attributes - er モデルのエンティティと属性

Question

簡単な質問:

私はモデルを持っています。私は実体車を持っています。車はBMWでもオペルでも構いません。それがBMWなら、それは色を持っている必要があります. それがオペルの場合、属性 - 乗客の量が必要です。

er モデルではど​​のように表示できますか? つまりIFクラスです。

ありがとう！

Answer 1

In an ER model this is normally represented as a sub-type.

http://en.wikipedia.org/wiki/Enhanced_entity%E2%80%93relationship_model

Sub-types can be exclusive or non-exclusive, depending on whether more than one of the sub-types should apply simultaneously. For example, a Bank Account entity might have sub-types for Current Account or Savings Account. These would be exclusive sub-types since a bank account cannot be both. Depending on the type of the account, one of the sub-types is used to "extend" the main entity. On the other hand an entity named Sportsman could have sub-types Golfer and Footballer. The Sportsman entity would contain common information such as name, and the sub-types would contain only the additional attributes applicable to the sport (e.g. Golf Handicap). Records only exist in the sub-type entities when the main entity is of the applicable type. These would be non-exclusive sub-types since it is quite possible that someone plays both golf and football.

In IDEF1X notation it is represented like this