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Pesticides occur frequently in surface water. We used a combination of monitoring and modelling to assess the fate of pesticides at the catchmentscale. We continuously (sampling interval of eight hours) monitored eight pesticides (atrazine, carbendazim, chloridazon, diuron, isoproturon, lenacil and simazine) in surface water of two Belgian catchments. The surface water showed hourly variations in pesticide concentrations, temporarily exceeding ecotoxicological thresholds. We used the SWAT model to predict hydrology and pesticide fluxes from agricultural land to the river at the catchment scale. In addition, we used an extended version of the RWQM1 model to calculate inriver transformation of pesticides. The models adequately reconstructed the highly dynamic behaviour of the pesticides in the river. The simulations further demonstrated the importance of point sources due to poor agricultural practices and the effectiveness of measures to reduce pesticide inputs into surface water. [ABSTRACT FROM AUTHOR]

There is little or no guidance to systematically design a self-organising emergent solution that achieves the desired macroscopic behaviour. This paper describes decentralised coordination mechanisms such as gradient fields as design patterns, similar to patterns used in mainstream software engineering. As a consequence, a structured consolidation of best practice in using each coordination mechanism becomes available to guide engineers in applying them, and to directly decide which mechanisms are promising to solve a certain problem. As such, self-organising emergent solutions can be engineered more systematically, which is illustrated in a packet delivery service application. [ABSTRACT FROM AUTHOR]

This paperThe described work is part of the EUREKA-ITEA AGILE project, and partly funded by the Flemish government institution IWT (Institute for the Promotion of Innovation by Science and Technology in Flanders). takes a look at how XP and other agile practices can improve a software process for the development of avionics software. Developers of mission critical airborne software are heavily constrained by the RTCA DO-178B regulations [8]. These regulations impose strict rules regarding traceability and documentation that make it extremely hard to employ an iterative software development process. In particular, the extra validation overhead increases the time spent on small iteration cycles (for example, a bug-fix) to several weeks. Currently, this sector is also pressed to switch to a more agile, customer driven approach. In this paper we investigate how to speed up development and cope with changing requirements using agile techniques. The research was carried out in cooperation with Barco, a major Belgian avionics equipment supplier. We explain why certain agile techniques have less effect as the project progresses. We point out the stadia in which each XP practice is beneficial and where XP practices might cause a slowdown. [ABSTRACT FROM AUTHOR]

Automatic Guided Vehicles (AGVs) are unmanned vehicles that can transport loads in a warehouse. AGVs are instructed by on-board AGV control software. As multiple AGVs operate in a decentralized manner in the warehouse environment, conflicts may arise. Consequently, it is crucial to test thoroughly whether the AGV control software actually handles the potential conflicts in the appropriate way. In this paper, we employ a simulated warehouse environment to test the AGV control software. The AGV control software is embedded and activated in the simulated warehouse environment. The simulated warehouse environment provides support for testing by means of (1) representing dynamism in the warehouse environment in an explicit manner, and (2) detecting conflicts of dynamism in an automated way. The approach is illustrated for the case of testing collision avoidance. [ABSTRACT FROM AUTHOR]

In situated multi-agent systems (situated MASs), agents are explicitly placed in an environment. A situated agent does not not use long-term planning to decide what action sequence should be executed, but selects actions on the basis of its current position, the world it perceives and limited internal state. Situated agents exploit the environment to coordinate their behavior and to reach a common goal. In a recent project, we applied situated MASs to the control of an automated transportation system that uses automatic guided vehicles (AGVs) to transport loads in a warehouse. In contrast to traditional approaches where the AGVs are controlled by a central server, in this project we model the AGVs as agents in a situated MAS, aiming to improve flexibility and openness. Since the physical environment of AGVs is very restricted, it offers little opportunities for agents to use the environment. We introduce a virtual environment for agents to live in. This virtual environment (1) offers a medium that agents can use to exchange information and coordinate their behavior, and (2) serves as a suitable abstraction to shield low-level physical processing from the AGV agents. Since the only infrastructure available to the AGVs is a wireless network, the virtual environment is necessarily distributed over the AGVs. Synchronization of the state of the virtual environment is provided by ObjectPlaces, a middleware infrastructure that offers support to exchange and share information among nodes in mobile and ad-hoc networks. In this paper, we demonstrate how the environment is used creatively in the design of a MAS solution, helping to manage the complexity of engineering a complex real-world application. [ABSTRACT FROM AUTHOR]

