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ER diagram: employee, skill, machine

Short answer

Entities: Employee (emp_id, name, address), Skill (skill_id, skill_name), Machine_type (type_id, type_name). Relationships: Employee possess Skill (M:1), Employee operates Machine_type (M:1), Employee maintains Machine_type, Skill needed to operate Machine_type (1:1).

Draw an ER diagram for the following. [The question text is not printed; the page gives only the label and the solution diagram: employee possess skill (M:1); employee operates machine_type (M:1); employee maintains machine_type; skill is needed to operate machine_type (1:1).]

The question gives the entities (employee, skill, machine_type) and four relationships with their cardinalities. The attributes below are assumed.

Entities and attributes

  • Employee (emp_id, name, address): primary key emp_id.
  • Skill (skill_id, skill_name).
  • Machine_type (type_id, type_name).

Relationships

RelationshipBetweenCardinality
possessEmployee - SkillM : 1
operatesEmployee - Machine_typeM : 1
maintainsEmployee - Machine_type(as drawn in the solution, no ratio shown)
is needed to operateSkill - Machine_type1 : 1

ER diagram

              M                    1
 [Employee]=======<possess>=======[Skill]
   |   |                              |
   |   | M                            | 1
   |   +----<operates>---+            |
   |                     | 1     <needed_to_operate>
   |                     |            |
   |    <maintains>      |            | 1
   +---------------------+---[Machine_type]

Here the rule "skill is needed to operate machine_type" is 1 : 1: one skill is required for exactly one machine type. Employee operates one machine type (M : 1), so many employees may operate the same type. Maintains is a separate relationship between the same two entities, so it needs its own diamond.

✓ Answer checked by Claude Opus 5.5 (high effort)

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