Formalization of Component Substitutability

AbstractComponent-Based Software Engineering (CBSE) is increasingly used to develop large scale software. In this context, a complex software is composed of many software components which are developed independently and which are considered as black boxes. Furthermore, they are assembled and often dependent from each other. In this setting, component upgrading is a key issue, since it enables software components to evolve. To support component upgrading, we have to deal with component dependencies which need to be expressed precisely. In this paper, we consider that component upgrade requires managing substitutability between the new and the old components. The substitutability check is based on dependency and context descriptions. It involves maintaining the availability of previously used services, while making sure that the effect of the new provided services do not disrupt the system and the context invariants are still preserved. We present here a formal definition and a verification algorithm for safe component substitutability

An algebra for feature-oriented software development

Feature-Oriented Software Development (FOSD) provides a multitude of formalisms, methods, languages, and tools for building variable, customizable, and extensible software. Along different lines of research different ideas of what a feature is have been developed. Although the existing approaches have similar goals, their representations and formalizations have not been integrated so far into a common framework. We present a feature algebra as a foundation of FOSD. The algebra captures the key ideas and provides a common ground for current and future research in this field, in which also alternative options can be explored

Type System for the ComponentJ Programming Language

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Informática.With the constant evolution of software systems need arises for more structured implementations, where processes like software updates and changes in systems can be easily made, with no need to change what had previously been implemented. One possible solution to this problem is the use of component-based programming languages. This kind of programming languages tries to promote not only code reuse but also a black-box discipline where it is not needed how a service is implemented, but only its interface so that it can be used. The ComponentJ programming language seeks to provide a simple way to perform component creation and composition, making this new programming paradigm somewhat easy to use. Because ComponentJ is meant to be an extension to the Java programming language it becomes possible to implement components using the whole expressiveness of this language. It is also possible, in ComponentJ, to dynamically change components and the object structure based on runtime decisions. This dynamic reconfiguration process allows, for instance, to perform changes/updates to a certain software system without having to stop its execution. The goal for this project is to implement a type system for the ComponentJ programming language, based on the work presented in [32, 28]. Type verification is syntax driven, and uses structural equivalence of types. Advanced techniques such as subtyping and type inference are also included in order to make the language more flexible. Besides the static type checker, a dynamic checker is also included, allowing the type safe application of runtime changes to the system (dynamic reconfiguration of objects) before their application

Checking compatibility and substitutability of software components

In component-based systems, two components are compatible if all possible sequences of services requested by one component can be provided by the other component. It has been recently shown that for verification of compatibility, the behavior of interacting components, at their interfaces, can be modeled by labeled Petri nets with labels representing the requested and provided services. Such component models are then composed and the composition operation is designed in such a way that component incompatibilities are manifested as deadlocks in the composed model. Compatibility verification is thus performed through deadlock analysis of the composed models. Component compatibility is also used for the verification of component substitutability; if the new component is compatible with all components that interact with the old component, it can safely replace the old one

Incremental Composition of Software Components

In component-based systems, two interacting components are compatible if all sequences of services requested by one components can be provided by the other component. In the case of several components interacting with a single provider, as is typically the case in client–server computing, the requests from different components can be interleaved and therefore verifying component compatibility must check all possible interleavings of requests from all interacting components. Incremental composition of interacting components eliminates this need for exhaustive combinatorial checking of the interleavings by imposing some restrictions on the interleavings. The paper introduces simple conditions which must be satisfied by the interacting components for their composition to be incremental and illustrates the concepts using simple examples of interactions

Evolving Software with Extensible Modules

We present the design of the programming language Keris, an extension of Java with explicit support for software evolution. Keris introduces extensible modules as the basic building blocks for software. Modules are composed hierarchically revealing explicitly the architecture of systems. A distinct feature of the module design is that modules do not get linked manually. Instead, the wiring of modules gets infered. The module assembly and refinement mechanism of Keris is not restricted to the unanticipated extensibility of atomic modules. It also allows to extend fully linked systems by replacing selected submodules with compatible versions without needing to re-link the full system. Extensibility is type-safe and non-invasive; i.e. the extension of a module preserves the original version and does not require access to source code

Type-Safe Prototype-Based Component Evolution

Component-based programming is currently carried out using mainstream object-oriented languages. These languages have to be used in a highly disciplined way to guarantee flexible component composition and extensibility. This paper investigates abstractions for component-oriented programming on the programming language level. We propose a simple prototype-based model for first-class components on top of a class-based object-oriented language. The model is formalized as an extension of Featherweight Java. Our calculus includes a minimal set of primitives to dynamically build, extend, and compose software components, while supporting features like explicit context dependencies, late composition, unanticipated component extensibility, and strong encapsulation. We present a type system for our calculus that ensures type-safe component definition, composition, and evolution

A Behavioral Model of Component Frameworks

When using a component framework developers need to respect the behavior implemented by the components. Static information about the component interface is not sufficient. Dynamic information such as the description of valid sequences of operations is required. Instead of being in some external documentation, this information should be formally represented and embedded within the components themselves, so that it can be used by automatic tools. We propose a mathematical model and a formal language to describe the knowledge about behavior. We rely on a hierarchical model of deterministic finite state-machines. The communication between the machines follows the Synchronous Paradigm. We favor a structural approach allowing incremental simulation, automatic verification, code generation, and run-time checks. Associated tools may ensure correct and safe reuse of the components. We focus on extension of components through inheritance (in the sense of sub-typing), owing to the notion of behavioral refinement

A theory and model for the evolution of software services

Software services are subject to constant change and variation. To control service development, a service developer needs to know why a change was made, what are its implications and whether the change is complete. Typically, service clients do not perceive the upgraded service immediately. As a consequence, service-based applications may fail on the service client side due to changes carried out during a provider service upgrade. In order to manage changes in a meaningful and effective manner service clients must therefore be considered when service changes are introduced at the service provider's side. Otherwise such changes will most certainly result in severe application disruption. Eliminating spurious results and inconsistencies that may occur due to uncontrolled changes is therefore a necessary condition for the ability of services to evolve gracefully, ensure service stability, and handle variability in their behavior. Towards this goal, this work presents a model and a theoretical framework for the compatible evolution of services based on well-founded theories and techniques from a number of disparate fields.