Assigner

An assigner state model arbitrates competition for instances across a relationship.

There are two kinds of assigner, single and multiple.

The elevator example has only one assigner which happens to be multiple, so let's take a look at that one.

Multiple assigner

The declaration line looks like this:

relationship R53 / Shaft

And the grammar is:

assigner = "relationship" SP rnum (SP '/' SP name)? EOL*
rnum = r'O?R[1-9][0-9]*' // Relationship number

Reading it left to right: the keyword relationship, one space, the relationship number and in the case of a multiple assigner, one space, a slash, one space, and then a partitioning class name.

An assigner may only be defined on an association relationship, one with or without an association class. If you try to define an assigner state model on a generalization or an ordinal, the parser won't stop you, but you won't be able to populate it in the metamodel.

The / Shaft component indicates that competition is local to each Shaft instance. Transfer requests for a Cabin in Shaft S1, for example, don't compete with requests for a Cabin in Shaft S2. Thus there are multiple assigner mediators on the association, one per instance of Shaft. We refer to Shaft as the partitioning class.

Single assigner

For a single assigner, there is no partitioning class. So you would just see a line like:

relationship R302

No partitioning class is specified.