A Methodological Proposal for Multiagent Systems Development extending CommonKADS

Carlos A. Iglesias tex2html_wrap_inline826 gif, Mercedes Garijo tex2html_wrap_inline828 ,
José C. González tex2html_wrap_inline828 and Juan R. Velasco tex2html_wrap_inline828
tex2html_wrap_inline826 Dep. de Teoría de la Señal, Comunicaciones e Ing. Telemática, E.T.S.I. Telecomunicación
Universidad de Valladolid, E-47011 Valladolid, Spain
{cif@tel.uva.es}
tex2html_wrap_inline828 Dep. de Ingeniería de Sistemas Telemáticos, E.T.S.I. Telecomunicación
Universidad Politécnica de Madrid, E-28040 Madrid, Spain
{mga,jcg,juanra}@gsi.dit.upm.es

Abstract:

The application of agent technology to real applications needs the development of a methodology which support all the software development life cycle (SDLC) of an agent based system including its management. This paper proposes an extension of CommonKADS for fitting the characteristics of the agent approach in the SDLC and the definition of a new model, the coordination model, for describing the coordination protocols.

The need of a methodology

Despite the great interest around the agent technology in the scientific community, and the introduction of terms such as Agent-Based Software Engineering [Wooldridge & Fisher, 1994] and Multi-Agent Systems engineering [Müller, 1996], there has been little work for defining a methodology for designing agents and agent based systems as pointed out in [Jennings, 1995, Jennings & Wooldridge, 1995, Müller, 1996].

Here it is presented a first approach to the definition of a general methodology for multiagent systems (MAS), which has been developed because of the need of applying a multiagent platform to different applications.

The MAS-CommonKADS approach

The definition of a software engineering methodology usually does not begin from scratch, but it is a refinement cycle, adding the new aspects and perspectives of the systems and languages and integrating the successful ingredients of previous methodologies. This is the approach followed here. Our methodology is called MAS-CommonKADS because it is an extension of the CommonKADS methodology, adding the aspects which are relevant to MAS.

CommonKADS overview

CommonKADS [de Hoog et al., 1993] is a methodology designed for the development of knowledge based systems (KBS) analogous to methods of software engineering. The development of these methods has been funded by the European Community's ESPRIT program between 1983 and 1994. A good overview of CommonKADS can be found in [Schreiber et al., 1994].

The CommonKADS methodology follows an approach to Knowledge Based System Development as the building of a number of separate models that capture salient features of the system and its environment.

The process of KBS development consists of filling a number of model templates. Associated to these model templates there are model states that characterise the landmark moments in the development of the model. These landmark states allow the management of the project, whose development proceeds in a cyclic and risk-driven way.

   figure51
Figure 1: The CommonKADS Model Set from [Schreiber et al., 1994, p.2,]

The CommonKADS model set is shown in figure 1. There are six defined models:

Limitations of CommonKADS for MAS

CommonKADS was not designed for developing MAS. The main restrictions for the direct application of CommonKADS to MAS come from the CommonKADS CM:

In the following sections, we propose an extension of CommonKADS for MAS:

MAS-CommonKADS: software development life cycle model

 

The overall MAS-CommonKADS methodology for multiagent systems development follows these phases:

Conceptualisation

The usage of use cases [Jacobson, 1992] has been introduced in most of the object oriented methodologies in the last years [Regnell et al., 1996], specially in the earliest stages of system development. The method of use case modelling presented in [Regnell et al., 1996] has the advantage of being formalized with Message Sequence Charts, which are used for modelling the proposed coordination model.

Analysis

The results of this phase will be the requirements specification of the composite system through the development of the models described before. Only the extensions to CommonKADS are developed in this paper. The steps of this phase are:

  1. Delimitation: Delimit the MAS system from the external systems. This point was carried out in CommonKADS by the development of the AM. A first version of AM and CoM are obtained. The external (predefined) systems are agentified. Both speech-acts and interchanged data are modelled in the CoM. If there is user interaction, agentify the user and develop a first version of CM.
  2. Decomposition: The system can be decomposed by the identification of more agents attending to the following guidelines [Bond & Gasser, 1988]:

  3. Validation:

Design

As a result of the analysis phase, an initial set of agents has been determined. During this phase the DM is developed, which is extended for MAS. It consists of:

Application design

The EM (mainly its task level) and the TM can help us to identify new agents. For each new agent identification, the steps of the decomposition and validation of the Analysis should be followed.

The definition of the domain knowledge of each agent is based on the domain level of the EM. The common domain knowledge for most of the agents and the coordination knowledge is extracted in the network model (section 3.3.2).

In this phase, more agents can be identified attending to the following criteria:

Architecture design

  The general architecture of the systems is, of course, a multiagent architecture. Here, the architecture design is subdivided up into the three levels of the network model of a multiagent architecture proposed in [Iglesias et al., 1996].

