Alessio Botta

Context adaptation of fuzzy systems through a multi-objective evolutionary approach based on a novel interpretability index

Context adaptation (CA) based on evolutionary algorithms is certainly a promising approach to the development of fuzzy rule-based systems (FRBSs). In CA, a context-free model is instantiated to a context-adapted FRBS so as to increase accuracy. A typical requirement in CA is that the context-adapted system maintains the same interpretability as the context-free model, a challenging constraint given that accuracy and interpretability are often conflicting objectives. Furthermore, interpretability is difficult to quantify because of its very nature of being a qualitative concept. In this paper, we first introduce a novel index based on fuzzy ordering relations in order to provide a measure of interpretability. Then, we use the proposed index and the mean square error as goals of a multi-objective evolutionary algorithm aimed at generating a set of Pareto-optimum context-adapted Mamdani-type FRBSs with different trade-offs between accuracy and interpretability. CA is obtained through the use of specifically designed operators that adjust the universe of the input and output variables, and modify the core, the support and the shape of fuzzy sets characterizing the partitions of these universes. Finally, we show results obtained by using our approach on synthetic and real data sets.

A genetic approach to joint routing and link scheduling for wireless mesh networks

Wireless mesh networks are an attractive technology for providing broadband connectivity to mobile clients who are just on the edge of wired networks, and also for building self-organized networks in places where wired infrastructures are not available or not deemed to be worth deploying. This paper investigates the joint link scheduling and routing issues involved in the delivery of a given backlog from any node of a wireless mesh network towards a specific node (which acts as a gateway), within a given deadline. Scheduling and routing are assumed to be aware of the physical interference among nodes, which is modeled in the paper by means of a signal-to-interference ratio. Firstly, we present a theoretical model which allows us to formulate the task of deriving joint routing and scheduling as an integer linear programming problem. Secondly, since the problem cannot be dealt with using exact methods, we propose and use a technique based on genetic algorithms. To the best of our knowledge, these algorithms have never been used before for working out these kinds of optimization problems in a wireless mesh environment. We show that our technique is suitable for this purpose as it provides a good trade-off between fast computation and the overall goodness of the solution found. Our experience has in fact shown that genetic algorithms would seem to be quite promising for solving more complex models than the one dealt with in this paper, such as those including multiple flows and multi-radio multi-channels.

A fuzzy approach for negotiating quality of services

A central point when integrating services concerns to the description, agreement and enforcement of the quality aspect of service interaction, usually known as Service Level Agreement (SLA). This paper presents a framework for SLA negotiation based on fuzzy sets.We propose (i) a request language for clients to describe quality preferences, (ii) a publication language for providers to define the qualities of their offered services, and (iii) a decision procedure for granting any client request with a SLA contract fitting the requestor requirements. We start with a restricted framework in which the different qualities of a service are handled independently (as being orthogonal) and then we propose an extension that allows clients and providers to express dependencies among different qualities.

Joint Routing and Link Scheduling for Wireless Mesh Networks through Genetic Algorithms

Wireless mesh networks (WMN) are emerging as an attractive technology for providing broadband connectivity to mobile clients who are just on the edge of wired networks, and also for building self-organized networks in places where wired infrastructures are not available or not deemed to be worth deploying. This paper investigates the joint link scheduling and routing issues involved in the delivery of a given backlog from any node of a WMN towards a specific node (which acts as a gateway), within a given deadline. As in a real WMN, scheduling and routing are assumed to be aware of the physical interference among nodes, which is modeled in the paper by means of a signal-to-interference ratio (SIR). Firstly, using a theoretical model of a WMN we formulate the problem as an integer linear programming (ILP) problem. Secondly, since the problem cannot be dealt with using exact methods, we propose and use a technique based on genetic algorithms (GAs). To the best of our knowledge, GAs have never been used before for working out these kinds of optimization problems in a WMN environment. We show that our technique is suitable for this purpose as it provides a good trade-off between fast computation and the overall goodness of the solution found. Our experience has in fact shown that GAs would seem to be quite promising for solving more complex WMN models than the one dealt with in this paper, such as those including multiple flows and multi-radio multi-channels.

Context Adaptation of Mamdani Fuzzy Systems through New Operators Tuned by a Genetic Algorithm

Context adaptation can be achieved by adjusting an initial normalized fuzzy rule-based system through the use of operators that appropriately change the representation of the linguistic variables. The choice of the specific operators and their parameters should be context-based and optimized so as to obtain a good interpretability-accuracy tradeoff. In this paper we propose a set of context adaptation operators that, starting from a given fuzzy system, adjust some of its component!, such as fuzzy set support and core, membership function shape, etc. We use a genetic tuning process for choosing the operator parameters. We finally describe the application of the proposed operators to Mamdani fuzzy systems with reference to two real examples.

Exploiting Fuzzy Ordering Relations to Preserve Interpretability in Context Adaptation of Fuzzy Systems

In the framework of context adaptation of fuzzy systems, a typical requirement of a contextualized system is to maintain the same interpretability as the original one. Here, we propose a novel index based on a fuzzy ordering relation to provide a measure of interpretability. Our index assesses ordering, distinguishability and coverage at the same time. We use the proposed index and the mean square error as goals of a multi-objective genetic algorithm aimed at generating contextualized Mamdani fuzzy systems with different trade-offs between the two goals. Results obtained on a synthetic data set are also discussed.

Evaluation of Various Interference Models for Joint Routing and Scheduling in Wireless Mesh Networks

We explore radio resource allocation in wireless mesh networks, namely we study how to determine a space- and time-division pattern of transmissions, to deliver traffic to gateway nodes. We highlight link scheduling and routing issues, which we investigate in a cross-layer framework. To this end, an integer linear program is presented, where diverse constraints affect resource allocation; in particular, we focus in this paper on the key role played by the characterization of radio interference. Finally, we obtain numerical results through a genetic algorithm, and we are able to show that the wireless interference model adopted strongly affects the performance of the radio resource allocation; thus, an accurate representation of the wireless channel is necessary to obtain meaningful results.

Integrating service-oriented technologies to support business processes

In this paper we present a case example of how heterogeneous services and technologies can be integrated. We show a service-oriented architecture based on Web services to perform specific operations, issued by distributed processes through different protocols (HTTP, POPS, RMI and SMS), on a particular ERP system, namely the SAP R/3 system. The architecture results from the integration of two different service-oriented technologies: Java message service and SAP Java connector, and uses business process execution language for Web services choreography. We describe a prototype of the proposed architecture and discuss how a sample business operation, consisting of a purchase order input to SAP R/3 from any of a variety of technological devices, can be performed.