A TOOL FOR WORKING WITH USABILITY GUIDELINES FOR E-COMMERCE WEB SITES Dragoş Cătălin Barbu, Costin Pribeanu National Institute for R&D in Informatics - ICI Bucureşti, Romania
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Abstract The interest for the quality and usability of e-commerce web sites significantly increased in the last years, as a result of the proliferation of web applications. The large number of guidelines and the variety of existing collections requires appropriate instruments for collecting and consulting a guideline data base. In this paper we describe a tool for working with usability guidelines. This tool is implementing a hierarchical structure of guidelines that are satisfying both domainspecific criteria and ergonomic criteria. Keywords Usability, guideline-based evaluation, usability guidelines, software tools, tools for working with guidelines. 1. Introduction The interest for the quality and usability of web sites increased significantly in the context of Internet based economic activities, whose profitability is depending more and more on both the utility and usability of the application. Usable systems with a poor functionality create the feeling to the user that the user interface (UI) is leaving out of his reach many capabilities. On the other hand, many systems which provide with a reach but unstructured set of functions are perceived as being built regardless of the context of use. Although the concern for respecting usability guidelines is increasing, the usability of many e-commerce web sites is still low. An explanation is the huge number of existing guidelines and the fact that guideline-based evaluation requires appropriate tools for working with guidelines. In this paper we present a theoretical framework and a tool for working with usability guidelines for e-commerce web sites. The rest of this paper is structured as follows. In the next section we will describe some related work in the area of usability prescriptions and our approach in structuring a collection of usability 169
guidelines. Then we will present the tool for working with guidelines. The paper ends with conclusion and future work. 2. Usability prescriptions Usability standards In the former version of ISO 9126:1991 standard, usability was defined as a software quality attribute that bears on the capability of being easy to comprehend, understand, and operate. Another definition could be found in the draft ISO standard 9241-11:1994 in which usabiliy was defined from a broader perspective as the extent to which a product can be used by specified users to achieve specified goals effectively, efficiently and with satisfaction in a specified context of use. The context of use has four main components: user, tasks, platform and environment. These definitions were revised and integrated in the new version of ISO 9126 standard on quality of software systems as follows: • Usability is the capability of a software system to be understood, learned, used, and liked by the user when used under specified conditions. (ISO/IEC 9126-1:2001) • Quality of use is the extent to which specified users accomplish specified goals with effectiveness, productivity, security and satisfaction in a given context of use. (ISO/IEC TR 9126-4:2004) The quality of use is closely related with four quality characteristics: functionality, usability, reliability and efficiency. As such, it is more comprehensive and requires a broader view on design and evaluation of interactive systems targeting a specified context of use. Usability factors and principles In the related literature there are many approaches regarding the key factors and design principles that could be used by designers in order to develop usable systems. Nielsen proposed the heuristic evaluation method which is using ten widely recognized principles (heuristics): visibility of system status, compatibility with the activity, user freedom and control, consistency, error prevention, recognition instead of recall, flexibility, aesthetics and minimalist design, quality of error messages [8]. Bastien and Scapin [2] defined 18 ergonomic criteria for the evaluation of a user interface. Ergonomic criteria are used for several purposes: describing the rationale for using guidelines, evaluating the ergonomic quality of user interfaces, indexing, and accessing guideline databases. Dix et al [3] proposed a organization of design principles in three categories, based 170
on their effects: (a) easy to learn (b) flexibility and (c) robustness. Welie et al. [9], proposed a layered model of usability which includes usage indicators (measuring effectiveness, efficiency and satisfaction, e.g. learnability improving efficiency), means (affecting usage indicators, e.g. consistency improves learnability) and knowledge (expressing how to use means). In their model, the usability guidelines are embodying knowledge on how the design of a user interface is affecting the usage indicators. Other layered models were proposed by Seffah, Kecci and Donyaee [8] (four layers: factors, criterions, metrics and data) and Abran et al [1] (5 components: efficacy, efficiency, satisfaction, ease to learn and security). Structuring the guideline base Heuristics are general principles expressed in a straightforward way as an imperative prescription. Guidelines are providing with more detailed prescriptions, following a guideline template which includes among others: a statement, a list of bibliographic references, a rationale justifying the guideline, positive and negative examples, evaluation criteria. Usually, guidelines are organized in guideline bases and sections according to various evaluation criteria. Accessing guidelines for a target interface could be done either by following guidelines organization or by using key words. A problem with existing collections is that they are heterogeneous as regarding the structure and the number of attributes. In a previous paper [7] we propsed a layered structure based on both application domain and ergonomic criteria. According to the application domain, specific guidelines are needed that are related to marketing, commercial, social, or educational aspects. This model is illustrated in Figure 1.
