Role Identification

 

This phase occurs early in the requirements analysis since we now concern more with an agent’s externally visible behavior rather than its structure – only approximate at this step. Because a role is also a social concept, we consider this phase to be also part of the Agent Society Model.

Roles identification is based on exploring all the possible paths of the Agents Identification diagram involving inter-agent communication. A path describes a scenario of interacting agents working to achieve a required behavior of the system. It is composed of several communication paths. A communication path is simply a “communicate” relationship between two agents in the above diagram. Each of them may belong to several scenarios, which are drawn by means of sequence diagrams in which objects are used to symbolize roles. The following figure shows the scenario discussed in the Domain Description, arising when a new purchase is required from the role Announcer of the PurchaseMonitor agent to the role BooksProvider of the Purchase Manager agent.

Each object in the diagram represents a role and we name it with the following syntax:

                    <role_name> : <agent_name>

An agent may participate in different scenarios playing distinct roles in each. It may also play distinct roles in the same scenario (e.g. the Purchaser and the PurchaseAdvisor agents in the following figure).

The Roles Identification diagram for the scenario in which the PurchaseMonitor announces the need for a books purchase

 

The messages in the sequence diagram may either signify events generated by the external environment or communication between the roles of one or more agents. A message specifies what the role is to do and possibly the data to be provided or received.

We can describe the scenario as follows:

• The Announcer informs the BooksProvider that the bookstore needs to purchase a specified stock of books.
• Given a list of suppliers for the needed books, the BooksProvider requests the PurchaseConsultant to suggest purchase conditions (number of stocks, purchase-money, etc) on the basis of past business.
• Whether the PurchaseConsultant has returned an advise or not, the BooksProvider gives the Negotiator the data about the supplier to negotiate with and the conditions to be negotiated; at the same time it requests the negotiation to be started. The BooksProvider is then ready to take care of other requests that may come from the cooperating agents’ roles.
• The Negotiator negotiates via fax or e-mail (this is the case of the present scenario) and gets the best offer. It then returns it to the BooksProvider.
• The BooksProvider establishes whether the offer is good enough or not, according to its budget and considerations such as the pricing of the book and the number of students that would then buy it. In this scenario we assume that the offer be good enough and so the BooksProvider proposes the OrderPlacer to buy the books. Therefore the BooksProvider is then ready to take care of other requests.
• When the books are delivered a notification is then forwarded from the DeliveryNotifier to the BooksProvider.

The rest of the scenario is straightforward. Data contained in the messages of the above sequence diagram are specified in more detail later in the Ontology Description phase.

 

Next phase: Task Specification

Previous phase: Agent Identification

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