  1. Network level: The design decisions about the infrastructure of the multiagent architecture are taken. It is specified which agents are needed to maintain the multiagent society (facilitators, knowledge managers, group coordinators, etc.). Several answers should be answered, for example:

    The interactions needed to perform network tasks such as logging-in, logging-out, etc, can be represented in the interactions diagrams of CoM (section 5) defined as SDL tasks. In this way, this diagrams are augmented to show the design decisions.

  2. Knowledge level: Several design decisions should be taken regarding the management of ontologies:

    These public ontologies are the domain knowledge that should be common to most of the agents, and can be extracted from the domain level of the EM.

  3. Coordination level: For sake of reusability, several authors have pointed out the advantages of defining the Cooperation knowledge as a reusable module [Jennings & A., 1993] or the definition of reusable coordination protocols AgenTalk [Ishida, 1995, Kuwabara et al., 1995]. This knowledge, the set of suitable primitives [Finin & Fritzson, 1994, Huang et al., 1995] and the agents to form joint plans are the basis for the definition of this level. This knowledge should be merged (and specialised if needed) with the domain knowledge of each agent derived from the EM in the application design.

Platform design

Based on the architecture design, the agent architecture selected and the non functional requirements, the selection of the operating system and the software and hardware platform is carried out.

Coding and testing

As discussed in [Wooldridge & Fisher, 1994], this is an open-question, depending on the usage of a general purpose language or a formal agent language, which can be directly executable or translated to a executable form.

Global testing, operation and maintenance

The correct behaviour of the global system can be partially tested by using typical scenarios which deal with the possible conflicts and the methods for conflict resolution. Since the global behaviour of the system cannot be determined during analysis or design, because it depends on the particular commitments and agreements between the agents [Huang et al., 1995], simulation of the behaviours is usually needed.

Finally, the MAS is installed and maintained.

Modifications to the Agent Model

  The agent model has been modified in order to include the characteristic aspects of intelligent agents. The central constituent is the agent. It has five attributes: name, type (human, new system agent or predefined system agent), subclass-of, role, position and groups (agent groups the agent belongs to). Other constituents of this model are:

The Coordination Model

  Since the CommonKADS CM does not provide a suitable treatment of multiagent interactions, it is formulated here a different CM development based on speech-acts, which is called coordination model (CoM). This is an alternative model that can be used when the agents are software agents. The CM of CommonKADS can be used to model further human-machine communication. For the CoM, human agents are agentified and the communication is carried out via speech-acts. The design of the user interface is outside the scope of this extension.

Model structure

The Coordination model contains four costituents (figure 2):

   figure199
Figure 2: Coordination Model

Graphical notation

Three graphical models (with the corresponding textual templates) are used to develop the CoM:

CEFSMs have the special characteristic for MAS of considering three kinds of events (signals) or stimuli:

Landmark states

  There are two main landmark states during the devoloping of this model, apart from the cross-validation between models:

Model development cycle

 

The steps followed for the development of this model are:

  1. Describe the prototypical scenarios between agents. These scenarios can be a further development of the scenarios determined in the conceptualisation phase for the use cases. The scenarios are described using message sequence charts (MSCs)[Rudolph et al., 1996]. An alternative representation is event trace diagrams. During this first stage, we will consider that every conversation consists of only one single interaction and the possible answer. The objective at this stage of development is to establish the set of conversations (channels) between agents.
  2. Represent the events (interchanged messages) between agents in event flow diagrams (also called service charts). These diagrams collect the relationships between the agents via services.
  3. Model the date interchanged in each interaction. The EM can help us to define the interchanged knowledge structures. These interchanged data are shown in the event flow diagram between squared brackets.
  4. Model each interaction with CEFSMs of SDL specifying speech-acts as inputs/outputs of message events. Alternative representations are discussed in section 7. The inputs and outputs of the SDL process representation can be validated with the MSC diagrams.
  5. Each state can be further refined. If the state represent a knowledge task, the inference templates of the CommonKADS library are very useful. While decomposing a state, it can be decomposed in different agents, and the complete process should be repeated.
  6. Analyse each interaction and determine its synchronisation: synchronous, asynchronous or future.
  7. Determine the receivers of each service request: individual or group and if a coordination protocol like contract-net is desired. This can be represented in SDL using the names of the agents or group names in the explicit addressing facility.
  8. Determine if a cooperation protocol is needed for each conversation. The reasons for using a cooperation protocol can be among others [Durfee et al., 1989]:
  9. Consult the library of cooperation protocols and reuse a protocol defined previously or define its interaction model. It is very useful the utilization of HMSC (High level Message Sequence Charts) for this purpose.

