ERD:

Scenario:

The above ERD represents the details of a simple course database which records the course registration details of students. The course entity has a unique identifier CourseNum and the Registration entity is allocated a partial key. The mode represents the mode of registration: online or on-campus. A student may have more than one phone number.

Semantic Rules:

1. Each course may have many registrations.
2. Many registrations are recorded for each course.
2. Each student may register only once.
2. Each student can have multiple registrations.

Question: What type of entity is Registration?

Question

ERD:

Scenario:

The above ERD represents the details of a simple course database which records the course registration details of students. The course entity has a unique identifier CourseNum and the Registration entity is allocated a partial key. The mode represents the mode of registration: online or on-campus. A student may have more than one phone number.

Semantic Rules:

1. Each course may have many registrations.
2. Many registrations are recorded for each course.
2. Each student may register only once.
2. Each student can have multiple registrations.

Question: What type of entity is Registration?

BlackTom AI · Accepted Answer

Question restatement: What type of entity is Registration? Options: 1) Weak Entity 2) Partial Entity 3) Associative Entity 4) Strong Entity.

Option 1: Weak Entity. This is the plausible choice because the Registration entity is described as being allocated a partial key. In ER modeling, a weak entity has no complete primary key of its own and relies on a relationship to an owner entity to provide its identifying key, typically using a partial key combined with the owner's key. The diagram shows Registration linked to Course with an identifying relationship, and Registration includes a partial key, which aligns with the characteristics of a weak entity. The semantics also fit: there can be many registrations for a course, and a student can have multiple registrations, suggesting Registration depends on Course (and possibly Student) for its identity.

Option 2: Partial Entity. This term is not standard in ER modeling. While a partial key is a feature of a weak entity, the phrase Partial Entity does not describe a recognized benign category of entity type in classical ER modeling. Therefore, labeling Registration as a Partial Entity would be inappropriate and misleading.

Option 3: Associative Entity. An associative (or bridge) entity is used to model many-to-many relationships between two entities by turning the relationship into its own entity with its own attributes. In this scenario, the depicted relationships and semantic rules do not indicate that Registration is resolving a many-to-many between two entities; instead, Registration appears to be a dependent entity with a partial key, not simply a connector for a many-to-many relationship. Thus, calling Registration an associative entity would misrepresent its role.

Option 4: Strong Entity. A strong (or regular) entity has its own complete primary key and does not rely on another entity for identity. Since Registration is described as having a partial key, and appears to be existence-dependent on the owning context (course, possibly student) for identification, it does not fit the definition of a strong entity. Therefore, this option is inconsistent with the given details.

In summary, the presence of a partial key and the depiction of Registration as dependent on another entity for its identity best align with the concept of a weak entity, while the other options conflict with the provided clues or standard terminology.

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