-
The growing pervasiveness of computer networks and of Internet is an
important catalyst pushing towards the realization of business-to-business and
crossbusiness solutions. Interaction and coordination, central issues to any distributed
system, acquire in this context a special relevance since they allow the involved
groups to integrate by interacting according to the agreed contracts, to share best
practices and agreements, to cooperatively exploit resources and to facilitate the
identification and the development of new products.
The issues of interaction, coordination and communication have been
receiving great attention in the area of Multi-Agent Systems (MAS). MAS are,
therefore, the tools that could better meet these needs by offering the proper
abstractions. Particularly relevant in the outlined application context are a shared
and inspectable specification of the rules of the MAS and the verification of
global properties of the interaction, like the interoperability of the given roles,
as well as properties like the conformance of an agent specification (or of its
run-time behavior) to a protocol. In open environments, in fact, it is important
to have guaranties on how interaction will take place, coping with notions like
responsibility and commitment. Unfortunately, current proposals of platforms
and languages for the development of MAS do not supply high level tools for
directly implementing this kind of specifications. As a consequence, they do not
support the necessary forms of verification, with a negative impact on the
applicability of MAS to the realization of business-to-business and cross-business
systems.
Let us consider, for instance, JADE [
4, 18, 16, 17
], which is one of the best
known infrastructures, sticking out for its wide adoption also in business
contexts. JADE agents communicate by exchanging messages that conform to FIPA
ACL [
3
]. According to FIPA ACL mentalistic approach, the semantics of
messages is given in terms of preconditions and effects on the mental states of the
involved agents, which are assumed to share a common ontology. Agent platforms
based on FIPA exclusively provide syntactic checks of message structures,
entrusting the semantics issues to agent developers. This hinders the applicability
to open contexts, where it is necessary to coordinate autonomous and
heterogeneous agents and it is not possible to assume mutual trust among them. In these
contexts it is necessary to have an unambiguous semantics allowing the
verification of interaction properties before the interaction takes place [
52
] or during
the interaction [
9
], preserving at the same time the privacy of the implemented
policies.
The mentalistic approach does not allow to satisfy all these needs [
40
]; it is
suitable for reasoning from the local point of view of a single agent, but it does
not allow the verification of interaction properties of a MAS from a global point of
view. One of the reasons is that the reference model lacks an abstraction for the
representation, by means of a public specification, of elements like (i) resources
and services that are available in the environment/context in which agents
interact and (ii) the rules and protocols, defining the interaction of agents through the
environment/context. All these elements belong to (and contribute to make) the
environment of the interacting agents. Such an abstraction, if available, would be
the natural means for encapsulating resources, services, and functionalities (like
ontological mediators) that can support the communication and the coordination
of agents [
67, 66, 43
], thus facilitating the verification of the properties [
13
]. It
could also facilitate the interaction of agents implemented in different languages
because it would be sufficient that each language implements the primitives for
interacting with the environment [
1
]. One of the consequences of the lack of an
explicit representation of the environment is that only forms of direct
communication are possible. On the contrary, in the area of distributed systems and
also in MAS alternative communication models, such as the generative
communication based on tuple spaces [
32
], have been put forward. These forms of
communication, which do not necessarily require a space-time coupling between
agents, are not supported.
The issues that we mean to face have correspondences with issues concerning
normative MAS [
70
] and Artificial Institutions [
31, 65
]. The current proposals in
this field, however, do not supply all of the solutions that we need: either they
do not account for indirect forms of communication or they lack mechanisms for
allowing the a priori verification of global properties of the interaction. As [
31,
65
] witnes, there is, instead, an emerging need of defining a more abstract notion
of action, which is not limited to direct speech acts. In this case, institutional
actions are performed by executing instrumental actions that are conventionally
associated with them. Currently, instrumental actions are limited to speech acts
but this representation is not always natural. For instance, for voting in the
human world, people often raise their hands rather than saying the name
corresponding to their choice. If the environment were represented explicitly it would
be possible to use a wider range of instrumental actions, that can be perceived
by the other agents through the environment that acts as a medium.
