A reusable expression is a piece of logic that is reused throughout the Blueriq model. We speak of a reusable expression to indicate that the purpose of it is to be reused, in Blueriq Encore this is shortened to expression. Reusable expressions are used when the specific logic element will be used more than once within the model or when it is only used once but the business engineer developing it deems it very likely that it will be used more than once in the future.

Whenever reusable expressions are used, one might also opt to use attributes. The value of the attribute in question is determined by an expression within that attribute (and therefore not reusable) but the attribute is reusable.

Shown below is the same piece of (simple) logic. The age (of an applicant) is determined using his or her date of birth.

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.