Discovering Requirements with Scenarios: The ART-SCENE Solution
by Neil Maiden
Discovering requirements such as what people want from new computer systems remains a challenging problem for most European organisations. ART-SCENE is an innovative new solution to this problem. We already know that scenarios stories that describe how the future system might work help us to discover these requirements. ART-SCENE takes this a stage further by enabling organisations to generate scenarios automatically and use them systematically in discovering people's requirements for new systems.
Although scenarios are commonplace in systems development, developers rarely know how many scenarios to produce, what their content and structure should be, and how they should use them to discover new requirements from users. As a result, most software developers use scenarios in an ad hoc, non-optimal way. What they need are tools that are clear and simple to use, which allow them to generate and use scenarios more systematically, and hence effectively.
ART-SCENE is one solution to these problems. It is a process with Web-enabled tool support that organisations can use to generate and walk through scenarios, and thus discover the complete and correct requirements for new computer systems. It enhances current Rational Unified Processes and Use Case approaches to systems development.
ART-SCENE was developed by City University's Centre for HCI Design in London. Its origins were in the EU-funded Framework IV 21903 'CREWS' long-term research project. Since then ART-SCENE has been evaluated and extended in the UK EPSRC-funded SIMP project and bi-lateral projects, primarily with Eurocontrol and the UK's National Air Traffic Services.
Important ART-SCENE features include:
- simple-to-use tools for specifying and parsing Use Cases
- automatic generation of normal and alternative course scenarios from Use Case specifications
- guided scenario walk-throughs using Web-enabled tools
- multimedia representation of scenarios to improve discovery of requirements
- scenario walk-throughs on PDAs, to enable the walk-throughs to occur in the user's workplace
- support for standard requirements processes such as VOLERE
- specialisation of ART-SCENE to application domains
- process and facilitation guidelines for preparing and running ART-SCENE scenario workshops.
Typically, a project team using ART-SCENE writes Use Case specifications using ART-SCENE structured templates, style and content guidelines. This specification is then parameterised and parsed to enable ART-SCENE's two-step scenario generation algorithm to generate one or more scenarios.
In the first step, the algorithm generates normal course scenarios from the action-ordering rules and generation parameters in the Use Case specification. Each different possible ordering of normal course events is a different scenario. In the second step, the algorithm generates candidate alternative courses, which are expressed as 'what-if' questions for each normal course event, by querying a database containing over fifty different classes of abnormal behaviour and state in socio-technical systems. These classes are based on error taxonomies in the cognitive science, human-computer interaction and safety-critical disciplines. The algorithm generates, for example, alternative courses that describe events not occurring, actions not being completed, and human-agent mistakes, machine failures and interaction failures occurring. Examples are shown in the ART-SCENE example.
ART-SCENE delivers the generated scenarios with innovative Web-enabled tools such as the Scenario Presenter shown. The Scenario Presenter presents a scenario in four parts. The left-side menu provides different functions for viewing the scenario and the requirements generated for it. The top-line buttons offer walk-through functions (eg next or previous event) and functions to add, edit or delete events, comments and requirements. The left-hand main section describes the normal course event sequence for the scenario. Each event describes the start or end of an action, thus enabling a scenario to describe concurrent actions in this text-list form. The right-hand main section describes generated alternative courses for each normal course event, presented in the form of 'what-if' questions. Different alternative courses are presented for different normal course events.
Some of the most important features are accessed using the top-line buttons. Each major feature is available either for the selected event in the normal course (accessible above the normal course event sequence) or the selected alternative course (accessible above the alternative course list). The most important features are the add comment [C] and add requirement [R] features. A user can enter a comment or requirement associated with any normal or alternative course event at any time during a walkthrough. To add a requirement, the Scenario Presenter allows the user to specify the type, description, rationale and source of the requirement a subset of the VOLERE requirements shell.
So far, ART-SCENE has been successfully applied to specify several major air-traffic management systems, including Eurocontrol's Conflict Resolution Assistant and Departure Management systems, the latter in conjunction with the UK's National Air Traffic Services. We have also extended ART-SCENE through collaborations, in particular with the RWTH-Aachen in Germany to add multi-media functionality, and with Johannes Kepler University Linz in Austria to develop a PDA version of ART-SCENE. An ART-SCENE support team has been established at City University. New ART-SCENE development projects and roll-outs are currently being planned, and we welcome further opportunities to develop, evaluate and use ART-SCENE in requirements processes across Europe
Neil Maiden, City University, London, UK
Tel: +44 20 7040 8412