Many reputation management systems have been developed under the assumption that each entity in the system will use a variant of the same scoring function. Much of the previous work in reputation management has focused on providing robustness and improving performance for a given reputation scheme. In this paper, we present a reputation-based trust management framework that supports the synthesis of trust-related feedback from many different entities while also providing each entity with the flexibility to apply different scoring functions over the same feedback data for customized trust evaluations. We also propose a novel scheme to cache trust values based on recent client activity. To evaluate our approach, we implemented our trust management service and tested it on a realistic application scenario in both LAN and WAN distributed environments. Our results indicate that our trust management service can effectively support multiple scoring functions with low overhead and high availability.

Service composition has emerged as a fundamental technique for developing Web applications. Multiple services, often from different organizations or trust domains, may be dynamically composed to satisfy a user's request. Access control in the presence of service compositions is a challenging security problem. In this paper, we present an access control model and techniques for specifying and enforcing access control rules on Web service compositions. A key advantage of our approach is that past histories of service invocations can be used to make access control decisions. Our approach allows role hierarchies and separation of duty constraints. Access controls rules may be parameterized by one or more arguments. We have implemented our access control model via a declarative policy specification language which uses pure-past linear temporal logic (PPLTL). We describe an implementation of our approach using a supply chain management (SCM) application. Our experiments show that our approach can enforce expressive and flexible access control policies while incurring reasonable performance overhead on the application.

A major goal of service-oriented architectures is to enable software interoperability in heterogeneous and dynamic environments. Web services standards and protocols aim to support this goal and middleware systems implementing these standards and protocols consequently are needed. Maintenance and administration of middleware is made difficult due to variations in standards and their constant evolution. In this paper, we introduce a new service-oriented middleware architecture for runtime Web services interoperability. Different from other middleware systems our approach applies service-oriented computing principles on the middleware layer, thereby establishing an on-demand model for middleware features. Clients can use middleware as services, dynamically discovering and using the services as interoperability requirements are determined. Further, middleware as services allows middleware to be provided and managed separately from its clients. We present the policy-based programming model, architecture, and details of our middleware, and discuss new challenges that arise in this context, such as distribution of middleware services. The approach is validated through a scenario integrating Web service transaction middleware

Distributed applications composed of collections of Web services may call for diverse levels of reliability in different parts of the system. Byzantine fault tolerance (BFT) is a general strategy that has recently been shown to be practical for the development of certain classes of survivable, client-server, distributed applications; however, little research has been done on incorporating it into selective parts of multi-tier, distributed applications like Web services that have heterogeneous reliability requirements. To understand the impacts of combining BFT and Web services, we have created Thema, a new BFT middleware system that extends the BFT and Web services technologies to provide a structured way to build Byzantine-fault-tolerant, survivable Web services that application developers can use like other Web services. From a reliability perspective, our enhancements are also novel in that they allow Byzantine-fault-tolerant services: (1) to support the multi-tiered requirements of Web services, and (2) to provide standardized Web services support for their own clients (through WSDL interfaces and SOAP communication). In this paper we study key architectural implications of combining BFT with Web services and provide a performance evaluation of Thema using the TPC-W benchmark.

A holy grail of component-based software engineering is write-once, reuse everywhere. However, in modern distributed, component-based systems supporting emerging application areas such as service-oriented e-business (where Web services are viewed as components) and peer-to-peer computing, this is difficult. Non-functional requirements (related to quality-of-service (QoS) issues such as security, reliability, and performance) vary with deployment context, and sometimes even at run-time, complicating the task of re-using components. In this paper, we present a middleware-based approach to managing dynamically changing QoS requirements of components. Policies are used to advertise non-functional capabilities and vary at run-time with operating conditions. We also provide middleware enhancements to match, interpret, and mediate QoS requirements of clients and servers at deployment time and/or runtime.

Standard messaging middleware guarantees the delivery of messages to intermediary destinations like message queues, but does not guarantee the receipt or the processing of a message by final recipients. Conditional messaging is an extension to standard messaging middleware that addresses this shortcoming by allowing an application to define, monitor, and evaluate various conditions on messages, such as time constraints on the receipt or the processing of a message by a set of final recipients. In this paper, we introduce the notion of conditional messaging, and present the design and implementation of a flexible and reliable system that supports conditional messaging for use in Java 2 Enterprise Edition and message queuing environments. Our solution uniquely shifts the responsibilities for implementing the management of conditions on messages from the application to the middleware. We further discuss the grouping of multiple conditional messages into atomic units-of-work, which can also integrate requests to transactional resources like distributed objects using object middleware. Conditional messaging serves to implement various kinds of backward dependencies for distributed object transactions that integrate messaging.

Many enterprise systems employ both object-oriented middleware (OOM) and message-oriented middleware (MOM). However support for the integration of object and messaging services, in particular for transaction processing across object and messaging components, is very limited. In this paper we introduce the concept of Dependency-Spheres (D-Spheres), a global transaction context for distributed objects and messages. A D-Sphere integrates standard distributed object transactions and conditional asynchronous messages in one single unit-of-work. It is a new service for transaction processing that enhances two-phase-commit ACID transactions with pre-commit message delivery, concurrent evaluations of transaction-critical message conditions, and message compensation support for recovery. D-Spheres enrich standard OOM and MOM services, uniquely providing for an increased level of reliability for their use in combination in enterprise systems.