This paper analyses the concept of an environment for multi-agent systems from the perspective of a class of manufacturing control systems using stigmergy. The discussion reveals that significant responsibilities can be attributed to the environment as an essential abstraction in MAS. Analysis shows that the environment is well positioned to manage functionalities of multi-agent systems that otherwise would be scattered over the agents, execution platform and communication infrastructure. Importantly, the environment represents a significant contribution handling the complexity of manufacturing control applications and providing a common repository for subsystems originating from different parties. [ABSTRACT FROM AUTHOR]

There is a lot of confusion on what the environment of a multi-agent system (MAS) comprises. Sometimes, researchers refer to the environment as the logical entity of a MAS in which the agents and other resources are embedded. Sometimes, the notion of environment is used to refer to the software infrastructure on which the MAS is executed. Sometimes, environment even refers to the underlying hardware infrastructure on which the MAS runs. Our research focuses on situated MASs, i.e. MASs in which agents have an explicit position in the environment. In this paper, we propose a three-layer model for situated MASs that considers agents as well as the environment as first-order abstractions. The aim of this model is to clarify the confusion between the concept of the environment and the infrastructure on which the MAS is deployed. The top layer of the model consists of the MAS application logic, the middle layer contains the software execution platform, and the physical infrastructure is located in the bottom layer. Starting from this model, we propose a classification of situated MASs based on the physical infrastructure of the MAS. We illustrate the different classes with examples from the research community and our own practice. We apply the three-layer model to each example. The models show that agents and the environment are abstractions that crosscut the three layers of the model. [ABSTRACT FROM AUTHOR]

The goal of engineering self-organising emergent systems is to acquire a macroscopic system behaviour solely from autonomous local activity and interaction. Due to the non-deterministic nature of such systems, it is hard to guarantee that the required macroscopic behaviour is achieved and maintained. Before even considering a self-organising emergent system in an industrial context, e.g. for Automated Guided Vehicle (AGV) transportation systems, such guarantees are needed. An empirical analysis approach is proposed that combines realistic agent-based simulations with existing scientific numerical algorithms for analysing the macroscopic behaviour. The numerical algorithm itself obtains the analysis results on the fly by steering and accelerating the simulation process according to the algorithm's goal. The approach is feasible, compared to formal proofs, and leads to more reliable and valuable results, compared to mere observation of simulation results. Also, the approach allows to systematically analyse the macroscopic behaviour to acquire macroscopic guarantees and feedback that can be used by an engineering process to iteratively shape a self-organising emergent solution. [ABSTRACT FROM AUTHOR]

Self-adaptation is currently addressed in general frameworks and reference architectures but not in the application architecture. This paper defines concrete concepts to specify timing driven self-adaptation in the software architecture. This self-adaptation is aimed at high-end embedded component based applications. We create an architectural view of a music application describing this kind of adaptation and discuss its implementation. The novelty of our approach is the definition of separate constructs for the monitoring, the adaptation decision logic and the adaptation itself. This allows independent specification of policy and mechanisms and the possibility to adapt other applications in order to satisfy important constraints. The implementation itself consists of reusable run-time counterparts of the constructs. These counterparts are managed by the component middleware and configured by the architectural specification. This way one does not need to write additional self-adaptation code. [ABSTRACT FROM AUTHOR]

In order to construct and deploy large-scale multi-agent systems, we must address one of the fundamental issues of distributed systems, the possibility of partial failures. This means that fault-tolerance is an inevitable issue for large-scale multi-agent systems. In this paper, we discuss the issues and propose an approach for supporting fault-tolerance of multi-agent systems. The starting idea is the application of replication strategies to agents, the most critical agents being replicated to prevent failures. As criticality of agents may evolve during the course of computation and problem solving, and as resources are bounded, we need to dynamically and automatically adapt the number of replicas of agents, in order to maximize their reliability and availability. We will describe our approach and related mechanisms for evaluating the criticality of a given agent (based on application-level semantic information, e.g. interdependences, and also system-level statistical information, e.g., communication load) and for deciding what strategy to apply (e.g., active or passive replication) and how to parameterize it (e.g., number of replicas). We also will report on experiments conducted with our prototype architecture (named DimaX). [ABSTRACT FROM AUTHOR]

