Pattern and Meta-Pattern

Meta-language representation for patterns

In order to have a process that starting from the model of a pattern can generate its multi-platform implementations, we adopt several intermediate representation as shown in fig. 5. Starting from the UML description we obtain the XML meta-pattern (that is platform independent); from this, applying an XSLT transformation, we deduct the platform (FIPA-OS or JADE) specific pattern. With another transformation that introduces some of the implementation features of the platform we construct the JAVA skeleton. At this skeleton we add the body of the methods (when available for the specific environment) obtaining a class that is complete both in the structure and in the inner code.

Fig. 1

More in details we can note that each pattern is represented at design level with two different kind of diagrams (structural and behavioral). In fig. 6 we can see the design representation of the pattern. This allows (together with a complete textual documentation including the goal addressed by the pattern) to the designer the choice of the correct element he could need. Now we will discuss the process that starting from this model brings to the code of the agents in the different implementation environments.

Fig. 2

As already discussed, in our work we refer to FIPA-compliant platforms and specifically to the FIPA-OS and Jade frameworks. As both of them present agent structures as classes containing attributes, methods and inner-classes, we thought to adopt a hierarchical meta-language to describe the agent and his properties. The hierarchy’s root level entity is the agent, which contains inherent properties such as attributes, methods and tasks (the inner classes). We have chosen XML as our meta-language as it is oriented to tree data structure representations. It proved very useful for managing agents and tasks. As a matter of fact, this allowed us to easily manipulate their structure and add, edit or delete agents’ properties very easily. This is the key point in the application of a pattern to an existing agent in terms of skills and behaviors. We believe that the use of a meta-language can give us a straight way to create and maintain a repository of patterns. Moreover, agents’ source code can be automatically generated from meta-language representation without any manual support.

The choice of XML is also valid in the context of the Agent Factory Project that we are carrying on and that has been funded by the AgentCities.NET initiative. As a matter of fact, because of the XML easy portability, agents’ patterns will be shared in a web server, so that designers of the Agentcities community will be able to access and update them.