Entity-Relationship Modeling Flashcards
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Read the first 7 Entity-Relationship Modeling flashcards as text
When mapping a many-to-many (M:N) binary relationship to relational tables, the correct approach is to:
Answer: Create a new junction table with foreign keys referencing both entity tables
An M:N relationship requires a junction (cross-reference) table whose composite primary key consists of the primary keys of both participating entities.
Which of the following best describes 'cardinality ratio' in an ER relationship?
Answer: The maximum number of relationship instances in which an entity instance can participate
Cardinality ratio (1:1, 1:N, M:N) specifies the maximum number of relationship instances an entity can participate in on each side.
What is the purpose of a 'surrogate key' in a relational table derived from an ER model?
Answer: To provide a system-generated, artificial primary key when no suitable natural key exists
A surrogate key is a system-generated identifier (often an auto-incremented integer) used when a natural primary key is unavailable or impractical.
In an ER diagram, a multivalued attribute is depicted as:
Answer: A double ellipse
A double ellipse represents a multivalued attribute, indicating that an entity instance can have multiple values for that attribute.
When a multivalued attribute is converted to a relational schema, the standard practice is to:
Answer: Create a separate table for the multivalued attribute with a foreign key referencing the original entity
To maintain 1NF, a multivalued attribute is placed in its own relation (table) that references the owning entity via a foreign key.
Which scenario best illustrates a 'total participation' constraint?
Answer: Every employee must be assigned to at least one department
Total participation means every entity instance must participate in the relationship, so every employee is required to belong to a department.
An ER model is typically created during which phase of the database development lifecycle?
Answer: Conceptual design phase
ER models are produced during the conceptual design phase, before physical or logical schema details are determined.