Issues related to large scale systems made of autonomous components encompass interoperability among independently developed software and adaptability to changing environmental conditions. Formal specifications are traditionally used at design time for software engineering tasks. However, recently, several attempts of using formal specifications at run-time have been realised that let envisage a future use of formal specifications at run-time that will enhance interoperability and adaptability of autonomous components. This paper intends to highlight the potentialities of the use of formal specifications at run-time as a support for the correct execution of such components. This paper reviews and discusses the use of formal specifications at run-time from different perspectives: software engineering, run-time code evolution, adaptive middleware, trust and security, or business applications. It highlights the potentialities of the use of formal specifications at run-time as a support for interoperability and adaptability of interacting autonomous components. It identifies as well application domains and open issues related to the combination of specifications and code in the framework of large scale systems. [ABSTRACT FROM AUTHOR]

Tropos is an agent-oriented development methodology based on knowledge-level concepts (such as actor, goal, and the dependency between actors) with a particular focus on requirements analysis. This paper presents a pattern language for guiding developers, especially those without previous Tropos experience, through the various design challenges faced when using Tropos. The patterns format allows us to motivate the modelling constructs, justify each of the development stages, and address specific modelling problems. These patterns are inter-linked in such a way that developers can navigate from higher-level to lower-level patterns as they apply the Tropos methodology. The paper has two goals: to motivate the use of agent-oriented methodologies such as Tropos to a wider set of developers, and to provide guidance for the different development activities of the Tropos methodology. Specifically, we focus on the development stages, models, and diagrams of Tropos. The patterns in this paper cover the early and late requirements analysis stages. [ABSTRACT FROM AUTHOR]

A crucial part of multi-agent system design is the design of agent interactions. Traditional approaches to designing agent interaction use interaction protocols, which focus on defining legal sequences of messages. Such approaches do not naturally exhibit flexibility and robustness, and are not a good match for intelligent software agents which are autonomous, proactive, flexible and robust. The Hermes approach to designing agent interaction uses interaction goals, actions, and a number of failure recovery mechanisms to give a design methodology which is a good fit with intelligent software agents. However, the Hermes approach only covers part of the design process. In this paper we integrate Hermes with the Prometheus methodology, thus providing a complete methodology for designing multi-agent systems where interaction design is goal-oriented, yielding flexible and robust interactions. [ABSTRACT FROM AUTHOR]

We argue that it is useful to study classes of Multi-Agent System (mas) architectures, corresponding to architectural styles in addition to particular architectures. In this work we focus on a particular abstraction level where mas architectural styles are characterized according to properties, such as, the type of control used (from fully centralized to fully distributed), and the type of coordination used. Different architectural styles support different quality attributes to different extent. When choosing architectural style for a given application domain, we argue that it is important to evaluate the them according to the quality attributes relevant to that application. The architectural style that provides the most appropriate balance between these attributes should then be selected. As a case study we investigate the problem of dynamic and distributed resource allocation and compare six mas architectural styles that can be used to handle this task. We also illustrate the use of the Analytic Hierarchy Process, which is a basic approach to select the most suitable alternative from a number of alternatives evaluated with respect to several criteria, for selecting the architectural style that balance the trade-off between the relevant quality attributes in the best way. [ABSTRACT FROM AUTHOR]

Software reuse technologies have been a driving force in significantly reducing both the time and cost of software specification, development, maintenance and evolution. However, the dynamic nature of highly autonomous agents in distributed systems is difficult to specify with existing requirements analysis and specification techniques. This paper offers an approach for open, agent-based distributed software systems to capture requirements specifications in such a way that they can be easily reused during the initial requirements phase as well as later if the software needs to be updated. The contribution of this paper is to provide a reusable requirements specification pattern to capture the dynamically changing design configurations of agents and reuse them for future similar systems. This is achieved by adopting a product-line approach for agent-based software engineering. We motivate and illustrate this work through a specific application, a phased deployment of an agent-based, distributed microsatellite constellation. [ABSTRACT FROM AUTHOR]