Our goal is, therefore, to propose an infrastructure that overcomes such
limits. The key of the proposal is the adoption of a social approach to communication
[
45, 14, 13, 12
], based on a model that includes an explicit representation not only
of agents but also of their environment, as a collection of virtual and physical
resources, tools and services, “artifacts” as intended in the Agents & Artifacts
(A&A) meta-model [
43
], which are shared, used and adapted by the agents,
according to their goals. The introduction of environments is fundamental to
the adoption of an observational (social) semantics, like the one used in
commitment protocols, in that it supplies primitives that allow agents to perceive and to
modify the environment itself and, therefore, to interact and to coordinate with
one another in a way that satisfies the rules of the environment. On the other
hand, the observational semantics is the only sufficiently general semantics to
allow forms of interaction and of communication that do not rely solely on direct
speech acts. As a consequence we will include models where communication is
mediated by an environment, that encapsulates and applies rules and constraints
aimed at coordinating agents at the organization level, and integrates ontological
mediation functionalities. The environment will provide the contract that agents
should respect and a context into which interpreting their actions. In this way,
it will be possible to formally verify the desired properties of the interaction, a
priori and at execution time.
2
Vision
The focus of our proposal is on the definition of formal models of interactions
and of the related support infrastructures, which explicitly represent not only
the agents but also the environment in terms of rules of interaction, conventions,
resources, tools, and services that are functional to the coordination and
cooperation of the agents. These models must allow both direct and indirect forms
of communication, include ontological mediators, and enable the verification of
interaction properties of MAS from the global point of view of the system as well
as from the point of view of the single agents. The approach we plan to pursue
in order to define a formal model of interaction is based on a revision in social
terms of the interaction and of the protocols controlling it, along the lines of [
14,
13, 12
]. Furthermore, we will model the environment, in the sense introduced by
the A&A meta-model [
43
]. This will lead to the study of communication forms
mediated by the environment. The resulting models will be validated by the
implementation of software tools and of programming languages featuring the
designed abstractions. More in details, with reference to Fig. 1, the goals are:
To introduce a formal model for specifying and controlling the interaction.
The model (top level of Fig. 1) must be equipped with an observational
(commitment-based) semantics and must be able to express not only
direct communicative acts but also interactions mediated by the environment.
This will enable forms of verification that encompass both global interaction
properties and specific agent properties such as interoperability and
conformance [
11
]. The approach does not hinder agent autonomy, it guarantees the
privacy of the policies implemented by the agents, and consequently favors
the composition of heterogeneous agents. The model will be inspired by the
social approach introduced in [
45
] and subsequently extended in [
14, 13, 12
].
To define high-level environment models supporting the forms of
interactions and coordination between agents outlined above. These models must
support: interaction protocols based on commitments; the definition of rules
on the interaction; forms of mediated communication and coordination
between agents (such as stigmergic coordination). They must also enable forms
of a priori and runtime verification of the interaction. To these aims, we plan
to use the A&A meta-model [
58, 67, 43, 56
] and the corresponding notion of
programmable environment [
57
] (programming abstractions level of Fig. 1).
To integrate ontologies and ontological mediators in the definition of the
models so as to guarantee openness and heterogeneity of MAS. Mediation
will occur at two distinct levels: the one related to the vocabulary and
domain of discourse and the one that characterizes the social approach where
it is required to bind the semantics of the agent actions with their meaning
in social terms. Ontological mediators will be realized as artifacts.
To integrate the abstractions defined in the above models within
programming languages and frameworks. In particular, we plan to integrate the
notions of agents, of environment, of direct and mediated communication, and
of ontological mediators. Possible starting points are the aforementioned
FIPA ACL standard and the works that focus on the integration of
agentoriented programming languages with environments [
55
]. The JaCa platform
[
57
], integrating Jason and CArtAgO, will be taken as reference. This will
form the execution platform of Fig. 1 and will supply the primitives for
interacting with the environments.
To develop an open-source prototype of software infrastructure for the
experimentation of the defined models. The prototype will integrate and
extend existing technologies such as JADE [
18, 16, 17
] (as a FIPA-compliant
framework), CArtAgO [
1
] (for the programming and the execution of
environments), Jason (as a programming language for BDI agents), MOISE [
35
]
(as organizational infrastructure).
