10550445
Fuzzy Bayesian Networks - A General Formalism for Representation, Inference and Learning with Hybrid Bayesian Networks
This paper proposes a general formalism for representation, inference and learning with general hybrid Bayesian networks in which continuous and discrete variables may appear anywhere in a directed acyclic graph. The formalism fuzzifies a hybrid Bayesian network into two alternative forms: the first form replaces each continuous variable in the given directed acyclic graph (DAG) by a partner discrete variable and adds a directed link from the partner discrete variable to the continuous one. The mapping between two variables is not crisp quantization but is approximated (fuzzified) by a conditional Gaussian (CG) distribution. The CG model is equivalent to a fuzzy set but no fuzzy logic formalism is employed. The conditional distribution of a discrete variable given its discrete parents is still assumed to be multinomial as in discrete Bayesian networks. The second form only replaces each continuous variable whose descendants include discrete variables by a partner discrete variable and adds a directed link from that partner discrete variable to the continuous one. The dependence between the partner discrete variable and the original continuous variable is approximated by a CG distribution, but the dependence between a continuous variable and its continuous and discrete parents is approximated by a conditional Gaussian regression (CGR) distribution. Obviously, the second form is a finer approximation, but restricted to CGR models, and requires more complicated inference and learning algorithms. This results in two general approximate representations of a general hybrid Bayesian networks, which are called here the fuzzy Bayesian network (FBN) form-I and form-II. For the two forms of FBN, general exact inference algorithms exists, which are extensions of the junction tree inference algorithm for discrete Bayesian networks. Learning fuzzy Bayesian networks from data is different from learning purely discrete Bayesian networks because not only all the newly converted discrete variables are latent in the data, but also the number of discrete states for each of these variables and the CG or CGR distribution of each continuous variable given its partner discrete parents or both continuous and discrete parents have to be determined.
24019518
Obtaining the service language for H.245's multimedia capability exchange signalling protocol: the final step
The capability exchange signalling (CES) protocol is a subprotocol of ITU-T recommendation H.245, "control protocol for multimedia communication". We are interested in verifying this protocol, including verification of its general properties such as absence of deadlocks and livelocks, and verification of the protocol against its service. In previous work, we have analysed the general properties of the CES protocol. In order to verify the protocol against its service, we need to generate the CES service language, which defines all the possible sequences of user observable events. We firstly create the CES service CPN model and then extract the language from the occurrence graph (OG) of the model. In the case of the CES service, this is challenging because we wish to have a general result for arbitrary capacity of the network over which the CES protocol operates. To tackle this problem we introduced into the CPN model a parameter, l, representing the capacity of the communication channel. We derived a recursive formula for the parameterised OG in terms of l. We treat this OG as a finite state automaton (FSA) by nominating acceptance states and apply FSA reduction algorithms to obtain a deterministic FSA that represents the CES service language. We have discovered a recursive formula in l for the CES service language. This paper introduces the CES service via its CPN model as necessary background and presents the final step of the proof of this finding.
42350068
Tackling the Infinite State Space of a Multimedia Control Protocol Service Specification
Coloured Petri Nets (CPNs) are used to model the service provided by an International Standard for the control of multimedia communications over telecommunication networks including the Internet, known as the Capability Exchange Signalling (CES) protocol. The state space of the CPN model includes all of the possible sequences of user observable events, known as the service language, which is a useful baseline against which the protocol can be verified. However, the CES service CPN possesses an infinite state space, due to unbounded communication channels. We parameterize the CPN with the channel capacity, propose and prove a recursive formula for its state space and provide an algorithm for its construction. The algorithm generates the state space for capacity l, from the state space for capacity l - 1, providing incremental state space generation rather than generating a new state space for each value of l. The state space is linear in the size of the channel.
694549
Optimizing Multiple Distributed Stream Queries Using Hierarchical Network Partitions
We consider the problem of query optimization in distributed data stream systems where multiple continuous queries may be executing simultaneously. In order to achieve the best performance, query planning (such as join ordering) must be considered in conjunction with deployment planning (e.g., assigning operators to physical nodes with optimal ordering). However, such a combination involves not only a large number of network nodes but also many query operators, resulting in an extremely large search space for optimal solutions. Our paper aims at addressing this problem by utilizing hierarchical network partitions. We propose two algorithms - top-down and bottom-up which utilize hierarchical network partitions to provide scalable query optimization. Formal analysis is presented to establish the bounds on the search-space and to show the sub-optimality of our algorithms. Through simulations and experiments using a prototype deployed on Emulab we demonstrate the effectiveness of our algorithms.
