core rule is that each entity type becomes a table (relation), while relationships are enforced with foreign keys or separate intersection (associative) tables for many-to-many links.
Given Data / Assumptions:
- Standard ER-to-relational mapping is being applied.
- Attributes of entities become columns in the corresponding table.
- Identifiers (primary keys) are chosen as natural or surrogate keys.
Concept / Approach:Every entity type (strong or weak) maps to a table. One-to-many relationships become foreign keys in the “many” side. Many-to-many relationships become separate intersection tables with foreign keys to both parents. Subtype/supertype hierarchies map via one of several patterns (single table, class table, or concrete table inheritance). The statement focuses on entities, and that mapping is correct.
Step-by-Step Solution:
Identify entity types in the ERD.Create tables for each entity; move attributes to columns.Define primary keys and necessary unique constraints.Map relationships with foreign keys or intersection tables as needed.Verification / Alternative check:Compare the resulting schema to the ERD: counts of entity types should match counts of core tables (excluding associative tables introduced for M:N relationships).
Why Other Options Are Wrong:
- Restricting to weak or supertype entities ignores standard mapping.
- “Entities become views” is design-specific and not the default mapping rule.
- “Incorrect” contradicts standard methodology.
Common Pitfalls:Forgetting to normalize multi-valued attributes; failing to create intersection tables for M:N; mishandling subtype mapping and keys.
Final Answer:Correct