An Observation Approach to the Semantics of Agent Communication Languages

We show how a formal framework for the observation issue in computer systems can be used for the specification of an agent behavior, abstracting away from agent inner details while focusing on its interactive behavior. This model can also be used as a specification of agent communication languages (ACLs), providing the proper abstraction level to represent the conditions causing an agent to send a message, as well as its effect on the receiving agent. In particular, this approach generalizes upon existing ACL semantics, such as FIPA ACL, that relate agent communicative acts to the agent mental state. Since the observation framework induces a more abstract architecture than other known approaches, our semantics are likely to be applicable to a wider set of agent architectures, thus better supporting standardization aims. Some application examples are shown, describing how various aspects of ACL semantics can be specified within our framework.     

Modeling conversation policies using permissions and obligations

Both conversation specifications and policies are required to facilitate effective agent communication. Specifications provide the order in which speech acts can occur in a meaningful conversation, whereas policies restrict the specifications that can be used in a certain conversation based on the sender, receiver, messages exchanged thus far, content, and other context. We propose that positive/negative permissions and obligations be used to model conversation specifications and policies. We also propose the use of ontologies to categorize speech acts such that high level policies can be defined without going into specifics of the speech acts. This approach is independent of the syntax and semantics of the communication language and can be used for different agent communication languages. Our policy based framework can help in agent communication in three ways: (i) to filter inappropriate messages, (ii) to help an agent to decide which speech act to use next, and (iii) to prevent an agent from sending inappropriate messages. Our work differs from most existing research on communication policies because it is not tightly coupled to any domain information such as the mental states of agents or specific communicative acts. Contributions of this work include: (i) an extensible framework that is applicable to varied domain knowledge and different agent communication languages, and (ii) the declarative representation of conversation specifications and policies in terms of permitted and obligated speech acts.     

基于自我意识的agent通信语言包容性研究

针对主流agent通信语言在描述通信内容及其语义时存在一定的局限性问题,提出了基于自我意识的agent通信语言(ACLBSC)并对其包容性进行研究。首先,研究了基于自我意识的agent结构及其含义,证明基于自我意识的agent通信语言能理解其结构与含义并将其转换为通信内容;其次,分析了主流agent通信语言的语用词及其语义,研究了用基于自我意识的agent通信语言对主流agent通信语言的包容;最后通过具体通信实例对比了不同通信语言的包容性。结果表明基于自我意识的agent通信语言不仅能够很好地包容主流agent通信语言,还能模拟人类的通信模式,方便agent之间对通信内容的理解。     

Formalization of test experiments

Formal methods for testing conformance of the system under examination to its specification are examined. The operational interaction semantics is specified by a special testing machine that formally determines the testing capabilities. A set of theoretically powerful and practically important capabilities is distinguished that can be reduced to the observation of external actions and refusals (the absence of external actions). The novelties are as follows. (1) Parameterization of the semantics by the families of observable and not observable refusals, which makes it possible to take into account various constraints on the (correct) interactions. (2) Destruction as a forbidden action, which is possible but should not be performed in the case of a correct interaction. (3) Modeling of the divergence by the Δ-action, which also should be avoided in the case of a correct interaction. On the basis of this semantics, the concept of safe testing, the implementation safety hypothesis, and the safe conformance relation are proposed. The safe conformance relation corresponds to the principle of independent observations: a behavior of an implementation is correct or incorrect independently of its other possible behaviors. For a more narrow class of interactions, another version of the semantics based on the ready traces may be used along with the corresponding conformance relation. Some propositions concerning the relationships between the conformance relations under various semantics are formulated. The completion transformation that solves the problem of the conformance relation reflexivity and a monotone transformation that solves the monotonicity problem (preservation of the conformance under composition) are defined.     

Prototyping realistic programming languages based on formal specifications

The specification of realistic programming languages is difficult and expensive. One approach to make language specification more attractive is the development of techniques and systems for the generation of language–specific software from specifications. To contribute to this approach, a tool–based framework with the following features is presented: It supports new techniques to specify more language aspects in a static fashion. This improves the efficiency of generated software. It provides powerful interfaces to generated software components. This facilitates the use of these components as parts of language–specific software. It has a rather simple formal semantics. In the framework, static semantics is defined by a very general attribution technique enabling e.g. the specification of flow graphs. The dynamic semantics is defined by evolving algebra rules, a technique that has been successfully applied to realistic programming languages. After providing the formal background of the framework, an object–oriented programming language is specified to illustrate the central specification features. In particular, it is shown how parallelism can be handled. The relationship to attribute grammar extensions is discussed using a non-trivial compiler problem. Finally, the paper describes new techniques for implementing the framework and reports on experiences made so far with the implemented system. Received: 20 November 1995 / 20 January 1997     

Interaction semantics with refusals,divergence, and destruction

Formal methods for testing the conformance of a software system to its specification are considered. The interaction semantics determines the testing capabilities, which are reduced to the observation of actions and refusals (absence of actions). The semantics is parameterized by the families of observable and unobservable refusals. The concept of destruction as a prohibited action that should be avoided in the course of interaction is introduced. The concept of safe testing, the implementation safety hypothesis, safe conformance, and generation of a complete test suite based on the specification are defined. Equivalences of traces, specifications, safety relations, and interaction semantics are examined. A specification completion is proposed that can be used to remove from the specification irrelevant (not included in the safely testable implementations) and nonconformal specification traces is proposed. The concept of total testing that detects all the errors in the implementation (rather than at least one error as is the case in complete testing) is introduced. On the basis of the analysis of dependences between errors, a method for the minimization of test suites is proposed. The problem of preserving the conformance under composition (the monotonicity of conformance) is investigated, and a monotone transformation of the specification solving this problem is proposed.     

Arguments and Misunderstandings: Fuzzy Unification for Negotiating Agents

In this paper, we develop the notion of fuzzy unification and incorporate it into a novel fuzzy argumentation framework for extended logic programming. We make the following contributions: The argumentation framework is defined by a declarative bottom-up fixpoint semantics and an equivalent goal-directed top-down proofprocedure for extended logic programming. Our framework allows one to represent positive and explicitly negative knowledge, as well as uncertainty. Both concepts are used in agent communication languages such as KQML and FIPA ACL. One source of uncertainty in open systems stems from mismatches in parameter and predicate names and missing parameters. To this end, we conservatively extend classical unification and develop fuzzy unification based on normalised edit distance over trees.     

A semantic framework for metamodel-based languages

In the model-based development context, metamodel-based languages are increasingly being defined and adopted either for general purposes or for specific domains of interest. However, meta-languages such as the MOF (Meta Object Facility)—combined with the OCL (Object Constraint Language) for expressing constraints—used to specify metamodels focus on structural and static semantics but have no built-in support for specifying behavioral semantics. This paper introduces a formal semantic framework for the definition of the semantics of metamodel-based languages. Using metamodelling principles, we propose several techniques, some based on the translational approach while others based on the weaving approach, all showing how the Abstract State Machine formal method can be integrated with current metamodel engineering environments to endow language metamodels with precise and executable semantics. We exemplify the use of our semantic framework by applying the proposed techniques to the OMG metamodelling framework for the behaviour specification of the Finite State Machines provided in terms of a metamodel.