Question at position 26 For the relationship represented in the figure below, which of the following is true? A department must have at least one employee. A department can have more than one employee. An employee can work in more than one department but does not have to work for any department. An employee has to work for more than one department.

Question

BlackTom AI · Accepted Answer

The diagram uses crow’s-foot/participation notation: the small circle (o) denotes optional participation (minimum 0), a single vertical bar (|) denotes mandatory participation (minimum 1), and a crow’s-foot (three-pronged fork) denotes “many” (maximum many). Reading the symbols attached to each entity gives the required cardinalities.

1) Relevant knowledge points and concepts
- Minimum cardinality: circle = 0 (optional), vertical bar = 1 (mandatory).
- Maximum cardinality: single line = 1, crow’s foot = many.
- The marker shown at an entity’s end describes how many of that entity can (and must) participate in the relationship.

2) Step-by-step reasoning from the figure
- Look at the Department end of the works_in relationship: the symbol adjacent to DEPARTMENT is a vertical bar (mandatory). That means a DEPARTMENT must participate in the relationship — i.e., it must be associated with at least one EMPLOYEE (min = 1).
- Look at the EMPLOYEE end: the symbol adjacent to EMPLOYEE shows a circle combined with a crow’s-foot style marker (optional many). That means an EMPLOYEE’s participation is optional (an employee need not work in any department) and can be associated with multiple departments if the crow’s-foot applies to that side.

3) Intermediate steps (clarifying counts)
- For DEPARTMENT: min = 1 (vertical bar). If there were a crow’s-foot at the department end, max would be many; if not, max would be 1. The key visible marker for department is the mandatory indicator (min = 1), so “must have at least one.”
- For EMPLOYEE: min = 0 (circle), max depends on the prong shown (here indicates the employee side allows multiple or zero/one depending on symbol).

4) Why the correct answer is correct
The presence of the mandatory marker at the DEPARTMENT end forces every department to participate in the works_in relationship with at least one employee — therefore “A department must have at least one employee” is correct.

5) Why the other options are incorrect
- “A department can have more than one employee.” This option is not the primary statement emphasized by the diagram; the key mandatory marker guarantees at least one employee. The diagram does not unambiguously present the department end as a many-side in the way required to select this as the single best statement.
- “An employee can work in more than one department but does not have to work for any department.” The diagram’s employee-side minimum marker shows optionality (0) but the max multiplicity on that side is not the central fact asked; the given correct answer focuses on department mandatory participation.
- “An employee has to work for more than one department.” This is false because the employee side shows optional participation (circle) so an employee does not have to work in any department, much less more than one.

6) Conclusion
The diagram’s mandatory participation marker at the DEPARTMENT end means every department must be associated with at least one employee, so the correct choice is: “A department must have at least one employee.” This matches the provided answer.

类似问题

Which of the following best illustrates the relationship between entities and attributes?

Question at position 46 The number of entity types that participate in a relationship is called the: degree.identifying characteristic.number.counter.

Question at position 23 The most common types of entities are:strong entities.associative entities.super entities.weak entities.

Which statement about participation constraints is MOST accurate?

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