Workflow management systems (WfMSs) have been used to support various types of business processes for more than a decade now. In workflows for e-commerce and Web-services applications, suppliers and customers define a binding agreement or contract between the two parties, specifying Quality of Service (QoS) items such as products or services to be delivered, deadlines, quality of products, and cost of services. The management of QoS metrics directly impacts the success of organizations participating in e-commerce. Therefore, when services or products are created or managed using workflows, the underlying workflow system must accept the specifications and be able to estimate, monitor, and control the QoS rendered to customers. In this paper, we present a predictive QoS model that makes it possible to compute the quality of service for workflows automatically based on atomic task QoS attributes. To this end, we present a model that specifies QoS and describe an algorithm and a simulation system in order to compute, analyze and monitor workflow QoS metrics. 1

We present a foundational theory of software system reliability based on components. The theory describes how component developers can design and test their components to produce measurements that are later used by system designers to calculate composite system reliability --- without implementation and test of the system being designed. The theory describes how to make component measurements that are independent of operational profiles, and how to incorporate the overall system-level operational profile into the system reliability calculations. In principle, the theory resolves the central problem of assessing a component, which is: a component developer cannot know how the component will be used and so cannot certify it for an arbitrary use; but if the component buyer must certify each component before using it, component-based development loses much of its appeal. This dilemma is resolved if the component developer does the certification and provides the results in such a way that the component buyer can factor in the usage information later, without repeating the certification. Our theory addresses the basic technical problems inherent in certifying components to be released for later use in an arbitrary system.

Software components are today the most promising approach to dealing with the complexity and uneven quality of software systems. The design-using-components paradigm has been extremely successful in almost every engineering field, with its benefits of rapid, routine, reliable system construction. The central dilemma of software design using components is that component developers cannot know how their components will be used and so cannot describe component properties for an unknown, arbitrary situation; but if the component customer (system designer) must determine relevant properties of each component before using it, component-based development loses much of its appeal. In technical terms, component behavior depends on the operational profile the component sees when in place in a larger system; in turn, that profile depends both on system usage and the internal structure of the system, neither of which can be known to the component developer.

Progress is being made toward being able to calculate software system reliability from the reliability of the components and information about the structure of their interactions. This paper enumerates the outstanding problems and provides solutions, or pointers to solutions, for each. 1 Introduction Software system reliability estimates are typically based upon data collected while testing the system as a whole [6]. However, there is growing interest in estimating system reliability from the reliabilities of its constituent components. This technique is both pragmatically appealing, and supportive of the treatment of software development as an engineering discipline. Pragmatically, the technique has potential for increasing the cost-effectiveness of reliability estimation and encouraging code reuse by creating a market for components with certified reliabilities. It also supports the transformation of software engineering into a discipline more like that of "traditional " engineeri...

In engineering design, the idea of aggregating standardized components to create a complex system has allowed engineers to create better systems more easily. Components are described in a handbook, where each has a “data sheet ” entry. Its data sheet describes what a component does, and equally important, it gives constraints that allow the system designer to decide if the component is “good enough ” for the application. For mechanical components, these constraints concern, for example, the life expectancy of the component. The success of the component-construction paradigm in mechanical and electrical engineering has led to calls for its adoption in software design. Software is embedded in systems with mechanical and electrical components, systems designed using component techniques from these other branches of engineering. The system designer of an embedded system

Composition of software elements into assemblies (systems) is a fundamental aspect of software development. It is an important strength of formal mathematical specification that the descriptions of elements can be precisely composed into the descriptions of assemblies. Testing, on the other hand, is usually thought to be “non-compositional. ” Testing provides information about any executable software element, but testing descriptions have not been combined to describe assemblies of elements. The underlying reason for the compositional deficiency of testing is that tests are samples. When two elements are composed, the input samples (test points) for the first lead to an output sample, but it does not match the input test points of the second, following element. The current interest in software components and component-based software development (CBSD) provides an ideal context for investigating elements and assemblies. In CBSD, the elements (components) are analyzed without knowledge of the system(s) to be later assembled. A fundamental testing theory of component composition must use measured component properties (test results) to predict system properties. This paper proposes a testing-based theory of software component composition based on subdomains. It shows how to combine subdomain tests of components into testing predictions for arbitrarily complex assemblies formed by sequence, conditional, and iteration constructions. The basic construction of the theory applies to functional behavior, but the theory can also predict system non-functional properties from component subdomain tests. Compared to the alternative of actually building and testing a system, the theoretical predictions are computationally more efficient. The theory can also be described as an exercise in modeling. Components are replaced by abstractions derived from testing them, and these models are manipulated to model system behavior.

Most software-component research has been directed at functional specification of software components. The other, equally important, side of the coin is component quality. We present a foundational theory of reliability based on components. The theory describes in principle how component developers can make measurements that are later used by system designers to calculate --- without implementation and test --- system reliability. The theory is a "microscopic" one that describes in detail how component properties are reflected in systems designed using those components.