An Investigation of the Weaknesses of the ISO 9126 International ...

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Figure 1. ISO 9126 quality model for external and internal quality (characteristics and sub-characteristics). Figure 2. ISO 9126 quality model for quality in-use (characteristics). The second [3], third [4] and fourth [5] parts of the ISO 9126 series provide the following information: • Sets of metrics for each external quality subcharacteristic, internal quality sub-characteristic and quality in-use characteristic. • Explanations of how to apply and use these sets of metrics. • Examples of how and where to apply these metrics during the software product lifecycle. III. THE QUALITY MEASUREMENT DIVISION OF ISO 25000: AN OVERVIEW One of the objectives of this new ISO 25000 series (and what makes it different from the current ISO 9126 series) is the harmonization of its contents with the software measurement terminology of ISO 15939 [10] which itself based on the ISO metrology terminology [21]. Figure 3 shows the structure of the quality measurement division (ISO 2502n) series that is to replace the current four-part ISO 9126 series of standards [22]. This proposed quality measurement division (ISO 2502n) will consist of five documents: • ISO 25020 on Measurement Reference Model and Guide. • ISO 25021 on Quality Measure Elements. • ISO 25022 on Measurement of Internal Quality. • ISO 25023 on Measurement of External Quality. • ISO 25024 on Measurement of Quality in Use. The work on ISO 25000 is being carried out by Working Group 6 (WG6) of the software and system engineering subcommittee (SC7) of the ISO/IEC joint technical committee (JTC1) on Information Technology, that is, ISO/IEC JTC1/SC7 1 . 1 The author is a Canadian representative and committee member of the ISO/IEC Joint Committee 1 – Subcommittee 7 (JTC1/SC7) – Work Group 6 on Software Evaluation and Measurement. 276
Figure 3. The structure of the measurement division (ISO 2502n series). IV. THE WEAKNESSES OF ISO 9126 In this section we will discuss the weaknesses of the ISO 9126. However, these weaknesses will be classified into two classes, that is, the weaknesses which we have identified during our previous work, and the weaknesses which are discovered by other researchers and practitioners. A. Self-Discovered Weaknesses During our previous research, we have found the following weaknesses of ISO 9126: 1) The terminology needs to be harmonized with the ISO International Vocabulary of Basic and General Terms in Metrology [8]. 2) The metrics in ISO 9126 parts 2, 3, and 4 are completely merged and need to be classified into base and derived metrics to be aligned with the ISO 15939 [9]. 3) It is to be noted that the ranges of the results of many of the metrics in ISO 9126 are between 0 and 1. Therefore, it is easy to convert them to percentage values. However, from our point of view, these results would be easier to understand if they were ranked in terms of qualitative values; for example, for task completion, if the percentage result is 100%, then the completion of the task is labeled “excellent”; if the result is 80%, then the completion of the task is labeled “very good”; and so on [10, 13]. 4) When mapping the ISO 9126 to ISO 12207, many of the ISO 9126 quality metrics referred to ISO 12207 processes. However, as known, each process in ISO 12207 contains a number of different activities. Thus, it is more usable for the ISO 9126 users to refer to the activities of the ISO 12207 [11, 12]. B. The Weaknesses Discovered by other Researchers The following are the weaknesses which have been identified by other researchers: 1) Jung et al. [14] stated that including the six compliance sub-characteristics leads to two possible results. The first possibility is that the compliance sub-characteristic for each characteristic belongs to its characteristic as defined in ISO 9126. The second possibility is that the six compliance subcharacteristics constitute a separate dimension [14]. Furthermore, their results reveal ambiguities in the way that ISO 9126 is structured in terms of characteristics and sub-characteristics. 2) Chua and Dyson [15] - in their investigation - uncovered some inherent weaknesses in the ISO 9126 quality model, particularly with regards to the Usability characteristic. To make the model simpler to use for educators, who may not be usability experts, they propose that this characteristic should be extended to include more specific factors such as consistency, simplicity, legibility and color use. It is also suggested that a Help sub-characteristic be included as part of Usability, mainly to ensure that this important factor should not be neglected. In addition, we propose the inclusion of user satisfaction as a global characteristic to summarize the general impact of the system on the user in their specific educational context and given their specific requirements. With these improvements, ISO 9126 could be a useful model for evaluating the quality of e-learning systems [14]. 3) Based on the ISO 9126 standard, as well as an investigation of other models proposed by various Quality Measure Elements (ISO 25021) Measurement of External Quality (ISO 25023) Measurement of Internal Quality (ISO 25022) Measurement of Quality in Use (ISO 25024) easurement Reference Model and Guide (ISO 25020) authors, Abran et al. [16] stated that revised structure for a usability model need to be proposed, including the addition of two characteristics to the ISO 9126 standard which had been selected as their baseline: learnability and security. Then, specific metrics for 277
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