Conceptual Model

Various methods for evaluating software architectures have been defined to support holis- tic reasoning and decision making. We adhere to the holistic ethos in defining our frame- work for evaluating architectural stability. Our framework extends the “ISO/IEC 42030, Systems and Software Engineering —Architecture Evaluation” [507] [506]. More specif- ically, we follow the overall conceptual framework of the ISO/IEC standards for general architectural evaluation [507] [506] to generate a standards-conforming framework for sta- bility evaluation. Following such standards allows having a near-to-completeness system- atic approach for stability evaluation. We borrow the basic concepts from the ISO/IEC standards to be employed with the focus on architectural stability.

Figure 8.1 traces the progress of architectural stability evaluation through the concep- tual framework. Following the ISO/IEC standards [507] [506], which considers stakehold- ers’ concerns as a base of the evaluation, we adopt the concept of concerns to represent the assurances about the behaviour of the architecture that stakeholders expect to obtain. These concerns are framed into stability evaluation objectives, that drive the evaluation approach. Stability evaluation objectives are traced down to stability attributes analysis and assessment objectives, in order to express them in terms of attributes of interest. Stability attributes of interest cover the attributes that the architecture’s behaviour is expected to exhibit while operating in its environment. The results of the attributes analysis and assessment are used to inform the stability evaluation approach, in order to determine whether stability concerns of the stakeholders are satisfied, for decision making and reporting purposes.

Figure 8.1: Progress of Stability Evaluation

The overall conceptual model is depicted in Figure 8.21. Table 8.1 illustrates the mapping between the ISO/IEC standards for general architectural evaluation and the Stability Evaluation Framework2_{. The Stability Evaluation Framework aggregates three}

main components: (i) context of evaluation, (ii) stability evaluation approaches and their assessment criteria, and (iii) stability attributes analysis methods and their analysis cri- teria. Details of these components are presented in the next sections respectively.

1_{Figures use the conventions for class diagrams defined in ISO/IEC 19501 [508]. We use coloured fill} shapes to indicate entities that are outside the boundaries of the model depicted in the figure.

Table 8.1: Mapping of the ISO/IEC Standards for General Architectural Evaluation and the Stability Evaluation Framework

Concept Architecture Evaluation Stability Evaluation

Evaluation the degree to which the architecture meets end-user

needs, expectations or requirements

the degree to which the architecture is able to maintain the expected behaviour stable

Stakeholders individual, team, organisation, or classes thereof,

having an interest in a system

the entities that have interest in the architecture’s behaviour and related concerns

Concerns interest in a system relevant to one or more of its

stakeholders

represent the assurances about the behaviour of the architecture that stakeholders expect to obtain Evaluation Objective manifests one or more stakeholder concerns define how stability concerns will be addressed Evaluation Approach defines value assessment objectives deriving them

from the evaluation objectives, and specify value assessment methods and related information sources to address evaluation objectives

describes how stability information will be gathered and processed

Factor represents one or more stakeholder concerns,

traceable to one or more architecture evaluation objectives, is used by a set of value assessment objectives to drive the value assessment

expresses a stability concern or stability advantage associated with the architecture

Evaluation Plan includes the architecture evaluation objectives, and their relative importance, and the evaluation scope

guides the derivation of stability evaluation

Evaluation Report documents the scope and objectives for the

architecture evaluation, stakeholders’ concerns addressed by the architecture evaluation, and the derivation of the final conclusions from the value assessment results

documents the scope and objectives for stability evaluation, stakeholders’ stability concerns, and the overall conclusions of the stability evaluation

Information sources useful for creating an understanding of the architecture as a basis for making judgements and drawing conclusions for an architecture evaluation

useful for creating an understanding of the architecture’s behaviour

Assessment Method describes how information will be gathered and

processed, and how value assessment criteria will be applied to the processed information to yield value assessment results

describes how behavioural stability information will be gathered and processed, and how stability assessment criteria will be applied on the processed information to yield stability assessment results

Attribute some characteristic or property of the architecture a behavioural property of the architecture’s

intended behaviour that needs to be considered for stability

Table 8.1 (cont.)

Concept Architecture Evaluation Stability Evaluation

Attribute Analysis Objectives express the value assessment objectives in terms of conditions on attributes of interest

are down-traces of Stability Evaluation Objectives to express them in terms of attributes of interest Attribute Analysis Criteria are conditions that must be met by or the tests

that must be passed by the measured values of the attributes of interest

are stability conditions that must be met or the tests that must be passed by the system Attribute Analysis Method describes the method for analysing one or more

attributes of interest to address the attribute analysis objectives

describes the method for analysing one or more stability attributes to address the Stability Attribute Analysis Objectives

Attribute Analysis Results are used as evidence in a value assessment method to make decisions or draw conclusions as to how well the architecture and/or the system

characterised by the architecture addresses concerns

are the outcomes of attribute analysis methods, used as evidence on how well the architecture’s behaviour addresses the concerns for stability