Association submodels

Association submodels are used to contain properties of relationships between one or more other submodels. If only one submodel is involved, the relationship is between different instances of the submodel. If there are two submodels, the relationships are between the instances of the two submodels. An association submodel (which looks just like a normal submodel) is used to contain elements that are held in common between the submodel instances taking part in the association. In effect, these elements do not belong to just one or other submodel but to both. For instance, the concept of a salary requires an employer paying the salary as well as the employee receiving it.

Association submodels are often used to represent a model concisely that otherwise would require repetition. If you are familiar with object-oriented programming, you will notice that association submodels are similar in concept to association classes.

For more information:

• please see the "Introduction to the association submodel concept".
• See also the 3rd video in the Simile Tutorial Series.

Terminology

A 'base submodel' is a submodel that takes part in an association.

A 'relation' is an association between instances of the same base model.

A 'role' is the arrow that connects a base submodel to an association.

To create an association submodel:

1. Create one or more multiple instance submodels that will be associated, each playing a role in the association. These are the base submodels.
2. Create unique identifying variables in the base submodels. The variables allow unique identification of an instance. This is easy to specify, using variables taking the value of the submodel index (or indices).
3. Create a single instance submodel which will be the association submodel itself, containing variables that specify the association.
4. Draw role arrows from the base submodels to the association submodel. The role arrows should be given meaningful names indicating the role the instances of the base submodel play in the association. Meaningful role names make specifying the equations in the association much easier.
5. Add a condition symbol in the association submodel specifying when the association holds true. The condition is an expression involving the identity variables of the base submodels.
6. Include in the association submodel all the variables that belong equally to all base submodels.
7. Draw influences between relevant variables in associated submodels and the association submodel and specify these variable's equations.

To follow this in practice:

• please see the "Worked example: water flow between soil layers".

Note that there are some advanced aspects of optimising the performance of models using associations For more information please see:

• Role arrow properties dialogue box
• One-sided relationship enumeration

In: Contents >> Working with submodels