47117005
A reputation-based trust model for peer-to-peer e-commerce communities
Peer-to-peer e-commerce (electronic commerce) communities are commonly perceived as an environment offering both opportunities and threats. One way to minimize threats in such an open community is to use community-based reputations to help evaluating the trustworthiness and predicting the future behavior of peers. We present PeerTrust - a coherent adaptive trust model for quantifying and comparing the trustworthiness of peers based on a transaction-based feedback system. There are two main features of our model. First, we introduce three basic trust parameters in computing trustworthiness of peers. In addition to feedback a peer receives through its transactions with other peers, we incorporate the total number of transactions a peer performs, and the credibility of the feedback sources into the model for evaluating the trustworthiness of peers. We argue that the trust models based solely on feedback from other peers in the community are inaccurate and ineffective. Second, we introduce two adaptive trust factors, the transaction context factor and the community context factor, to allow the basic trust metric to incorporate different contexts (situations) and to address common problems encountered in a variety of online e-commerce communities. We present a concrete method to validate the proposed trust model and report the set of simulation-based experiments, showing the feasibility and benefit of the PeerTrust model.
8242993
Designing Web-Based Systems in Social Context: A Goal and Scenario Based Approach
In order to design a better web-based system, a designer would like to have notations to visualize how design experts’ know-how can be applied according to one’s specific social and technology situation. We propose the combined use of a goal-oriented language GRL and a scenarios-oriented notation UCM for representing design knowledge of web-based systems and information systems in general. Goals are used to depict business objectives, functional and non-functional system requirements. Tasks are used in the exploration of alternative technologies and their operationalizations into system constructs. Actors are used to do role-based analysis on social relationships. Scenarios are used to describe elaborated business processes or workflow. The approach is illustrated with an example of designing a web-based training system.
18178349
TAM: a system for dynamic transactional activity management
Electronic commerce (EC) has remarkably reshaped today's business practices. The logic embedded in business transactions are becoming more exible and sophisticated; the number of components within these business transactions are fastly increasing; and business transactions are getting more distributed and interactive as well. These, on the other hand, make today's business applications more vulnerable to resource availability constraints and consistency problems due to failures. For example, network congestion, server overload, user absence, and other exceptions all might cause temporary or permanent bottlenecks to ongoing business work ows. Developing system support to make work ow activities more reliable, e cient, and adaptive to changes or exceptions therefore poses important yet challenging questions that call for practical solutions. The TAM project at OGI aims at developing a exible framework and algorithms that address these challenges. Comparing with other research e orts, our approach is unique in that we combine advanced transaction processing (TP) technologies with adaptive methods to guide our system design, and build the mechanisms by extending the functions of current TP systems. On the theoretical side, we have developed a Transactional Activity Model (TAM) for the speci cation and management of activities with transactional properties. TAM is a careful combination of a compositional activity model [5] with well-de ned extended transaction models (ETMs) [3] such as split/join transactions [9]. It provides simple and effective speci cation facilities that allow business process designers to specify the behavioral composition and re nement
2383268
Efficient Formation of Edge Cache Groups for Dynamic Content Delivery
Cost-effective cooperation among a network of edge caches is widely accepted as an effective mechanism for enhancing the scalability, performance, and reliability of edge cache networks. However, the problem of how to form cache groups for achieving effective and efficient cooperation in edge cache networks has largely been unexplored. In this paper, we identify two important factors that need to be considered while forming cooperative groups, namely, network proximities of edge caches and network distances of the caches to the origin server. We propose two novel cache clustering schemes for accurately partitioning the caches of a given edge cache network into specified number of cache groups. The first scheme, called the Selective Landmarks scheme (SL scheme), accurately partitions the edge cache network into cooperative groups based on the network proximities of the caches. The second cache group formation scheme, called Server Distance sensitive Selective Landmarks scheme (SDSL scheme), provides a careful combination network proximities and server distances. Our experiments indicate that the proposed techniques can yield significant performance benefits.