To identify applicative scenarios for the evaluation of the developed
models and prototypes. In this respect we regard the domain of Web services
as particularly relevant because of the need to deploy complex interactions
having those characteristics of flexibility that agents are able to guarantee.
Another interesting application regards the verification of adherence of
bureaucratic procedures of public administration with respect to the current
normative. Specific case studies will be defined in collaboration with those
companies that have stated interest towards the project.
3
State of Art
These novel elements, related to the formation of and the interaction within
decentralized structures, find an initial support in proposals from the literature in
the area of MAS. Current proposals, however, are still incomplete in that they
supply solutions to single aspects. For instance, electronic institutions [
28, 10, 35,
34
] regulate interaction, tackle open environments and their semantics allows the
verification of properties but they only tackle direct communication protocols,
based on speech acts, and do not include an explicit notion of environment.
Commitment protocols [
45, 69
], effective in open systems and allowing more general
forms of communication, do not supply behavioral patterns, and for this reason
it is impossible to verify properties of the interaction. Eventually, most of the
models and architectures for environments prefigure simple/reactive agent
models without defining semantics, that are comparable to the ones for ACL, and
without explaining how such proposals could be integrated with direct
communication models based on speech acts. We classify the relevant contributions in
the literature according to the objectives and the methodological aspects that
will be examined in-depth along the project.
3.1
Formal Models for Regulating the Interaction in MAS
This topic has principally been tackled by modeling interaction protocols. Most
of protocol representations refer to classic models, such as Petri nets, finite state
machines, process algebras, and aim at capturing the expected interaction flow.
An advantage of this approach is that it supports the verification of interaction
properties [
52, 21, 11
], such as: verifying the interoperability of the system and
verifying if certain modifications of a system preserve some desired properties (a
crucial issue in open domains where agents can enter/leave the system at any
time). Singh and colleagues criticize the use of procedural specifications because
too rigid [
60, 24, 69
]: agents cannot take advantage of opportunities that emerge
along the interaction and that are not foreseen by their procedure. Another
issue is that communication languages use a BDI semantics (FIPA ACL is an
example), where each agent has goals and beliefs of its own. At the system
level, however, it is impossible to perform introspection of agents, which are, for
this reason, black boxes. For what concerns the verification of properties this
approach allows agents to draw conclusions about their own behavior but not to
verify global properties of the system [
40, 64
].
Both problems are solved by commitment protocols [
45, 60
], which rely on an
observational semantics of the interaction and offer adequate flexibility to agents.
Moreover, they do not require the spatio-temporal coupling of agents (as instead
direct communication does). Another advantage is that, though remaining black
boxes, agents agree on the meaning of the social actions of the protocol. Since
interactions are observable and their semantics is shared, each agent should
be able to draw conclusions concerning the system as a whole. Unfortunately,
besides some preliminary studies [
61
], the state of art does not contain proposals
on how performing the verifications in a MAS, ruled by this kind of protocols. A
relevant feature seems to be the introduction, within commitment protocols, of
behavioral rules which constrain the possible evolutions of the social state [
13,
12
].