Despite the relevance of the concept of role for conceptual modeling and agent-orientation, there is still in the literature a lack of consensus on the meaning of this notion and how it should be incorporated in existing conceptual modeling languages and frameworks. In this paper, we offer a contribution to this problem by employing a well-founded reference ontology (UFO) to analyze and reconcile two competing notions of role existing in the conceptual modeling literature. Moreover, a modeling solution based on this ontology is proposed, which incorporates the benefit of the two approaches analyzed. [ABSTRACT FROM AUTHOR]

MAS development requires an appropriate methodology. Rather than seek a single, ideal methodology, we investigate the applicability of method engineering, which focuses on project-specific methodology construction from existing method fragments and provides an appealing approach to organize, appropriately access and effectively harness the software engineering knowledge of MAS methodologies. In this context, we introduce a generic metamodel to serve as a representational infrastructure to unify the work product component of MAS methodologies. The resultant metamodel does not focus on any class of MAS, nor does it impose any restrictions on the format of the system requirements; rather, it is an abstraction of how the work product elements in any MAS are structured and behave both at design time and run-time. Furthermore, in this paper we validate this representational infrastructure by analysing two well-known existing MAS metamodels. We sketch how they can be seen as subtypes of our generic metamodel, providing early evidence to support the use of our metamodel towards the construction of situated MAS methodologies. [ABSTRACT FROM AUTHOR]

In this paper, we examine the Multiagent Systems Engineering (MaSE) methodology and its applicability to developing organization-based multiagent systems, which are especially relevant to context aware systems. We discuss the inherent shortcomings of MaSE and then present our approach to modeling the concepts required for organizations including goals, roles, agents, capabilities, and the assignment of agents to roles. Finally, we extend MaSE to allow it to overcome its inherent shortcomings and capture the organizational concepts defined in our organization metamodel. [ABSTRACT FROM AUTHOR]

The multi-agent paradigm promises to provide systems with the ability to adapt to changing external contexts. In this paper, we propose an approach for the model-driven design of context-aware multi-agent systems. We provide a classification for differentiating between different aspects of context and present a specification technique for modeling these aspects. We finally discuss the difficult transition from general requirements to implemented solution and propose some techniques. [ABSTRACT FROM AUTHOR]

According to social / psychological theories like Activity Theory (AT), artifacts plays a fundamental role in the context of human organisations for supporting cooperative work and, more generally, complex collaboration activities. Artifacts are either physical or cognitive tools that are shared and exploited by the collectivity of individuals for achieving individual as well as global objectives. The conceptual framework of artifacts for MAS is meant to bring the same sort of approach to multiagent systems (MAS). In particular, coordination artifacts are the entities used to shape the agent environment so as to fruitfully enable, promote and govern cooperative and social activities of agent ensembles. Thus, coordination artifacts also capture and extend the notion of coordination medium as coming from the distributed system and DAI fields, by generalising over abstractions like blackboards, tuple spaces and channels. In this paper we account for the current state of the research on coordination artifacts. First we discuss the background from AT to artifact for MAS, then we summarise the model for the coordination artifact abstraction, and the state-of-the-art of the research on models, methods and technologies currently available for engineering MAS application with coordination artifacts. [ABSTRACT FROM AUTHOR]

Large-scale multiagent systems will be the key software technology driving several future application scenarios. We envision a future in which clouds of microcomputers can be sprayed in an environment to provide, by spontaneously networking with each other, an endlessly range of futuristic applications. Beside this vision, similar kind of large-scale "spray" multiagent systems will be employed in several other scenarios ranging from ad-hoc networks of embedded and mobile devices to worldwide distributed computing. All of these scenarios present strong commonalities from the application development point of view, and new approaches and methodologies will be likely to apply, to some extent, to all of them. In particular, we argue that the issues related to the design and development of such spray multiagent systems call for novel approaches exploiting self-organization as first-class tools. With this regard, we survey a number of research projects around the world trying to apply self-organization to large-scale multiagent systems. Finally, we attempt at defining a rough research agenda that - in the long run - should integrate these ideas to develop a general and more assessed methodology for large-scale spray multiagent systems crosscutting several application domains. [ABSTRACT FROM AUTHOR]

