IPA FE Subject A 2025 Question 11
A question IPA Japan published in 令和７年度 基本情報技術者試験 科目A 公開問題 問11, translated into English. ITPEC is based on the same exams.
Which of the following is a characteristic of an entity in the E-R model?
Explanation
An entity has attributes that represent its characteristics — in the E-R model an entity is a kind of thing the business keeps data about, described by its attributes.
An entity such as Customer or Order is described by attributes such as customer number, name and address. Each concrete occurrence, one particular customer, is an instance of the entity, and relationships connect entities with a cardinality such as one-to-many. When the model becomes a relational database, an entity usually becomes a table and its attributes its columns.
Answer (c)
Why not others:
- •(a) — one entity has many instances (Customer has one instance per customer), so the correspondence is one-to-many, not one-to-one
- •(b) — entities need not be physical; intangible things such as an order, a contract or a reservation are entities too
- •(d) — relationships between entities are expressed as associations with a cardinality (one-to-one, one-to-many, many-to-many); state transitions are drawn in a state transition diagram
Key rule: In an E-R model an entity is a kind of thing, tangible or not, described by attributes; an instance is one occurrence of it; a relationship is an association between entities with a cardinality.
Databases · AI-written, may contain errors
This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.