3.2
Environment Models
The notion of environment has always played a key role in the context of MAS;
recently, it started to be considered as a first-class abstraction useful for the
design and the engineering of MAS [
67
]. A&A [
43
] follows this perspective, being
a meta-model rooted upon Activity Theory and Computer Support Cooperative
Work that defines the main abstractions for modeling a MAS, and in particular
for modeling the environment in which a MAS is situated. A&A promotes a
vision of an endogenous environment, that is a sort of software/computational
environment, part of the MAS, that encapsulates the set of tools and resources
useful/required by agents during the execution of their activities. A&A
introduces the notion of artifact as the fundamental abstraction used for modeling the
resources and the tools that populates the MAS environment. The introduction
of the environment as a new first-class abstraction requires new engineering
approaches for programming the MAS environment. The CArtAgO framework [
57
]
has been devised precisely for copying this new necessity. It provides the basis for
the engineering of MAS environments on the base of: (i) a proper computational
model and (ii) a programming model for the design and the development of the
environments on the base of the A&A meta-model. In particular, it provides
those features that are important from a software engineering point of view:
abstraction, it preserves the agent abstraction level, since the main concepts used
to define application environments, i.e. artifacts and workspaces, are first-class
entities in the agents world, and the interaction with agents is built around the
agent-based concepts of action and perception (use and observation); modularity
and encapsulation, it provides an explicit way to modularize the environment,
where artifacts are components representing units of functionality,
encapsulating a partially-observable state and operations; extensibility and adaptation, it
provides a direct support for environment extensibility and adaptation, since
artifacts can be dynamically constructed (instantiated), disposed, replaced, and
adapted by agents; reusability, it promotes the definition of types of artifact
that can be reused as tools in different application contexts, such as in the case
of coordination artifacts empowering agent interaction and coordination, such
as blackboards and synchronizers. These features will be advantageous in the
realization of the second goal of the project, w.r.t. approaches like [
25
], where
commitment stores, communication constraints and the interaction mechanisms
reside in the middleware, which shields them from the agents. This has two
disadvantages: the first is that even though all these elements are accounted for in
the high level specification, the lack of a corresponding programming abstraction
makes it difficult to verify whether the system corresponds to the specification;
the second is a lack of flexibility, in that it is not possible for the agents to
dynamically change the rules of interaction or to adopt kinds of communication
that are not already implemented in the middleware.
In the state of the art numerous applications of the endogenous environments,
i.e. environments used as a computational support for the agents’ activities, have
been explored, including coordination artifacts [
44
], artifacts used for realizing
argumentation by means of proper coordination mechanisms [
42
], artifacts used
for realizing stigmergic coordination mechanisms [
54, 48
], organizational artifacts
[
34, 49, 50
]. Even if CArtAgO can be considered a framework sufficiently mature
for the concrete developing of software/computational MAS environments it can
not be considered “complete” yet. Indeed at this moment the state of the art and
in particular the CArtAgO framework are still lacking: (i) a reference standard
on the environment side comparable to the existing standards in the context of
the agents direct communications (FIPA ACL), (ii) the definition of a rigorous
and formal semantics, in particular related to the artifact abstraction, (iii) an
integration with the current communication approaches (FIPA ACL, KQML,
etc.), and finally (iv) the support of semantic models and ontologies.
3.3
Multi-agent Organizations and Institutions
The possibility of controlling and specifying interactions is relevant also for areas
like the organizational theory [
39, 70, 15, 35
] and electronic institutions [
28, 10
]
areas. Tendentiously, the focus is orthogonal to the one posed on interaction
protocols, in that it concerns the modeling of the structure rather than of the
interaction.
The abstract architecture of e-Institutions (e.g. Ameli [
28
]), places a
middleware composed of governors and staff agents between participating agents and
an agent communication infrastructure (e.g. JADE [
18, 16, 17
]). The notion of
environment is dialogical: it is not something agents can sense and act upon but
a conceptual one that agents, playing within the institution, can interact with by
means of norms and laws, based on specific ontologies, social structures, and
language conventions. Agents communicate with each other by means of speech acts
and, behind the scene, the middleware mediates such communication. The
extension proposed for situated e-Institutions [
10
] introduces the notion of “World
of Interest” to model the environment, that is external to the MAS but which is
relevant to the MAS application. The infrastructure of the e-Institution, in this
case, mediates also the interaction of the agents in the MAS with the view of
the environment that it supplies. Further along this line, but in the context of
organizations, ORA4MAS [
34
] proposes the use of artifacts to enable the access
of the agents in the MAS to the organization, providing a working environment
that agents can perceive, act upon and adapt. Following the A&A perspective,
they are concrete bricks used to structure the agents’ world: part of this world is
represented by the organizational infrastructure, part by artifacts introduced by
specific MAS applications, including entities/services belonging to the external
environment.