A multiagent application consists of an environment and a number of agents. The environment contains information that the agents use and manipulate to do their work. When a multiagent system is decentralized over a number of different hosts (i.e. more than one execution platform is used), the environment has to be decentralized as well. The distributed layout of the environment can influence the performance of agents and of the system. In this paper we discuss when a distributed system can dynamically change its distribution layout. Our focus is on a distributed environment in which mobile agents move around and are aware of the distributed nature of the system. Changes to the layout of the distribution are not only triggered by the agents (like other, application-specific actions), but they can also be triggered by external events and the environment itself. A layer of meta-agents monitors those triggers. It has the ability to pro-actively change the distribution layout over the different hosts when this improves the behavior and efficiency of the application. Using a specific application (solving distributed constraint satisfaction problems) as an example, we indicate the usefulness of changes to the distribution layout and how they can be incorporated easily into a multiagent application design. It turns out that for some problems, the improvement in efficiency can be more than 30%. [ABSTRACT FROM AUTHOR]

Programming applications for highly dynamic environments such as mobile ad hoc networks (MANETs) is complex, since the working context of applications changes continuously. This paper presents "views" as abstractions for representing and maintaining context information, tailored to applications in MANETs. An application agent can define a view by declaratively describing the context information it is interested in. A supporting middleware platform, called ObjectPlaces, ensures that the information represented by a view continuously reflects the agent's context information, despite the dynamic situation in a MANET. We elaborate on the distributed protocol that ObjectPlaces uses to maintain the information of views, and give an evaluation of the protocol's correctness and overhead. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a policy-driven approach for building and managing large scale agent based systems. We identify different classes of policies for agent based component integration. We also identify the system services and mechanisms that are required for policy-driven integration of components and their management. Policies are derived from the application level requirements and are used in dynamic configuration of agent based systems. Through case studies of two applications we demonstrate the utility of the policy-driven component integration approach in distributed agent systems. [ABSTRACT FROM AUTHOR]

It is generally accepted that the environment is an essential compound of multiagent systems (MASs). Yet the environment is typically assigned limited responsibilities, or even neglected entirely, overlooking a rich potential for the paradigm of MASs. Opportunities that environments offer, have mostly been researched in the domain of situated MASs. However, the complex principles behind the concepts and responsibilities of the environment and the interplay between agents and environment are not yet fully clarified. In this paper, we first give an overview of the state-of-the-art on environments in MASs. The survey discusses relevant research tracks on environments that have been explored so far. Each track is illustrated with a number of representative contributions by the research community. Based on this study and the results of our own research, we identify a set of core concerns for environments that can be divided in two classes: concerns related to the structure of the environment, and concerns related to the activity in the environment. To conclude, we list a number of research challenges that, in our opinion, are important for further research on environments for MAS. [ABSTRACT FROM AUTHOR]

A clear terminology is essential in every research discipline. In the context of ESOA, a lot of confusion exists about the meaning of the terms emergence and self-organisation. One of the sources of the confusion comes from the fact that a combination of both phenomena often occurs in dynamical systems. In this paper a historic overview of the use of each concept as well as a working definition, that is compatible with the historic and current meaning of the concepts, is given. Each definition is explained by supporting it with important characteristics found in the literature. We show that emergence and self-organisation each emphasise different properties of a system. Both phenomena can exist in isolation. The paper also outlines some examples of such systems and considers the combination of emergence and self-organisation as a promising approach in complex multi-agent systems. [ABSTRACT FROM AUTHOR]

