Mubarak Mohammad

Publishing and discovering context-dependent services

In service oriented computing, service providers and service requesters are main interacting entities. A service provider publishes the services it wishes to make public using service registries. A service requester initiates a discovery process to find the service that meets its requirements using the service registries. Current approaches for the publication and discovery do not realize the essential relationship between the service contract and the conditions in which the service can guarantee its contract. Moreover, they do not use any formal methods for specifying services, contracts, and compositions. Without a formal basis it is not possible to justify through a rigorous verification the correctness conditions for service compositions and the satisfaction of contractual obligations in service provisions. In our recent works, we have identified the role of contextual information, trustworthiness information and legal rules in service provision. This paper focuses on the publication and discovery of trustworthy context-dependent services as supported by the novel framework FrSeC. It introduces a novel ranking algorithm that ranks trustworthy context-dependent services according to the degree they match service requesters requirements. Finally, this paper introduces a prototype implementation for the matching and ranking of services as supported by FrSeC.

A formal approach for the specification and verification of trustworthy component-based systems

Abstract: Software systems are increasingly becoming ubiquitous affecting the way we experience the world. Embedded software systems, especially those used in smart devices, have become an essential constituent of the technological infrastructure of modern societies. Such systems, in order to be trusted in society, must be proved to be trustworthy. Trustworthiness is a composite non-functional property that implies safety, timeliness, security, availability, and reliability. This paper presents a formal approach for the development of trustworthy component-based systems. The approach involves a formal component model for the specification of components structure, functional, and non-functional (trustworthiness) properties, a model transformation technique for the automatic generation of component behavior using the specified structure and restricted by the specified properties, and a unified formal verification method for safety, security, reliability and availability properties using model checking.

TADL - An Architecture Description Language for Trustworthy Component-Based Systems

Existing architecture description languages mainly support the specification of the structural elements of the system under design with either only a limited support or no support to specify non-functional requirements. In a component-based development of trustworthy systems, the trustworthiness properties must be specified at the architectural level. Analysis techniques should be available to verify the trustworthiness properties early at design time. Towards this goal we present in this paper a meta-architecture and TADL, a new architecture description language suited for describing the architecture of trustworthy component-based systems. The TADL is a uniform language for specifying the structural, functional, and nonfunctional requirements of component-based systems. It also provides a uniform source for analyzing the different trustworthiness properties.

A FRAMEWORK FOR DEVELOPING CONTEXT-AWARE SYSTEMS

In ubiquitous computing the environment constraints are often regarded as static and software applications are allowed to function in a mobile ecospace. However, in context-aware systems the environment attributes of software applications are dynamically changing. This dynamism of contexts must be accounted for in order to provide the true intended effect on the application of services. Consequently, context-aware software applications should perceive their context in a continuous manner and seamlessly adapt to it. This thesis investigates the process of constructing context-aware applications and identifies the main challenges in this domain. The two principal requirements are (1) formally defining what context is and expressing the enclosed semantics, (2) formally defining dynamic compositions of adaptations and triggering their responses to changes in the environment context. This thesis proposes a component-based architecture for a Context-aware Framework that would be used to bring awareness capabilities into applications. Two languages are formally designed. One is to formally express situations, leading to a context reasoner, and another is to formally express workflow, leading to timely triggering of reactions and enforcing policies. With these formalisms and a component design that can be formalized, the thesis work fulfills a formal approach to construct context-aware applications. A proof-ofconcept case study is implemented to examine the expressiveness of the framework design and test its implementation.

An Architecture for Managing and Delivering Trustworthy Context-Dependent Services

A precise definition of services is necessary in order to discover, publish, and deliver them. Services, when provided, should satisfy their binding contractual obligations, be seen as trustworthy by the users, and correctly fulfill the needs of the context in which they will be used. The FrSeC architecture proposed in this paper aims to fulfill these needs. The architecture is formally describable, supports the specification, publication, discovery, selection, and composition of services with context-dependent contracts.

Managing and Delivering Trustworthy Context-Dependent Services

Service-oriented architecture (SOA) is emerging as the future of distributed computing and enterprise application development. The two key issues in service-oriented applications should be that every provided service meets the expected trust level set by the service requester, and the provided service satisfies its contract in the context of service provision. In order to enforce these issues, it is necessary to specify in the service its trustworthiness properties, and the relationship between its contracts and the contexts in which it is to be provided. However, current approaches have failed to specify them. The FrSeC architecture proposed in this paper aims to remedy this situation. The architecture supports the specification, publication, discovery, selection, and composition of services, where a service with its functional and nonfunctional aspects is bound to a context-driven contract. A family of Service Provision Specification Languages (SPSL) is introduced to specify the architectural elements. The semantic domain behind SPSL is an abstract architecture description formalism based on set theory and logic. This paper provides an overview of FrSeC framework and gives SPSL descriptions for Service Registry, and Service Requester in FrSeC.