From the CoM we should check the consistency with the AM:

This model allows the complete and clear specification of individual interactions. Nevertheless, the global behaviour of the system depends on the sequence of interactions carried out by the agents.

An additional advantage of using SDL is the ability for modelling coordination protocols which can be reused using tasks.

Example

 

Statement of the problem

In this section we apply the MAS-CommonKADS methodology to the development of a simplified classification system (in the following SCS). This system will be running in a power plant. The system has to predict if the value of a distinguished variable (e.g., the delivered power) is going up or down or will be constant. This classification is done from a set of values collected from sensors and filtered and stored every two minutes by an existing data acquisition system. For the shake of simplicity, we will deal with only two variables (e.g., boiler temperature and pressure).

The managers of the plant have no clear idea about the techniques that should be used for classification, as there is no analytical model available. They consider a good idea to incorporate several classification modules whose results would be presented every two minutes to a human operator in the control room of the plant.

Based on the assessment received from the system, the operator decides the control actions to be applied to the plant in order to maintain it in the desired state (desired performance, delivered power, pollution level, etc.).

Analysis

Since this is a toy-problem, we will not analyse the risk of the system development, neither the impact of the system in the organisation, but these software management issues should be considered in a real case.

First version of the AM, EM and TM

A first version of the AM is developed as recommended [Wærn & Gala, 1993, p.26,] when there are predefined systems (in our case, the collector system). Three agents are identified attending to geographical distribution criterium: Collector (for collecting data), Classifier and the User. For space limitations, we do not show the CommonKADS templates of any model. The TM of the whole system also shows these three functions.

   figure251
Figure 3: Event trace of agent conversations version 1

   figure256
Figure 4: Event flow diagram version 1

First version of CoM

The event traces of the prototypical use cases are shown in figure 3, and the corresponding event flow diagram is shown in figure 4. The interlingua shown between squared brackets in the event flow diagram has been obtained from the domain knowledge of the EM.

   figure264
Figure 5: CEFSM of service User:Interaction

Only one CEFSM is included in figure 5. This diagram is an enhancement of the first version. It includes some design issues: macro for NetworkLogIn and non-functional requirements as the Quit button of the menu.

Design

Architecture design
Since only an agent name server is needed, a centralised network agent is chosen for the system, with Yellow-Pages facilities.

   figure274
Figure 6: Event trace of agent conversations version 2

   figure279
Figure 7: Event flow diagram version 2

Application design
From the statement of the problem, two methods are considered to get the prediction: a neural and a symbolic one, which will be carried out by two agents: Ag_Neural and Ag_ID3, respectively. An additional agent (Selector) is added to select at run-time the best prediction. The event trace and event flow diagrams of this solution is shown in figure 6 and figure 7. A new version of AM and CoM are needed to add the new interactions, which are not shown here for space limitations. The Agent Description Language (ADL) [González et al., 1994] is selected to describe the agents. The ADL code is included in appendix A.

Platform design
The MIX platform [Iglesias et al., 1994, González et al., 1995] is selected because of its facilities for integration of symbolic and connectionist techniques.

Coding and testing

The services are programmed in C++ using the libraries of the MIX Platform. The diagrams of the Coordination model are a good specification of the interactions. Then the platform is tested.

Related work and Conclusions

  The main purpose of this paper is the definition of a complete software engineering methodology to MAS. This has been done by the extension of the CommonKADS methodology in two ways:

The CoM can be used in conjunction with CommonKADS (or another methodology) or in a stand alone way for describing coordination protocols for MAS systems.

SDTs [Kuwabara et al., 1995, Fisher et al., 1996, Barbuceanu & Fox, 1996], Petri nets [Ismail et al., 1996] and statecharts [Harel, 1987, Coleman et al., 1992] are different alternatives to CEFSM for dynamic modelling. The CEFSMs of SDL have been selected because they are well known, highly visual, intuitive and a good input to the implementation. The mapping between SDL and MSC concepts makes easy the utilization of both languages and the availability of tools. They seem very suitable for modelling the interactions via primitives as KQML [Finin & Fritzson, 1994], which are modelled in SDL as signals. Its nesting facility via macros makes easy the reusability of protocols and its expansion. Nevertheless, the other alternatives (specially Petri nets and statecharts) are not excluded.

In contrast with other coordination languages [Kuwabara et al., 1995, Barbuceanu & Fox, 1996] which are environments for describing and debugging coordination protocols, our CoM is not language dependent, and we have been successful in translating some of the protocols defined in [Kuwabara et al., 1995, Barbuceanu & Fox, 1996]. These results have shown that our model does not need (informal) textual explanation as the others.

In order to provide tool support, there is no current single tool that support all the proposed graphical models in this article. We are working now on an integrated environment for MAS systems that support all the SDLC, but it is in an early stage.