Figure 1 The structuring model Heuristics are specific to the domain and are used to organize the usability 171
guidelines within a guideline base. General UI guidelines are respecting ergonomic criteria. In this respect, the ergonomic criteria are used for the indexing of guidelines guidelines. 3. A tool for working with guidelines Requirements and solution We consider that the most efficient structure should follow the criterion-heuristicguideline relationship. For an e-commerce web-site design, high level heuristics are addressing the core issues relate to shopping on the web: product information, product navigation, purchasing transaction and user support. Heuristics could also take a general guideline description model, including statement, examples, and references. This way moving from heuristics to guidelines along the hierarchy is a seamless transition. The tool for working with guidelines is intended to support the following activities: • Prescription administration: collecting, editing, organizing, prescriptions and associated objects. • Prescriptions consulting by designers and evaluators during the development process. The tool was developed for a Desktop PC platform under Windows XP operating system. We took into account the possibility of extension of the tool for web accessibility. The software solution adopted for this project is one oftenly used in practice: the combination Apache / MySQL / PHP: • PHP is the programming language (scripting) • MySQL is Data base management system - DBMS ( database server ) • Apache is the Web server (server HTTP ) The user interface This tool can be accessed through a web user interface which includes two categories of dialog units, corresponding to the user’s role: (a) database consulting and (b) database administration. Data base administration means editing of heuristics, guidelines, criteria, references as well as organization of heursitics and guidelines within hierarchical layers. The access to the administrative functions is based on authentication with username and password. Firstly, the user selects the category of entities to visualize (e.g. heuristics, guidelines, criteria etc.) Then s(he) selects the entity and the operation to perform onto it (adding, changing, deleting), as illustrated in Figure 2 where a usability guideline is currently selected for editing. 172
Figure 2 Dialog unit for editing a usability guideline The “general guideline” attribute enables a hierarchical organization of guidelines on seveal layers. By using two buttons, the user can manipulate the association between a heurstic or a guideline with a criterion, an example or a reference (add or delete an association). Other guideline attributes are: title, statement, justification and comments. 4. Conclusion Technology is no longer seen as the driving force in the development process. Rather, technology is a means to meet customer needs. The quality of e-commerce web sites is a trade-off between utility and usability. Utility is related to the appropriateness of computer tools for a given domain / problem. Usability guidelines that are covering almost all known usability problems could heavily improve the quality of a user interface. Guideline-based evaluation requires tools for working with guidelines. In this paper we proposed a tool for working with usability guidelines. The tool is implementing a layered structure of prescriptions which has several benefits: • It integrates three types of prescriptions widely used in design and evaluation: criteria, heuristics and guidelines. • It provides designers and evaluators with relevant heuristics and guidelines 173
for a given application domain. Domain experts could be more effectively involved in the design and evaluation of interactive systems. Although this tool is primarily intended for the computed-aided evaluation it is also useful for designers, in order to prevent usability problems. In future, we intend to use this tool in order to create a guideline base for the usability evaluation of augmented reality applications. •
Acknowledgement This work is supported from the research project PN 0503/2009. References 1. Abran, A., Khelifi, A., Surym, W. & Seffah, A. (2003). “Usability Meanings and Interpretations in ISO Standards”. Journal of Software Quality, Vol.11, No.4, 2003. pp. 325-338. 2. Bastien, J.M.C. & Scapin, D.L. (1993) Evaluating a User Interface with Ergonomic Criteria INRIA Report, Roquencourt. 3. Dix, A., J.Finlay, G.Abowd & R.Beale (1993) Human-Computer Interaction, Prentice Hall. 4. ISO/DIS 9241-11:1994 Information Technology – Ergonomic requirements for office work with visual display terminal (VDT) - Guidance on usability. 5. ISO DIS 9126-2001 Software Engineering - Software product quality. 6. Nielsen, J. (1994). “Heuristic evaluation”. In Nielsen, J., and Mack, R.L. (Eds.), Usability Inspection Methods, John Wiley & Sons, New York, NY. 7. Pribeanu, C. (2005) “A domain-oriented approach in structuring user interface guidelines”. Proceedings of UIQM Workshop, INTERACT 2005, Rome 12-13 September 2005. pp. 90-93. 8. Seffah, A., Kecci, N., Donyaee, M. (2001) “QUIM – A Framework for Quantifying Usability Metrics in Software Quality Models”. Proceedings of APAQS’01. Hong Kong. pp. 311-318 9. Welie, M. van, Veer, G.C. van der & Eliëns, A. (1998) “Breaking down Usability”. Proceedings of Interact’99, Edinbourgh, UK.
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