According to [
10
] there are, however, two significant differences among
artifacts and e-Institutions: (i) e-Institutions are tailored to a particular, though
large, family of applications while artifacts are more generic; (ii) e-Institutions
are a well established and proven technology that includes a formal foundation,
and advanced engineering and tool support, while for artifacts, these features are
still in a preliminary phase. One of the aims of MERCURIO is to give to artifacts
both the formal foundation (in terms of commitments and interaction patterns)
and the engineering tools that they are still missing. The introduction of
interaction patterns with an observational nature, allowing the verification of global
properties, that we aim at studying, will allow the realization of e-Institutions
by means of artifacts. The artifact will contain all the features necessary for
monitoring the on-going interactions and for detecting violations. A second step
will be to consider organizations and realize them again by means of artifacts.
To this aim, it is possible to exploit open source systems like CArtAgO [
1
],
for the programming and the execution of environments, and MOISE [
35
], as
organizational infrastructure.
3.4
Semantic Mediation in MAS
The problem of semantic mediation at the vocabulary and domain of discourse
levels was faced for the first time by the “Ontology Service Specification” [
8
]
issued by FIPA in 2001. According to that specification, an “Ontology Agent”
(OA, for short) should be integrated in the MAS in order to provide services such
as translating expressions between different ontologies and/or different content
languages and answering queries about relationships between terms or between
ontologies. Although the FIPA Ontology Service Specification represents the first
and only attempt to analyze in a systematic way the services that an OA should
provide for ensuring semantic interoperability in an open MAS, it has many
limitations. The main one is the assumption that each ontology integrated in
the MAS adheres to the OKBC model [
6
]. Currently, in fact, the most widely
accepted ontology language is OWL [
7
] which is quite different from OKBC and
cannot be converted to it in an easy and automatic way. Also, agents are allowed
to specify only one ontology as reference vocabulary for a given message, which
is a strong limitation since an agent might use terms from different ontologies in
the same message, and hence it might want to refer to more than one ontology
at the same time.
Maybe due to these limitations, there have been really few attempts to
design and implement OAs. The first dates back to 2001 [
62
] and realizes an OA
for the COMTEC platform that implements a subset of the services of a generic
FIPA-compliant OA. In 2007 [
46
] integrated an OA into AgentService, a FIPA
compliant framework based on .NET [
63
]. Ontologies in AgentService are
represented in OKBC, and hence the implementation of their OA is fully compliant
with the FIPA specification, although the offered services are a subset of the
possible ones. The only two attempts of integrating a FIPA-compliant OA into
JADE, we are aware of, are [
41
], and [
23
]. Both follow the FIPA specification
but adapt it to ontologies represented in OWL. The first proposal is aimed at
storing and modifying OWL ontologies: the OA agent exploits the Jena library
[
36
] to this aim. The second proposal, instead, faces the problem of “answering
queries about relationships between terms or between ontologies”. The solution
proposed by the authors exploits ontology matching techniques [
29
]. Apart from
[
23
], no other existing proposal faces that problem. Among non FIPA-compliant
solutions, we mention [
37
], which focuses on the process of mapping and
integrating ontologies in a MAS thanks to a set of agents which collaborate together,
and the proposal in [
47
], which implements the OA as a web service, in order to
offer its services also over the Internet.
As far as semantic mediation at the social approach level is concerned, we are
aware of no proposals in the literature. In order to take the context of count-as
rules into account, we plan to face this research issue by exploiting context aware
semantic matching techniques, that extend and improve those described in [
38
].
3.5
Software Infrastructures for Agents
The tools currently available to agent developers fail in supporting both
semantic interoperability and goal-directed reasoning. Nowadays, the development of
agents and multi-agent systems is based on two kinds of tools: agent platforms
and BDI (or variations) development environments. Agent platforms, such as
JADE [
18, 16, 17
] and FIPA-OS [
2
] provide only a transport layer and some
basic services, but they do not provide any support for goal-directed behavior.
Moreover, they lack support for semantic interoperability because they do not
take into account the semantics of the ACL they adopt. The available BDI
development environments, such as Jadex [
22
] and 2APL [
27
], support only syntactic
interoperability because they do not exploit their reasoning engines to integrate
the semantics of the adopted ACL.