Specification and Verification of Context-dependent Services

Current approaches for the discovery, specification, and provision of services ignore the relationship between the service contract and the conditions in which the service can guarantee its contract. Moreover, they do not use formal methods for specifying services, contracts, and compositions. Without a formal basis it is not possible to justify through formal verification the correctness conditions for service compositions and the satisfaction of contractual obligations in service provisions. We remedy this situation in this paper. We present a formal definition of services with context-dependent contracts. We define a composition theory of services with context-dependent contracts taking into consideration functional, nonfunctional, legal and contextual information. Finally, we present a formal verification approach that transforms the formal specification of service composition into extended timed automata that can be verified using the model checking tool UPPAAL. In [12] and [11], we introduced a formal framework, called FrSeC, that supports the specification, publication, discovery, selection, composition and verification of services with context-dependent contracts. The work reported in this paper is founded on this framework. We provide a formal specification of services with context-dependent contracts and their compositions. The composition theory of services takes into consideration the functional, nonfunctional, legal, and contextual aspects of services. We also present a formal verification approach that transforms the formal specification of service composition into UPPAAL [2] timed automata in order to verify service properties using model checking. Service-oriented Architecture (SOA) is an emerging view of the future of distributed computing and enterprise application development [4]. However, current approaches for the specification, publication, discovery, selection, and provision of services fall short in important respects. First, the relationship between the service contract and the conditions in which the service can guarantee its contract has been ignored, however these are necessary in order to associate the context of the service provider and the context of the service requester. Second, contextual information [3] is not well represented and not rigorously applied in service discovery and service provision. Third, current composition approaches compose only service functionality and ignore nonfunctional requirements. Thus, service contracts, and context information that are part of services are left out of the composition, and verification. Fourth and the last, the published approaches do not use formal methods for the specification of services, contracts, contextual representation and application, and service composition. Without a formal basis it is not possible to justify through formal verification the correctness conditions for service compositions and the satisfaction of contractual obligations in service provisions. The work reported in this paper eliminates these shortcomings. The basic building unit for SOA-based applications is service. It is normally understood that service is an autonomous and platform-independent software program, having its own distinct functionality and a set of capabilities related to this functionality. These capabilities are usually invoked by external consumer programs and are usually expressed via a published service contract. A service contract

A component-based development process for trustworthy systems

This paper introduces a new process for a rigorous component‐centered development of trustworthy systems. The rationale for our perspective of the process is two‐fold. The activities prescribed in a conventional software engineering development process are neither suitable nor sufficient for developing component‐based systems. Component‐based development methods that are currently practised do not support the explicit specification of trustworthiness properties, and are not based on rigorous principles. Hence they are not suitable for developing trustworthy systems. Trustworthiness is regarded as a composite nonfunctional property comprising the four attributes safety, security, availability, and reliability. They must be rigorously defined for components and systems composed from them. It is essential that the process enforces a direct evidence of trustworthiness in the systems that are developed following the process. Consequently, the development process, in addition to being reuse‐oriented, component‐oriented, and rigorous in all phases of the system lifecycle, should maintain the chain of evidence that the trustworthiness properties are preserved in every activity of every phase of system development. The proposed process includes several parallel interrelated tracks including component development, component assessment, component reuse, and component‐based system development and prescribes specific activities and tools for ensuring trustworthiness in all activities. Copyright

A user-centric semantic-based algorithm for ranking services: design and analysis

The number of online service providers and services hosted by them is rapidly increasing. Since services hosted by different service providers may have the same functionality, it is extremely hard for a user to determine those services that best match their requirements. To ease this difficulty, it is necessary that the service providing system rank those services based on users preferences, so that users receive only those services that suit them best. In this paper, a novel vector-based algorithm, which is multi-featured, semantic-based, and user-centric, is proposed for this service ranking problem. This algorithm overcomes all restrictions and limitations that exist in previously known vector-based ranking algorithms. The algorithm has been analyzed thoroughly with respect to performance, accuracy, and algorithmic complexity.

Adaptable Discovery and Ranking of Context-Dependent Services

This paper emphasizes the role of contextual information and legal rules in publishing services, formulating contracts, discovering services, and their impact on ranking and adaptability. We use Configured Service concept, which is a package that bundles together service functionality, service contract, and service provision context. Service providers only publish Configured Services in a service registry. Service requesters query the registry to discover available services that can match their requirements. Often there is a semantic gap between the service query and the services in the registry. To deal with this, we discuss three query types. The discovery processes, employing different matching processes that are appropriate for the query types, will rank the services in order to enable the requester choose the most relevant service(s). Ranking is also essential when the number of matchings is large. We identify the different situations that call for rediscovery and re-ranking of service queries. We include a brief account of formalism, within which all these activities are precisely described.