7 Integrating ZEUS Agents with External Programs

The preceding sections have mentioned the primary interfaces between ZEUS agents and external programs. These include the domain functions in primitive plan operator specifications, and user-defined Co-ordination Engine graphs whose nodes make direct calls to external programs.  Also mentioned was the fact that the Resource Database implements an interface that could be used, for example, with the database connectivity API of Java to link to proprietary databases – thus extending its potential size and functionality.  For routine problem solving within the declared scope of the ZEUS toolkit, it is expected that for the most part, these primary mechanisms will suffice.  However, the Agent Component Library also provides a secondary, more sophisticated interface, although employing it requires significant user programming. This done via a ZeusExternal interface class and an agent internal event model.

The ZeusExternal interface class allows users to link an external Java class (that implements the interface) to an executing ZEUS agent program.  Once linked to the agent program, the external code can utilise the agent’s public methods to query or modify the agent’s internal state.  Thus, for example, the resource and/or plan databases can be queried or modified.

The TaskExternal interface class performs a similar function, to allows users to link an external Java class that implements the activity of a Zeus task. This interface also contains references to its owner agent, enabling the task to query or change its internal state.

The internal event model provides a mechanism whereby all significant events occurring in the agent can be monitored, e.g. planning events, resource, acquaintance and plan database events, message events, execution monitor events, and co-ordination engine events.  The internal event model is similar to the Java event model, whereby objects register an interest in receiving events of a particular type, and all subsequent events of that type are forwarded to the object.  So, using the event model, an external program that is linked to a ZEUS agent can monitor particular events in the agent and react to them, even by going so far as to use the agent’s public methods to make changes to its internal state.  Although the reader is forewarned that ZEUS currently does not even attempt to manage any internal inconsistencies that might result from such actions.

The ZEUS Application Realisation guide provides several examples of how to use the event model.

Concluding Remarks

The purpose of this document has been to explain the philosophy and functionality that underly the ZEUS toolkit. In particular, the way in which the agent-level issues are encapsulated inside agent components, separate from application-level issues. This is deliberate, to enable developers to create working multi-agent systems more easily and efficiently. If others can use Zeus to build their own applications, our decision to employ a declarative specification of behaviour that is interpreted by the generic ZEUS agent will have been vindicated.

Although this document provides an insight into how agent applications can be built from the toolkit components, it has deliberately avoided discussing how agent applications should be designed.  There is also no description of how tools such as the ZEUS Agent Generator tool can be used to create executable applications.  Instead, these are subjects dealt with in the ZEUS Methodology documents.