by Fabrizio Fabbrini and Mario Fusani
The problem of defining a quality model to be used in the evaluation of software products is addressed. The model, based on the ISO/IEC 9126 standard, has been interpreted to meet the requirements of some classes of typical Health Care Information System applications, and exploits experience gained both in the field of medical informatics and in the assessment of software products. The values that result from weighing the quality characteristics according to their criticality evidence a quality profile which can be used both for evaluation and certification.
If the quality of a software product is to be evaluated, a quality model is needed, plus a method for evaluation and a quantitative scale of measures. A model is an abstract representation of an object: according to this very general definition, which implies the existence of several classes of models, we can define a quality model as a structured set of quality requirements.
Several high-level approaches to modelling the quality of software products have been proposed: these models are based on the idea that there are a number of important high-level quality factors of software products that should be measured. These factors are determined by lower-level criteria which are supposed to be much easier to measure than factors; for this reason, metrics are proposed as criteria. As a consequence, all the approaches proposed so far are based on the decomposition of a set of quality attributes in order to define a hierarchic structure of characteristics and a way to relate them to some technical aspects of the product. These and other efforts have led to the definition of a number of draft standards which directly address software measurement issues. The main and most popular one, ISO/IEC 9126, gives standard definitions of quality attributes and proposed measures, together with a set of application guidelines.
The ISO/IEC 9126 Quality Model
This model describes software quality as a function of six characteristics: Functionality, Reliability, Efficiency, Usability, Portability, Maintainability. This decomposition reflects the users' view and introduces the concept of quality in use: users are mainly interested in using the software product, and evaluate software mostly from the viewpoint of the performance and the service it provides, rather than on the basis of internal aspects or the development process. ISO/IEC 9126 suggests a further decomposition of each characteristic into a set of sub-characteristics: these sub-characteristics are a step closer to the quantitative, technical aspects of the software product. The proposed decomposition is presented in Figure 1.
Quality Profiles for Health Care Information Systems
Health Care Information Systems (HIS) have grown extensively in recent years, both with respect to the number of technologies involved and the functional target which they address, and can be included among critical computer systems from many perspectives (eg security, economy, safety).
Figure 1: Software Quality Model (ISO/IEC 9126).
Figure 2: Functionality Quality Profile.
Because of the intrinsic complexity of a modern HIS, it is not convenient to look for a global quality profile (a list of values obtained by assigning a score to each sub-characteristic) by applying the quality model to the whole software system. A broad classification of HIS software components into five categories (Networking, Archiving, Image Processing, Clinical, Administration), according to their functionality, allows us to obtain five separate quality profiles, easier to handle in the evaluation process. The quality profiles result from the application of the ISO/IEC 9126 model as a checklist to define the relevance of each sub-characteristic to each class. For each intersection (quality sub-characteristic, HIS software category) we suggest a value, representing in a five-level scale the relative importance of the sub-characteristic. As an example, Figure 2 shows the quality profile for the Functionality characteristic.
Fabrizio Fabbrini - IEI-CNR
Tel: +39 50 593 505
Mario Fusani - IEI-CNR
Tel: +39 50 593 512