Aleksandar Dimov

Modeling Uncertainties in the Estimation of Software Reliability A Pragmatic Approach

The increasing usage of computer based systems for safety critical operations in applications such as nuclear, space, and automotive systems demands a systematic way of estimating software reliability. The high reliability requirements of safety critical software systems make this task imperative as well. Due to the specifics of software systems and the lack of any universally accepted models it is very difficult to predict the true reliability value of the system. Unfortunately none of the existing software reliability models neither acknowledge nor address this fact. There exist multiple uncertainty factors that influence reliability estimation of safety critical software systems. In this paper, we first define the scope of the important factors in the reliability models and describe a new approach to obtain a realistic estimate for system reliability. For this purpose, we consider different kinds of reliability models also taking into account the system architecture. The influence of uncertainty factors in the models is analyzed to obtain uncertainty bounds. They show an interval, where the true reliability should lie within it. This way system architects may use a so-called worst-case reliability estimation, given by the lower interval bound, for system analysis. We also demonstrate our proposed approach with real data taken from safety-critical applications.

Fuzzy Reliability Model for Component-Based Software Systems

Component-based software engineering has been projected off-late as an appropriate paradigm for embedded systems development. However this becomes feasible only if the dependability attributes, such as reliability, of embedded systems can be properly estimated and guaranteed using appropriate models. Another recent trend is the prevalence of architectural modelling of software systems due to the advantages such as composability reasoning and analysis of system behaviour as well as the flexibility and reusability of models. However, a major issue is that there exist uncertainty in the reliability parameters associated with the traditional testing-based approaches for particular architectural entities (e.g. components and/or connectors). In this context, we propose a new approach for the reliability estimation of component-based software systems, which steps on an architectural model of the system using Generalized Nets. This notation is a generalization of Petri nets and is an all-purpose formal modelling technique for the description of parallel phenomena. For the reliability description, we apply possibility theory, which has the potential to solve the uncertainty aspect. This is based on fuzzy sets and describes reliability properties of software components in systems architecture with fuzzy measures.

How do we collect data for software reliability estimation

Together with the increasing influence of software systems in all aspects of everyday life there is also a need to focus on their non-functional characteristics. Reliability is one important software quality characteristic, which is defined as the continuity of correct service. Reasoning and modelling are necessary in order to achieve desired levels of reliability both during design and usage of software systems. The usefulness of reliability models are dependent on the input data we provide to these models, which influences the accuracy of the estimations we perform. There exist different techniques for gathering data for software reliability estimation and the aim of this paper is to make a good overview of them. As software testing is the most widely applied and researched technique among them, we also briefly present the current state of the art in application of different testing methods for the collection of data to be used for reliability estimation.

Experience-based approach for adoption of agile practices in software development projects

The agile approach for software development has attracted a great deal of interest in both academic and industry communities in the last decade. Nevertheless the wide adoption of agile methods in ever growing number of software development projects, shifting the development process of an organization to an agile one is not straightforward. Certain considerations for the applicability of agile practices should be taken into account when this transition is performed. In this paper, an approach for situational engineering of agile methods is proposed. The approach is based on the experience gained in adopting agile practices in both internal and external projects of organizations. A knowledge-base supporting the selection of agile practices that are suitable for certain project is introduced. Automated generation of appropriate software development process is included as well. Particular realization of the approach supported by SPEM-based tools is also presented in the paper.

Reliability models in architecture description languages

In recent years, component-based approach has shown a great potential in cost and time reduction of software development. Research in non-functional characteristics also becomes a major issue in this domain. For these reasons, special interest raises the ability for compositional reasoning, in a formal way, about non-functional characteristics. In this paper, we focus the attention on one of them, namely reliability. Although, in the last 20 years, there appeared a number of Component-Based Reliability Models (CBRMs), there does not exist enough efforts to relate CBRM to methods for description of software architecture. Instead, a separate research direction in Architecture Description Languages (ADLs) evolved independently. The paper shows a way to bridge the gap between ADLs and CBRMs and lay out possibilities for comparison of different CBRMs. An extension of Petri-nets and Finite-State Machines, called Generalized Nets, is used to specify software architecture.

On the estimation of software reliability of component-based dependable distributed systems

Component based development, which had been successful in enterprise computing, shows promises to be a good development model for automotive systems. This is possible if several dependability concerns of the embedded systems can be properly addressed by the models, frameworks and integration platforms. SaveCCM is a component model for automotive systems developed by employing component based system design. Our ongoing research is related to estimation of software reliability for this model. In this paper, we provide a survey of the state of the art on research techniques for the estimation of system reliability based on component reliabilities and architectures. We further discuss their pros and cons with reference to our architectural model and discuss some practical considerations. Based on this we also present the basics of our approach to reliability modeling of SaveCCM architectures.

Software reliability assessment via fuzzy logic model

Recently in software engineering it became of great importance to be able to reason about non functional characteristics of software. This holds for a large variety of application areas like embedded and safety-critical software systems as well as service-oriented systems. Currently there exist a number of models for evaluation of software reliability, which are based on statistics and probability theory. However, the assumptions of existing models introduce imprecision in the reliability estimations. In this paper we are making a step towards solving of this problem by introducing a fuzzy logic approach for estimation of software reliability. Our approach is further validated with a case-study.

System level modeling of component based software systems

One of the main problems in the area of Component-Based Software Engineering (CBSE) is how to facilitate the integration of software components into large-scale and complex systems. A possible solution is to enforce on software architecture of the system. The increased importance of architecture in CBSE raises the necessity to explore and develop methods for its formal description. Several languages and notations, named architecture description languages (ADL), were developed for formal system level specification. This paper overviews them and outlines the main directions for their evolution.

User-oriented service composition platform

Currently teachers and students encounter some difficulties in the identification of tools that best fit their needs on the one hand and the composition of these tools into more complex educational processes on the other hand. The so-called service composition platforms offer a promising possibility to overcome this problem. Although numerous service composition platforms already exist, they are still not completely appropriate for application in the learning domain. In this paper we define the requirements for a service composition platform that could be used in learning, and make the first steps for its development - architecture and UI design.

Software availability in the cloud

Cloud computing is becoming very prevalent in many application areas. However there is still little research in application of software engineering techniques for development of software systems, intended for execution in cloud environments. In this paper we make a deeper look at currently existing architectural tactics for achieving availability in the cloud. A case study at the end of the paper shows that using some of these tactics one may achieve high levels of availability.