18. – 23. März 2007, Dagstuhl Seminar 07122

Normative Multi-agent Systems


Guido Boella (University of Turin, IT)
Leon van der Torre (University of Luxembourg, LU)
Harko Verhagen (Stockholm University, SE)

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Norms like obligations, permissions and prohibitions have been proposed in multi-agent systems to deal with coordination and security issues of multi-agent systems, to model legal issues in electronic institutions and electronic commerce, to model multi-agent organizations, and so on. In the context of this workshop we use the following definition: A normative multiagent system is a multiagent system together with normative systems in which agents on the one hand can decide whether to follow the explicitly represented norms, and on the other the normative systems specify how and in which extent the agents can modify the norms.

Since norms are explicitly represented, the question should be raised how norms are represented. Norms can be interpreted as a special kind of constraint, and represented depending on the domain in which they occur. Since not all agents behave according to the norm, norms are not hard constraints, but soft constraints. The question will be raised how the system monitors the behavior of agents and enforce sanctions in case of violations, or reward good behavior. Also, the question will be raised how to represent permissive norms, and how they relate to obligations. For example, the permission to access a resource under an access control system cannot be represented as a constraint. Finally, the question will be raised how norms evolve.

In electronic commerce research, for example, cognitive foundations of social norms and contracts are studied. Protocols and social mechanisms are now being developed to support such creations of norms in multiagent systems. When norms are created, the question how they are enforced will be raised. For example, when a contract is violated, the violator may have to pay a penalty. But then there has to be a monitoring and sanctioning system, for example police agents in an electronic institution. Such protocols or roles in a multiagent system are part of the construction of social reality, and such social realities are constructed by constitutive norms. This again raises the question how to represent such constitutive or counts-as norms, and how they are related to regulative norms like obligations and permissions.

Norms should therefore be represented as a domain independent theory, for example in deontic logic. Deontic logic studies logical relations among obligations, permissions, prohibitions and counts-as conditionals, and more in particular violations and contrary-to-duty obligations, permissions and their relation to obligations, and the dynamics of obligations over time. Therefore, insights from deontic logic can be used to represent and reason with norms. Deontic logic also offers representations of norms as rules or conditionals. However, there are several aspects of norms which are not covered by constraints nor by deontic logic, such as the questions where do norms come from, how are they created by a single legislator, how do they emerge spontaneously, or how are they negotiated among the agents. Moreover, what is the relation between the cognitive abilities of agents and the global properties of norms, how can agents acquire norms, how can agents violate norms, how can an agent be autonomous, how are group obligations distributed over the members of the group, and so on.

Not only the relation between norms and agents must be studied, but also the relation between norms and other social and legal concepts. How do norms structure organizations? How do norms coordinate groups and societies? How about the contract frames in which contracts live, and the legal contexts in which contract frames live? Though in some normative multiagent systems there is only a single normative system, there can also be several of them, raising the question how normative systems interact. For example, in a virtual community of resource providers each provider may have its own normative system, which raises the question how one system can authorize access in another system, or how global policies can be defined to regulate these local policies.

Summarizing, normative multiagent systems study general and domain independent properties of norms. It builds on results obtained in deontic logic for the representation of norms as rules, the application of such rules, contrary-to-duty reasoning and the relation to permissions. However, it goes beyond logical relations among obligations and permissions by explaining the relation among social norms and obligations, relating regulative norms to constitutive norms, explaining the evolution of normative systems, how agents interact with norms, and much more.

Information for the invited scientists:

During the past years we observe a rising interest in computer science and in social theory in multi-agent systems, which is moving more and more from the individual, cognitive focussed agent models to models of socially situated agents. In particular attention is given to normative multi-agent systems, because the use of norms is the key of human social intelligence. If artificial agents are to display behavior equal to human intelligent behavior or collaborate with humans, norms are essential. Norms have been mentioned in agent research for quite some time, but lately we can see that the research field has matured.

The NorMAS05 symposium at the 2005 AISB conference has raised the questions of which problems must be solved in normas, and how to approach these problems. The need for models, theories and tools in multi-agent systems has also been observed in the related area of "deontic logic of computer science", where its biannual workshops were interested in applications in multi-agent systems (DEON 2004) and artificial social systems (DEON 2006). However, the gap between the DEON community and the multi-agent systems community, due to the fact that the DEON community restricts itself to one formal language, a branch of modal logic called deontic logic, whereas in multi-agent systems also other models and languages are used, ranging from game theory to Z specifications.

Norms are also considered in various workshops in multi-agent systems concerned with for example legal issues, organizations, institutions, and so on. We have observed the need for an occasion to discuss and compare the various proposals now under development. The traditional agent workshops are not sufficient, because they are not just concerned with the norms in multi-agent systems but also with some other issues (coordination, security, etc). However, there is no common theory of normative multi-agent systems, due to the lack of a universal theory in the social sciences. Therefore, presently many multi-agent system researchers are developing their own ad hoc theories and applications.

The expected results of the seminar are to have a clear view of the ontological similarities and differences between the use of the different concepts connected to norms in the research disciplines. The goal of the seminar is to gather specialists from different areas such as computer science, logic, sociology, and cognitive science to discuss the fundamental concepts and ontologies connected to the use of norms in human and artificial systems, more in particular the use of norms as a mechanism in multi-agent systems and the use of multi-agent systems to study the concept and theories of norms and normative behavior.

Dagstuhl Seminar Series


  • Interdisciplinary


  • Normative systems
  • Multi-agent systems


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