It’s well known that scenarios, description of real world facts and actions, are very powerful in so far as they get stakeholders to immerse themselves and understand more a given process. Performing requirements engineering then without “inviting scenarios to the party” will be very arduous or almost beyond the bounds of feasibility. The main issue for scenario based approaches will then concern the way scenarios are designed and organized. The “scenario classification framework” is an attempt to solve that issue and to make scenarios more effective in the requirements engineering process. How does it work?
The framework proposes a classification of scenarios along four different views: form, contents, purpose and lifecycle. Each view is sliced in dimensions called facets, to which a list of attributes is attached. Thus, characterizing a given scenario foreshadows giving a value to each attribute in each facet, for each one of the framework’s views.
The form view emphasizes the way the scenario is expressed. This expression can be seen along two dimensions which are the description facet and the presentation facet. If the former one is measured by the level of formality and the channel used, respectively notation and medium attributes, the latter evaluates the liveliness of the scenario through animation and interactivity attributes.
On the contents axis, the framework enlightens scenarios along four different dimensions. The abstraction facet, expressing the concreteness of a scenario, is evaluated by Boolean values (instance, type, mixed) which indicate whether a scenario describes a specific experience or situation, a generic one, or both. Then, there is the context facet, which expresses the amount of information embedded in a scenario, relating to the context of the To Be system. This is performed by determining whether properties like the internal behavior of the system, interactions in terms or role playing with its environment, the organizational context of the system including the organization’s structure and the organizational environment are included in the relevant scenario or not. Another angle of scenario analysis along the contents axis is about the argumentation knowledge enunciated in the relevant scenario. There again, the duty is to check if the scenario includes descriptions of alternative positions, arguments that go along with a given position, conflicts or issues that may arise and final decisions or not. According to the kind of information captured by the scenario, a last clarification could be made: there lays the concern of the coverage facet. A scenario may capture functional aspects (structure, function and behavior) of the system as much as non functional ones (security, performance, time). Moreover, intentional aspects of systems like goals, problems and objectives are taken in account in that facet.
Scenarios can play different role according to intended ambition or expectation. The purpose view identifies those roles during the scenario classification process. Thus, scenarios may be descriptive regarding a given process, exploratory by investigating different ways to meet a requirement or explanatory by elucidating a pronounced issue.
The lifecycle view, the last one, investigates in one hand on scenario’s progression and lifetime, and in another hand on operations or transformation they might overcome. Thus, this view exposes two facets: The lifespan facet which will help separating transient scenarios from persistent ones and the operation facet for a classification according to the type of operation the scenario carry out. It could either be a capture operation through scenario generation from scratch or by reuse, or a refinement or restructuration operation. A scenario may also serve for assembly purpose and will then be classified in the integration operations category, or extend knowledge in an existing scenario and then be tagged as expansion operation type. Finally when a scenario reaches the end of its lifetime, deletion operations appear to be ineluctable.
Unfortunately, like many other approaches, this classification doesn’t tackle the process aspect of scenarios. Nevertheless, there have been some approaches to the process of scenario generation. These may include the use of business actors and responsibilities to discover use cases and then scenarios, or the use of a predefined matching between scenarios templates and types of situations.
Finally, from a practical point of view, the framework has proven usefulness after conducting polls on scenario characterization in industrial projects, although there’s still a gap between what’s stated in literature by research, and used tools and methodologies in experience.
An abstract by Lookman SANNI
Author: Colette ROLLAND