The research on Agent Communication Languages (ACL) is constantly
headed towards semantic interoperability [
33
] because the most common ACLs, e.g.,
KQML [
30
] and FIPA ACL [
3
], provide each message with a declarative semantics
that was explicitly designed to support goal-directed reasoning. Unfortunately,
the research on ACLs only marginally investigated the decoupling properties of
this kind of languages (see, e.g., [
19, 20
]). To support the practical development
of software agents, several programming languages have thus been introduced
to incorporate some of the concepts from agent logics. Some languages use
actions as their starting point to define commitments (Agent-0, [
59
]), intentions
(AgentSpeak(L), [
53
]) and goals (3APL, [
26
]).
4
Expected Results
The achievements expected from this research are of different natures: scientific
result that will advance the state of the art, software products deriving from the
development of implementations, and upshots in applicative settings.
The formal model developed in MERCURIO will extend commitment
protocols by introducing behavioral rules. The starting point will be the work done
in [
14, 13, 12
]. This will advance the current state of the art with respect to the
specification of commitment protocols and also with respect to the verification
of interaction properties (like interoperability and conformance), for which there
currently exist only preliminary proposals [
61
]. Another advancement concerns
the declarative specification of protocols and their usage by designers and
software engineers. The proposals coming from MERCURIO conjugate the flexibility
and openness features that are typical of MAS with the needs of modularity and
compositionality that are typical of design and development methodologies. The
adoption of commitment protocols makes it easier and more natural to represent
(inter)actions that are not limited to communicative acts but that include
interactions mediated by the environment, namely actions upon the environment
and the detection of variations of the environment ruled by “contracts”.
For what concerns the coordination infrastructure, a first result will be the
definition of environments based on the A&A meta-model and on the CArtAgO
computational framework, that implement the formal models and the
interaction protocols mentioned above. A large number of the environments, described
in the literature supporting communication and coordination, have been stated
considering purely reactive architectures. In MERCURIO we will formulate
environment models that allow goal/task-oriented agents (those that integrate
proactivities and re-activities) the participation to MAS. Among the specific results
related to this, we foresee an advancement of the state of the art with respect
to the definition and the exploitation of forms of stigmergic coordination [
54
] in
the context of intelligent agent systems. A further contribution regards the
flexible use of artifact-based environments by intelligent agents, and consequently
the reasoning techniques that such agents may adopt to take advantage of these
environments. First steps in this direction, with respect to agents with BDI
architectures, have been described in [
51, 48
].
The MERCURIO project aims at putting forward an extension proposal for
the FIPA ACL standard, where the FIPA ACL-based communication is
integrated with forms of interactions, that are enabled and mediated by the
environment. This will lead to an explicit representation of environments as first-class
entities (in particular endogenous environments based on artifacts) and of the
related model of actions/perceptions. Furthermore we will formulate an improved
version of the MAS programming language/framework JaCa, where we plan to
integrate the agent-oriented programming language Jason, which is based on a
BDI architecture, with the CArtAgO computational framework. This result will
extend the work done so far in this direction [
55, 57
].
In MERCURIO we will implement a prototype of the reference
infrastructural model defined by the project. The prototype will be based on the
development and integration of existing open-source technologies including JADE [
4
],
the reference FIPA platform, CArtAgO [
1
], the reference platform and
technology for the programming and execution of environments, and agent-oriented
programming languages such as Jason [
5
] and 2APL [
27
]. The software platform
will include implementations of the “context sensitive” ontology alignment
algorithms developed in MERCURIO. The algorithms will be evaluated against
standard benchmarks and also against the case studies devised in MERCURIO.
Aside from the effects on research contexts, we think that the project may
give significant contributions also to industrial applicative contexts, in particular
to those companies working on software development in large, distributed
systems and in service-oriented architectures. Among the most interesting examples
are the integration and the cooperation of e-Government applications (services)
spread over the nation. For this reason, MERCURIO will involve some
companies in the project, and in particular in the definition of realistic case studies
against which the project’s products will be validated. As regards (Web) services,
some fundamental aspects promoted by the SOA model, such as autonomy and
decoupling, are addressed in a natural way by the agent-oriented paradigm.
Development and analysis of service-oriented systems can benefit from the increased
level of abstraction offered by agents, by reducing the gap between the modeling,
design, development, and implementation phases.
Acknowledgements
We thank S. Mantix for the valuable support and helpful discussions.