This methodology is been applied in two research projects in different applications. Although the examples have been relatively small, we can conclude that besides the obvious advantage of using a methodology, it should be stressed the advantages of documentation of this methodology and its facility to describe coordination protocols.

References

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ADL Code

  

#DOMAIN "example" 
#YP_SERVER "tcp://madrazo.gti.dit.upm.es:6050"
#COMM_LANGUAGE ckrl
#ONTOLOGY example.ckrl


AGENT YP_Agent -> YPAgent
END YP_Agent

AGENT Interface -> BaseAgent
  GOALS 
    Interaction: CONCURRENT interaction
  RESOURCES 
    REQ_LIBRARIES: "inter-funct.C"
    REQ_SERVICES: Start_Control
END Interface 

AGENT Selector -> BaseAgent 
	RESOURCES 
		REQ_LIBRARIES: "selec_funct.C"
		REQ_SERVICES:	give_sample; 
			suggest 
		 	CONTRACT_POLICY eval_suggestion
			REQ_MSG_STRUCT example::cost
 	SERVICES 
		start_control: CONCURRENT start_control 
END Selector 

AGENT Collector -> BaseAgent 
	RESOURCES
		REQ_LIBRARIES: "collec_funct.C"
	INTERNAL_OBJECTS
		history -> History
	GOALS 
		get_data: CONCURRENT GetData 
	SERVICES 
 		give_sample : GiveSample
		 		ANS_MSG_STRUCT example::Vector; 
 		give_history: GiveHistory 
		 		REQ_MSG_STRUCT example::Depth
		 		ANS_MSG_STRUCT example::Vector
END Collector 

// ********************* 
// Learning Agents 
// ********************* 

CLASS Classifier -> BaseAgent
	RESOURCES
 		REQ_SERVICES: Give_History
		SUBSCRIBE_TO: Learning_Group
 	GOALS 
 		daemon : CONCURRENT virtual
	SERVICES
	    suggest: CONCURRENT virtual
 		REQ_MSG_STRUCT example::Vector
	 	ANS_MSG_STRUCT example::Suggestion
END Classifier

AGENT Ag_Neural -> Classifier
	RESOURCES
		REQ_LIBRARIES: "learn_funct.C"
 	GOALS 
 		daemon : CONCURRENT LearningNeural
 	SERVICES 
 		suggest: CONCURRENT SuggestionNeural
			 	COST SNNS_cost_function 
			 	REQ_MSG_STRUCT example::StructFile
 	 		 	ANS_MSG_STRUCT example::Cost
END Ag_Neural

AGENT Ag_ID3 -> Classifier
 	RESOURCES
		REQ_LIBRARIES: "learn_funct.C"
 	GOALS 
 		daemon: CONCURRENT LearningSymbolic
 	SERVICES 
 		suggest: CONCURRENT SuggestionSymbolic
 			 REQ_MSG_STRUCT example::Vector
	 		 ANS_MSG_STRUCT example::Suggestion
			 	COST C45_cost_function 
			 	REQ_MSG_STRUCT example::StructFile
 			 	ANS_MSG_STRUCT example::Cost
END Ag_ID3

About this document ...

A Methodological Proposal for Multiagent Systems Development extending CommonKADS

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The translation was initiated by Carlos Angel Iglesias Fernandez on Miércoles, 2 de Octubre de 1996, 10:20:54 MET DST

...CommonKADS
This research is funded in part by the Commission of the European Communities under the ESPRIT Basic Research Project MIX: Modular Integration of Connectionist and Symbolic Processing in Knowledge Based Systems, ESPRIT-9119. The MIX consortium is formed by the following institutions and companies: Institute National de Recherche en Informatique et en Automatique (INRIA-Lorraine/CRIN-CNRS, France), Centre Universitaire d'Informatique (Université de Genève, Switzerland), Institute d'Informatique et de Mathématiques Appliquées de Grenoble (France), Kratzer Automatisierung (Germany), Fakultät für Informatik (Technische Universität München, Germany) and Dep. Ingeniería de Sistemas Telemáticos (Universidad Politécnica de Madrid, Spain). 
...Iglesias1#1
This research was partly
	done while the first author was visiting the Dep.\
	Ingeniería de Sistemas Telemáticos (Universidad
	Politécnica de Madrid).

...model
The 
      selection of a new name is not easy because cooperation
      model was used in KADS-I and interaction model was used by
      Kingston [Kingston, 1992] in an extension to KADS-I

...architecture
It is used agent architecture for describing a
particular agent software/hardware construction [Wooldridge & Jennings, 1995] and 
agent model for the set of requirements (skills, role, etc.) of the
CommonKADS AM

...information
Requesting or updating
     information is also modelled as a service

 


 



Carlos Angel Iglesias Fernandez 

Miércoles,  2 de Octubre de 1996, 10:20:54 MET DST