Engineering non-trivial open multi-agent systems is a challenging task. Our research focusses on situated multi-agent systems, i.e. systems in which agents are explicitly placed in an environment which agents can perceive and in which they can act. Situated agents do not use long-term planning to decide what action sequence should be executed, but select actions based on the locally perceived state of the world and limited internal state. To cope with change and dynamism of the system, situated agents must be able to adapt their behavior. A well-known family of agent architectures for adaptive behavior are free-flow architectures. However, building a free-flow architecture based on an analysis of the problem domain is a quasi-impossible job for non-trivial agents. To tackle the complexity of designing adaptive agent behavior based on a free-flow architecture, suitable abstractions are needed to describe and structure the agent behavior. The abstraction of a role is obviously essential in this respect. A modeling language is needed as well to model the behavior of the agents. We propose a statechart modeling language to support the design of roles for situated agents. In this paper we describe a design process for adaptive behavior of situated agents as part of a multi-agent oriented methodology. The design process integrates the abstraction of a role with a free-flow architecture. Starting from the results of analysis of the problem domain, the designer incrementally refines the model of the agent behavior. The resulting class diagram serves as a basis for implementation. We illustrate the subsequent design steps with a case study on controlling a collection of automated guided vehicles. [ABSTRACT FROM AUTHOR]

Architectural design plays a key role in software engineering. The software architecture is the backbone of the designed solution, it has the functional requirements of the system and satisfies the quality requirements. In our research, we put forward situated multiagent systems (situated MAS) as an approach to build distributed applications with demanding quality requirements such as flexibility and openness. In this paper we illustrate how we apply situated MAS to an Automatic Guided Vehicle (AGV) transportation system. We discuss the high-level structure of the software architecture and explain how the architecture aims to meet important quality requirements. [ABSTRACT FROM AUTHOR]

Time management is essential when simulating multi-agent systems (MASs) as it allows consistent and repeatable simulation runs. So far, time management lacks support to express the timing requirements of a simulation explicitly and at an abstraction level appropriate for MAS developers. Moreover, integrating time management into a MAS requires the developer to alter the design of the MAS. In this paper, we first propose semantic duration models to capture timing requirements that reflect the semantics of MAS activities in an explicit model. Second, we present a time management infrastructure that starts from a semantic duration model description to integrate all time management functionality into a MAS transparently, i.e. without requiring the developer to alter the design of the MAS. We use aspect-oriented programming technology as it allows separation of concerns, a crucial software engineering requirement. As a case, we apply our approach to the Packet-World. [ABSTRACT FROM AUTHOR]

This paper presents a model for adaptive agents. The model describes the behavior of an agent as a graph of roles, in short a behavior graph. Links between roles provide conditions that determine whether the agent can switch roles. The behavior graph is assigned at design time, however adaptive role selection takes place at runtime. Adaptivity is achieved through factors in the links of the behavior graph. A factor models a property of the agent or its perceived environment. When an agent can switch roles via different links, the factors determine the role the agent will switch to. By analyzing the effects of its performed actions the agent is able to adjust the value of specific factors, adapting the selection of roles in line with the changing circumstances. Models for adaptive agents typically describe how an agent dynamically selects a behavior (or action) based on the calculation of a probability value as a function of the observed state for each individual behavior (or action). In contrast, the model we propose aims to dynamically adapt logical relations between different behaviors (called roles here) in order to dynamically form paths of behaviors (i.e. sequences of roles) that are suitable in the current state. To verify the model we applied it to the Packet-World. In the paper we discuss simulation results that show how the model enables the agents in the Packet-World to adapt their behavior to changes in the environment. [ABSTRACT FROM AUTHOR]

So far, the main focus of research on adaptability in multi-agent systems (MASs) has been on the agents' behavior, for example on developing new learning techniques and more flexible action selection mechanisms. In this paper, we introduce a different type of adaptability in MASs, called time management adaptability. Time management adaptability focuses on adaptability in MASs with respect to execution control. First, time management adaptability allows a MAS to be adaptive with respect to its execution platform, anticipating arbitrary and varying timing delays which can violate correctness. Second, time management adaptability allows the execution policy of a MAS to be customized at will to suit the needs of a particular application. We discuss the essential parts of time management adaptability: (1) we employ time models as a means to explicitly capture the execution policy derived from the application's execution requirements, (2) we classify and evaluate time management mechanisms which can be used to enforce time models, and (3) we introduce a MAS execution control platform which combines both previous parts to offer high-level execution control. [ABSTRACT FROM AUTHOR]