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One might argue in favor of using reusable expressions or attributes. Arguments to use one or the other are enumerated below.

1. When the expression is clearly only applicable for one entity, an attribute is favored.
2. When the expression is used in more entity, a reusable expression is favored. However, attributes that use this expression can still be modeled.
3. Remember that not all attributes make sense semantically. The number of persons as an attribute for person makes no sense. If that fact is necessary, perhaps model it as a reusable expression.
4. There are arguments to use control-entities or steering-entities. For example to store the number of persons, as mentioned in the previous item. However, they do not have any semantic advantage.

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