Component-oriented programming

Context-awareness is gaining wide importance, especially when targeting pervasive environments, whereas Web Services are often exploited as building blocks of context-aware applications because of their interoperability properties. In this framework, Web Services can be used as business services requiring context data for their functionality, but also as context sources offering access to context information. Combining the development of context-aware Web Services with Model-Driven Engineering techniques requires the identification and matching of appropriate context models with Web Service models. In this paper, a new ongoing research direction is presented, which refers to model transformation for allowing the identification of appropriate context sources and ensuring their compatibility with Web Services. Matchmaking principles between Web Service and context models are examined in order to extract a reasoning mechanism on context adaptation compatibility. In specific, the principles of graph transformation are mainly exploited.

The recent approaches for Web services composition tend to integrate heterogeneous business processes executed in Peer-to-Peer networks. In such networks, component Web services are invoked on independent peers and are orchestrated according to the transactional requirements defined by the designers or the users of the composite Web service. Since component Web services can be dynamically invoked and are generally implemented as black boxes, concurrency between them may appear. This paper presents the transactional execution model of composite Web services exploiting the transactional properties of their component Web services. The proposed concurrency control is ensured by a decentralized serialization graph based on an optimistic protocol and on the hierarchical structure of the composition. The globally correct execution of the composite Web service is achieved by communication among dependent subtrans-actions and the peers they have accessed.

In the Grid environment, user can manage and make use of web services, such as uploading or downloading web services. But when user wants to download one web services to run it in a local machine, one problem may occur: The web service can only be run on a special operating system, which is not the operating system that the user operates. To solve this problem, we need construct one middleware to emulate the running environment of the web service in the operating system that user operates. Middleware is the component created by the Operation System according to its metadata, and it is also the center from which the Internet technology extended. Component-based middleware has emerged as an important architectural component in modern distributed systems, such as XPCOM, UNO and the CORBA Component Model. Java Virtual Machine (JVM) is a middleware, aimed at making application cross platform to run. The goal of our research is to extend this work in order to exploit one component-based middleware platform that can make web services to run on different operating system platforms, such as Elastos, Windows and Linux operating system. In this paper, a new and efficient component model based on COM (ezCOM) is proposed. More specifically, this paper describes in detail how ezCOM can be used to construct a full component-based crossing Operating system middleware platform and also puts forward one new measure model to compare the performance of ezCOM, Wine-COM, XPCOM and UNO.

The presented paper describes a promising approach of adaptive deployment in CORBA Component Model (CCM). Adaptation, as an essential concept of contemporary distributed systems, is used to improve planning of component deployment. There is described a concept and implementation of mechanisms which, using monitoring infrastructure and simple policy-based engine, allows improving execution efficiency. The presented tool, named CCMAD, is intended for use with OpenCCM platform, an open source Java implementation of CCM model. It is, however, expected that adapting CCMAD for any other CCM platform would not be troublesome.

While Web service models become increasingly popular and many service providers start to offer all kinds of Web services, the quality of service (QoS) for Web services has become an important factor for service requesters to consider during the selection process of appropriate Web services. In this paper, we present an evaluation and selection framework (CosmosQoS) for QoS-required Web services. A novel architecture and reputation appraisal model to monitor, store and evaluate the physical usage and post-condition of requested Web services in a requester-located network is proposed to better support service requesters such that they can select suitable Web services based on their QoS requirements, trustworthiness of Web services, and effect of network connection and configuration between service requesters and providers.

Component-based programming models are well-suited to the design of large-scale, distributed applications because of the ease with which distributed functionality can be developed, deployed, and validated using the models' compositional properties. Existing component models supported by standardized technologies, such as the OMG's CORBA Component Model (CCM), however, incur a number of limitations in the context of cyber physical systems (CPS) that operate in highly dynamic, resource-constrained, and uncertain environments, such as space environments, yet require multiple quality of service (QoS) assurances, such as timeliness, reliability, and security. To overcome these limitations, this paper presents the design of a novel component model called F6COM that is developed for applications operating in the context of a cluster of fractionated spacecraft. Although F6COM leverages the compositional capabilities and port abstractions of existing component models, it provides several new features. Specifically, F6COM abstracts the component operations as tasks, which are scheduled sequentially based on a specified scheduling policy. The infrastructure ensures that at any time at most one task of a component can be active - eliminating race conditions and deadlocks without requiring complicated and error-prone synchronization logic to be written by the component developer. These tasks can be initiated due to (a) interactions with other components, (b) expiration of timers, both sporadic and periodic, and (c) interactions with input/output devices. Interactions with other components are facilitated by ports. To ensure secure information flows, every port of an F6COM component is associated with a security label such that all interactions are executed within a security context. Thus, all component interactions can be subjected to Mandatory Access Control checks by a Trusted Computing Base that facilitates the interactions. Finally, F6COM provides capabilities to monitor task execution deadlines and to configure component-specific fault mitigation actions.

Commercial off-the-shelf (COTS) middleware is now widely used to develop distributed real-time and embedded (DRE) systems. DRE systems are themselves increasingly combined to form "systems of systems" that have diverse quality of service (QoS) requirements. Earlier generations of COTS middleware, such as Object Request Brokers (ORBs) based on the CORBA 2.x standard, did not facilitate the separation of QoS policies from application functionality, which made it hard to configure and validate complex DRE applications. The new generation of component middleware, such as the CORBA Component Model (CCM) based on the CORBA 3.0 standard, addresses the limitations of earlier generation middleware by establishing standards for implementing, packaging, assembling, and deploying component implementations. There has been little systematic empirical study of the performance characteristics of component middleware implementations in the context of DRE systems. This paper therefore provides four contributions to the study of CCM for DRE systems. First, we describe the challenges involved in benchmarking different CCM implementations. Second, we describe key criteria for comparing different CCM implementations using key black-box and white-box metrics. Third, we describe the design of our CCMPerf benchmarking suite to illustrate test categories that evaluate aspects of CCM implementation to determine their suitability for the DRE domain. Fourth, we use CCMPerf to benchmark CIAO implementation of CCM and analyze the results. These results show that the CIAO implementation based on the more sophisticated CORBA 3.0 standard has comparable DRE performance to that of the TAO implementation based on the earlier CORBA 2.x standard.

