Here - Agents Lab - University of Nottingham

would report an error message about missing a plan for a declared task, i.e.KeepTemperature.The second case concerns checking tasks assigned to an agent of type R,i.e. which is expected to play the role R. Task assignment can be done in twoways. The first is through a predefined communicative action do-task done byany agent specifying the typed identifier of the task recipient:do-task TaskTodo task-recipient: IdThe second is through a pre-defined internal action with the same name, withoutspecifying the target agent, so as for an agent to allocate the task to himself.In both cases, the action completes as soon as the task has been done or it hasfailed 4 . Given this, we can enforce that:– given a belief Id of type R, storing the identifier of some agent playing therole R, then for any communication action do-task t task-recipient: Id thatsends a message to the target agent to assign him the task t, there mustexist a task type T in R such that t is a value (instance) of T .Then, given a fragment of a script with e.g. a belief myThermostat declared oftype Thermostat, we have the following list of the main kind of errors that canbe caught at compile time:/* compilation ok */do-task AchieveTemperature( targetTemp: 21 ) task-recipient: myThermostat/* error: no tasks matching CleanTheRoom in role Thermostat */do-task CleanTheRoom() task-recipient: myThermostat/* error: no targetT param in AchieveTemperature */do-task AchieveTemperature( targetT: 21 ) task-recipient: myThermostat/* error: wrong type for the param value targetTemp */do-task AchieveTemperature( targetTemp: "21" ) task-recipient: myThermostatThe definition of role types includes also the type of messages that can besent to an agent playing the role, in particular what kind of beliefs can be toldby other agents. It can be declared by understands blocks. In the example,agents playing the Thermostat role can be told about the new threshold toadopt, which is represented by a belief newThreshold containing a value of typedouble (see lines 13-15 in Fig. 2). This declaration allows for checking at compiletime that the communicative actions of agents aiming at informing other agentsabout some belief. In simpAL this can be done by the communicative action:tell Bel = BelExpr to: Id4 in the case of the task assigned to another agent this is done by a message which isautomatically sent from the recipient to the task allocator.141