# Towards Agent Organizations Interoperability: A Model Driven Engineering Approach
## 4 Abstract Conceptual Structure of Organizational Models
### Structural Dimension
#### 4.2.2 Particularities  
Besides the similarities that give rise to the structural specification pattern, the organizational models also differ in some particular points. Four of these points deserve mention. The first one is related to the definition of subgroups. In STEAM and MOISE+, the definition of subgroups forms a real hierarchy, i.e., an non cyclic graph. On the other hand, in AGR and OPERA, there is no explicit subgroup relationships between group definitions. From structural specification pattern perspective, this fact can be expressed in the following way: In AGR and OPERA, for each group definition g (instance of GroupDef), the collection of its subgroups is empty, i.e., g.subGroup = {}. On the other hand, in STEAM and MOISE+, there exist group definitions g such that g.subGroup \(\
eq\) {}. The second point is the notion of _cardinality_ that is found in AGR and MOISE+ but not in the other models. Cardinalities can be defined for roles or subgroups. In the case of roles, cardinalities indicate a maximum and a minimum number of agents allowed per role in the context of a group. Regarding cardinalities of groups, they determine how many subgroups of a given type can be created in the context of a group. In AGR, cardinalities are attributes of role and group. In MOISE+, they are attributes of the association between role and group, or group and subgroup. For this reason, and observing that they are not an explicitly feature of the majority of the models, we have chosen not to explicitly represent cardinalities in the structural specification pattern. As third point, we observe that the abstract notion of _structural relationships between roles_ (class RoleRel, Table 4) admits diverse concrete subtypes, analogously to what happens with the notion of _goal relationships_ (class RoleRel, Table 2). In AGR, for instance, there exist two subtypes: _Correspondence_ (which states that agents playing one role will automatically play another one) and _dependency_ (which rules out the possibility of an agent to play one role if it is not playing another role). In MOISE+, three subtypes: _Links_ (which declare the possible relationships of _communication_, _authority_ and _acquaintance_ between roles), _compatibility_ (which determines that two roles can be played at the same time by the same agent) and _inheritance_ (which states that one role, besides its own features, also has all the features, like links and compatibilities, of another role). In ISLANDER, two subtypes: The concept of _subroles_ (which is similar to the concept of inheritance in MOISE+), and the concept of _static separation of duties_ (which means the opposite of the concept of _compatibility_ in MOISE+). In OPERA, there is only one type of binary directed relationship between roles: The _dependency_. Nevertheless, differently from the other organizational models, the concept of _dependency between roles_ in OPERA is not properly a structural but rather a functional relationship. In other words, in OPERA, the dependency relationship reflects directly the decomposition of a goal into subgoals, elements of the functional dimension. When one of the subgoals defined in the scope of a role is a goal of another role, then there exist the dependency relationship between the two roles in OPERA. Such idea is different from the structural dependency present in AGR, which indicates that the fact of playing a given role is a prerequisite for playing another role. The last point that should be mentioned concerns the nature of the group definitions. In all analysed models, except MOISE+, agents playing any roles in the same group may, in principle, exchange messages. Further, in the absence of explicit constraints, such as incompatibilities or dependencies, the agents are free to play the roles they wish in a given group. In MOISE+, we have the opposite situation. If there is no explicitly stated communications links or compatibility relations between roles, the agents are not allowed to exchange messages or play more than one role in the same group.