Towards a context-based multi-type policy approach for Web services composition

Component middleware technologies such as the CORBA component model (CCM), J2EE (Alur et al., 2001), and .NET, were developed to address many limitations like interdependencies between services and object interfaces, limited re-use, of first-generation middleware technologies such as CORBA 2.x, XML, and SOAP (Snell and McLeod, 2001). These component technologies have addressed a wide range of application domains, but unfortunately for distributed real-time and embedded (DRE) systems, the focus of these technologies has been primarily on functional and not quality of service (QoS) properties. Research on QoS-aware component models such as the CIAO project (Wang et al. 2003) shows that there is a fundamental difference between configuration of functional and QoS properties even within such a unified component model: the dominant decomposition of functional properties is essentially object-oriented, while the dominant decomposition of QoS properties is essentially aspect-oriented. In this paper, we describe how a focus on aspect frameworks for configuring QoS properties both complements and extends QoS-aware component models. This paper makes three main contributions to the state of the art in DRE systems middleware. First, it describes a simple but representative problem for configuring QoS aspects that cut across architectural layers, system and distribution boundaries, which motivates our focus on aspect frameworks. Second, it provides a formalization of that problem using first order logic nfrastructure configuration logic - which both guides the design of aspect configuration infrastructure, and offers a way to connect these techniques with model-integrated computing (Ledeczi et al. 2001) approaches to further reduce the programming burden on DRE system developers. Third, it describes alternative mechanisms to ensure correct configuration of the aspects involved, and notes the phases of the DRE system lifecycle at which each such configuration mechanism is most appropriate.

Users of Web and grid services often must temporarily delegate some or all of their rights to a software entity to perform actions on their behalf. The problem with the typical grid services approach (X. 509 proxy certificates) is that commercial Web services tooling fails to recognize these certificates or process them properly. The security assertion markup language (SAML) is a standardized XML-based framework for exchanging authentication, authorization and attribute information. SAML has broadening commercial support but lacks delegation capabilities. To address this shortcoming, we exploit SAML's inherent extensibility to create a delegation framework for Web and grid services that supports both direct and indirect delegation. We develop a set of verification rules for delegation tokens that rely on WS-Security X.509 signatures, but do not force any trust relationship between the delegatee and the target service. We have implemented the framework on two common Web service hosting environments: Java/Tomcat and .NET. By leveraging existing Web services standards, we make it easier for Grid practitioners to build and consume Web and grid services without resorting to grid-specific protocols.

Some current implementations of CORBA Component Model (CCM) are flawed with unreasonable communication overheads when components are in the same address space and in the same container. Alternative approaches have introduced mechanisms for direct local communication of such components. In these approaches collocated components do not communicate through ORB and therefore cannot use ORB services such as events, naming and transactions locally, unless they are programmed explicitly. This paper presents a new approach for communication of collocated components with local ORB-like services support. A unit inside each container is responsible for handling communication between components within or outside the container. Local requests are passed to the local components without ORB involvement. Local or remoteness of a request is determined from the IOR of the called component which has been logged by the relevant special unit upon the creation of the component in its container. Implementation results of our approach show a considerable reduction of local communication overheads.

Web Services offer a platform independent solution for system integration in a distributed environment. But Web Services are weak in representing the business semantics of application domains. This paper presents a model-driven approach for specifying domainspecific component models in an effort to complement the current Web Services technology in terms of enriching the semantics representation. Web Services Description Language (WSDL) can then be generated automatically from the models with generators. The modeling of domain-specific components serves as a front-end to represent the semantics of components as well as for formalizing components while the generated artifacts facilitate component service synthesis.

The automatic composition of Web services requires the existing services to be encoded in a semantic form, such as ontology. If Web services are represented with ontology, we can automatic compose Web services by means of their semantics. Ontology modeling is divided into two steps: input/output parameters modeling and Web services modeling. First, we collect Web services' input/output parameters, represent them with classes in ontology, and transform Web services to properties in ontology, define relations between classes and properties. Then we judge Web services' relations based on relations between properties transformed from these Web services and estimate whether these Web services can be composed.

In the past few years, the multi-agent systems (MAS) area has presented an accelerated growth. New techniques and tools are constantly being proposed and several methodologies have been published to support the development of MAS. Most of these methodologies concentrate on the system analysis phase, giving almost no support for MAS implementation. Since agents can be seen as sort of specialized distributed components, in this paper we propose an agent deployment model based on the CORBA Component Model. We also describe a case study to show the potential of an agent-based application development using this model.

The increasing popularity of Web services for application integration has strengthened the need for automated Web service composition and joint execution. A lot of attention has been paid recently towards techniques for creating a composite Web service from individual Web services based on user requirements, and driven by a variety of criteria. However, the major lacuna so far in Web service composition is the lack of a holistic requirements-driven approach for modeling the Web service execution lifecycle. In this paper we present such an approach based on our earlier work on context-driven Web service modeling. In particular, we separate requirements into two parts - functional and extrafunctional requirements (FRs and EFRs, respectively). We express FRs as commitments made by individual Web ser-vices towards the composite Web service, and EFRs as rules that constrain the behavior of the individual Web services while they execute against their FRs. We also present a conceptual model that can be used for tracking requirements during Web service execution.