Condition

A condition model element is used to specify whether a submodel, or a potential instance of a multiple-instance submodel, actually exists.

How to add a Condition symbol

The condition symbol only has meaning inside a submodel. Therefore, you should make the submodel first, then add the condition symbol to it. This is not strictly necessary: you can add the condition symbol first, then construct a submodel around it, but it is better practice to construct the submodel first.

See Adding node-type elements.

Rules

• A condition element only has use within a submodel (since it specifies which potential instances exist). It should not appear in a population or per-record submodel because these have their own means of creating and destroying instances.

• The expression in the equation dialogue box for a condition element is a Boolean expression: that is, it returns the value "true" or "false". This normally takes the form of some sort of comparison, using the conditional operators such as >, <, >= etc, combined with logical operators such as "and" and "or". However, conditions of the form "index(1) is <expr>" or "any(index(1) is <list_expr>)" are also allowed; see one-sided relation enumeration.

• If a condition is inside a simple submodel, then that submodel either exists or not, depending on the result of evaluating the condition's expression.

• If a condition is inside a fixed-membership submodel, then each instance of the submodel may exist or not, depending on the condition's expression (which would make use of the built-in function index to refer to particular instances).

• If the condition model element is inside an association submodel, then the relation exists between a particular pair of object instances only if the condition's expression evaluates to "true" for that pair.

In : Contents >> Model diagram elements