Here - Agents Lab - University of Nottingham

3.1 simpAL OverviewThe main inspiration for simpAL abstractions comes – on the one side – from theA&A model [10] and from the BDI (Belief-Desire-Intention) model, in particularfrom its implementation in existing APL, Jason in particular. On the other side,differently from existing BDI-based APL, simpAL has been conceived conceptuallyas an extension of OOP languages with a further separated abstractionlayer based on agent-oriented abstractions. The OOP layer – based on Java, butit could be any OOP language – is meant to be used solely to represent andmanipulate abstract data types and data structures in general; All the otherissues that, for instance, are related to concurrent programming (e.g. threads,synchronized methods, etc.) or I/O programming (e.g. network, GUI, OS relatedfunctionalities, etc.) are meant to be tackled using the agent-oriented abstractionlayer.By adopting a typical anthropomorphic and social view of computation,a simpAL program is given by an organization composed by a dynamic setof agents concurrently working in a shared, possibly distributed, environment.Agents are those components of the program (system) designed to perform autonomouslytasks, that can be assigned both statically and dynamically to them.Autonomously means in this case that given a task to do, they pro-actively decidewhat actions to do and when to do them, promptly reacting to relevant eventsfrom their environment, fully encapsulating the control of their behavior. To performtheir tasks, agents can create and use resources and tools, called genericallyartifacts. Artifacts are useful to represent those non-autonomous components ofour program, the basic bricks composing the environment of the organization,providing some kind of functionality or service—such as easing agent communicationand coordination (e.g. a blackboard), or interfacing agents with externalenvironment or the user (e.g. a GUI, a socket), or wrapping external systems(e.g. a data-base, a web-service) or even simply helping agent work (e.g. a sharedcounter). An artifact can be used by a single agent or can be designed to be concurrentlyand safely used by multiple agents (e.g. a shared knowledge base, ashared calendar for alarms, etc.).Agent interactions can occur in two basic ways that can be combined together:either indirectly through the environment (by using the same artifacts),or directly by means of asynchronous messages. In particular, agents have a basicset of communicative actions, that allow for sending messages either to informor ask about some data or to assign/ work with tasks. Agent-artifact interactionis based instead on the concept of use and observation, reminding the way inwhich artifacts are used by people in human environments. In order to be used,an artifact provides a set of operations, corresponding to the set of actions availableto agents to use it. This implies that the repertoire of an agent’s actionsat runtime depends on the artifacts that the agent knows and can use. Besidesoperations, the usage interface of an artifact includes also observable properties,as observable information concerning the dynamic state of the artifact whichmay be perceived and exploited by agents accordingly.136