The paper proposes a comprehensive framework for representing and using non-functional requirements during the development process. The framework consists of five basic components which provide for the representation of non-functional requirements in terms of interrelated goals. Such goals can be refined through refinement methods and can be evaluated in order to determine the degree to which a set of non-functional requirements is supported by a particular design. Evidence for the power of the framework is provided through the study of accuracy and performance requirements for information systems. 1

This paper proposes a systematic treatment of NFRs in descriptions of patterns and when applying patterns during design. The approach organizes, analyzes and refines non-functional requirements, and provides guidance and reasoning support when applying patterns during the design of a software system. Three design patterns taken from the literature are used to illustrate this approach. 1. Introduction Requirements Engineering is now widely recognized as a crucial part of software engineering, and has established itself as a distinct research area. Equally important is how requirements drive the rest of software development. In particular, during the design phase, much of the quality aspects of a system are determined. Systems qualities are often expressed as non-functional requirements, also called quality attributes e.g. [1,2]. These are requirements such as reliability, usability, maintainability, cost, development time, and are crucial for system success

Quality characteristics are vital for the success of software systems. To remedy the problems inherent in ad hoc development, a framework has been developed to deal with non-functional requirements (quality requirements or NFRs). Taking the premise that the quality of a product depends on the quality of the process that leads from highlevel NFRs to the product, the framework's objectives are to represent NFR-specific requirements, consider design tradeoffs, relate design decisions to NFRs, justify the decisions, and assist defect detection. The purpose of this paper is to give an initial evaluation of the extent to which the framework's objectives are met. Three small portions of information systems were studied by the authors using the framework. The framework and empirical studies are evaluated herein, both from the viewpoint of domain experts who have reviewed the framework and studies, and ourselves as framework developers and users. The systems studied have a variety of characteri...

Non-functional requirements, such as modifiability, performance, reusability, comprehensibility and security, are often crucial to a software system. As such, these non-functional requirements (or NFRs) should be addressed as early as possible in a software lifecycle and properly reflected in a software architecture before committing to a detailed design. The purpose of this paper is to discuss how the treatment of NFRs as goals (which may be synergistic or conflicting) serves to systematically guide selection among architectural design alternatives. During the architectural design process, goals are decomposed, design alternatives are analysed with respect to their tradeoffs, design decisions are made rationalised, and goal achievement is evaluated. This process can be supported by by a body of organised knowledge. This paper outlines an approach by which such knowledge can be organized. This approach is illustrated by a preliminary study of architectural design for a KWIC (Key Word i...

Abstract—Nonfunctional Requirements (NFRs) have been frequently neglected or forgotten in software design. They have been presented as a second or even third class type of requirement, frequently hidden inside notes. We tackle this problem by treating NFRs as first class requirements. We present a process to elicit NFRs, analyze their interdependencies, and trace them to functional conceptual models. We focus our attention on conceptual models expressed using UML (Unified Modeling Language). Extensions to UML are proposed to allow NFRs to be expressed. We will show how to integrate NFRs into the Class, Sequence, and Collaboration Diagrams. We will also show how Use Cases and Scenarios can be adapted to deal with NFRs. This work was used in three case studies and their results suggest that by using our proposal we can improve the quality of the resulting conceptual models. Index Terms—Software design, requirements elicitation, nonfunctional requirements, goal graphs, UML conceptual models. 1

The dependability of technological systems is a growing social concern. Increasingly computer based systems are developed that carry the potential of increasing catastrophic consequences from single accidents. There have been significant research advances in assessment methods. However dependability assessment of computer systems in practice is still a very uncertain and often adhoc procedure. Decision making about system dependability is an uncertain affair and must account of failures in expertise and be capable of integrating different sources of evidence. A more meaningful way of reasoning about systems dependability can be achieved by rejecting current ad-hoc dependability assessment methods and replacing them with the idea of dependability argumentation. Bayesian Belief Networks (BBN’s) is proposed as the most promising technology to support this kind of dependability argumentation. 1

The conceptual modelling of business processes is becoming popular. The number of techniques and tools is growing fast. At the same time, an appropriate framework for understanding the quality of these modelling techniques is lacking. In this paper we report upon the development of a framework for understanding the quality of business process modelling techniques, called the Q-ME framework. The framework defines the elements that constitute a modelling technique and presents a number of quality properties as well as ways to operationalise them. In this paper, the framework is applied to illustrate the quality of the Dynamic Essential Modelling of Organisations (DEMO) business modelling technique. Conclusions are drawn both on the quality of DEMO and

Due to its economic impact "maintainability" is broadly accepted as an important quality attribute of software systems. But in contrast to attributes such as performance and correctness, there is no common understanding of what maintainability actually is, how it can be achieved, measured, or assessed. In fact, every software organization of significant size seems to have its own definition of maintainability. We address this problem by defining an unique two-dimensional quality model that associates maintenance activities with system properties including the capabilities of the organization. The separation of activities and properties facilitates the identification of sound quality criteria and allows to reason about their interdependencies. The resulting quality controlling process enforces these criteria through toolsupported measurements as well as manual inspections. We report on our experiences with the incremental development of the quality model and its application to large scale commercial software projects. Among the positive effects are a slowdown of decay and a significantly increased awareness for long-term quality aspects.

. Although quality issues such as accuracy, security, and performance are often crucial to the success of a software system, there has been no systematic way to achieve quality requirements during system development. We offer a framework and an implemented tool which treat quality requirements as goals to be achieved systematically during the system development process. We illustrate the process that a developer would go through, in building quality into a system. We have tested the framework on a number of studies involving a variety of quality requirements, organisational settings, and system types. Keywords: non-functional requirements, accuracy, security, performance, information systems, process, software quality, defect detection, conflicts. 1 Problem Software development is traditionally driven by functional requirements, i.e., the desired functionality of the system. For example, a credit card system should debit and credit accounts, check credit limits, charge interest, issue...

Maintainability is a key quality attribute of successful software systems. However, its management in practice is still problematic. Currently, there is no comprehensive basis for assessing and improving the maintainability of software systems. Quality models have been proposed to solve this problem. Nevertheless, existing approaches do not explicitly take into account the maintenance activities, that largely determine the software maintenance effort. This paper proposes a 2-dimensional model of maintainability that explicitly associates system properties with the activities carried out during maintenance. The separation of activities and properties facilitates the identification of sound quality criteria and allows to reason about their interdependencies. This transforms the quality model into a structured and comprehensive quality knowledge base that is usable in industrial project environments. For example, review guidelines can be generated from it. The model is based on an explicit quality metamodel that supports its systematic construction and fosters preciseness as well as completeness. An industrial case study demonstrates the applicability of the model for the evaluation of the maintainability of Matlab Simulink models that are frequently used in modelbased development of embedded systems.