A Framework for Requirements Elicitation through Mixed-Initiative Dialogue Renaud Lecœuche Chris Mellish Dave Robertson [email protected] [email protected] [email protected] PSI-LIRINSA Department of Artificial Intelligence Universit´e de Rouen University of Edinburgh Mont-Saint-Aignan, France, 76130 Edinburgh, Scotland, EH1 1HN Abstract ine how the structure of requirements acquisition frame- works, which attempt to control the development of a re- In this paper we present our work on requirements elic- quirements specification, may be linked to the structure of itation. The elicitation process is a complex task which theories of dialogue, which attempt to control dialogue ac- necessitates computer support. Elicitation systems should cording to the conventions of discourse. ideally help their users check the correctness of the spec- Many approaches to the problem of natural language ifications obtained but also actively guide them in the ac- interaction for requirements elicitation have considered it quisition of the requirements. We consider hereafter sys- as a translation problem: the users write specifications in tems that communicate in natural language. We describe natural language and the system expresses them in a for- a framework that tries to improve the quality of the guid- mal framework [6, 7, 15, 16, 17, 26]. As the natural lan- ance it provides to its users by taking into account natural guage statements are directly and automatically translated language constraints. We discuss the need for a theory of into specifications that should ideally be consistent, com- natural language dialogue structure, and we show how we plete and coherent1, they should themselves have those have integrated such a theory within an early prototype of properties. If there are conflicts in the natural language an elicitation system. requirements, however, these may not be resolved because the system has no way of knowing what the user really Keywords: requirements elicitation, guidance, meant. As a result, the task of the user remains difficult. knowledge-based systems, natural language, mixed- Although the formal notation of the target framework is initiative, WWW hidden by the natural language, its constraints are still fully present and the user must consider them to write correct specifications. 1 Introduction In order to actively help users in the process of writ- Numerous frameworks, such as goal-oriented strate- ing the requirements, the elicitation system must interact gies [3], scenario-based strategies [12] and rapid prototyp- with them. The emphasis here is no longer on translating ing [1, 19, 8], have been suggested as aids to the acqui- requirements but on actively extracting them through dia- sition of software requirements. Much less attention has logue with the users. This task is complicated by the fact been paid to the control of dialogue taking place between that there are numerous ways of carrying out the require- the users and the system whilst using such frameworks ments elicitation. In other words the requirement frame- [2]. Our ability to develop sophisticated formal frame- works alone are not providing enough constraints to ensure works makes this deficiency more acutely felt, since in- a unique elicitation process. An arbitrary choice could be creases in formality are often accompanied by greater dif- made, but forcing the users to adopt a predefined method is ficulty in understanding and using the frameworks [22]. usually not possible as it would make the elicitation pro- Frameworks for requirements acquisition are not normally cess very difficult to follow and understand. The system accompanied by theories of the types of dialogue which must therefore be able to adapt itself to various elicitation they support. However, some theories of dialogue struc- 1The properties that requirements should exhibit are still a matter of ture are beginning to emerge, notably from the natural lan- debate [13]. The ones we cite are just used as examples. The point is guage processing community. It is interesting to exam- that, whatever the properties, the specifications are constrained. 189 methods. On the other hand it is necessary for the sys- ate. By structure, we mean the organisation of the site and tem to make choices in order to provide active guidance. the navigation constraints. This corresponds to the third A “least-commitment” strategy, such as asking the user at part of the usual decomposition of WWW sites in content, every choice point what to do next, is not a useful approach i.e., what is the site about, presentation, i.e., how is the in- [5]. One way of offering guidance without restricting the formation presented, and navigation, i.e., how users move users too much is by using natural language constraints between pages. (NLC) and mixed-initiative. NLCs ensure that the system This study has provided two interesting results: adopts a strategy that will guide the users in a natural and There are numerous ways of describing the require- understandable manner. Mixed-initiative ensures that the ments. Although the information conveyed in the dif- users can redirect the process and are not limited to a single ferent dialogues was basically the same the way it elicitation method. Using such an approach reduces some was elicited varied a lot. Every dialogue is organ- of the problems discussed above. The specifications do ised differently from the others. This confirms the not need to be immediately correct as they will be checked fact that numerous elicitation methods are possible. and reworked by the system. The formal framework is hidden from the user but is still there to ensure the cor- There are constraints on the structure of the dia- rectness of the specifications. Guidance is continuously logues. Although the dialogues were very different offered through dialogue, which is influenced by but does from one another, each of them presents a clear inter- not directly follow the steps of construction of the specifi- nal structure. cation. Moreover, because of the mixed-initiative, the user is still free to divert the course of dialogue by volunteering A system constraining the elicitation process to a strategic information. small set of predefined paths or a system oblivious of the dialogue structure would make the elicitation process dif- The integration of NLCs with requirements elicitation ficult for humans to follow. It is therefore necessary to rules requires two major steps. The first step consists in the take into account rules explaining dialogue structure. Fo- definition of the NLCs. NLCs related to mixed-initiative cus rules are such rules. dialogue have been studied by the natural language pro- Most focus theories are based on the notion of fo- cessing community since the ’70s. Different theories have cus space. A focus space contains what is important at been proposed. We will present them and explain how they a certain point in a dialogue, i.e., the things to which the can direct the dialogue between the users and the elicita- participants in a dialogue are attending. As the dialogue tion system. The second step consists in the actual integra- evolves, new focus spaces are created when new things tion of the NLCs in the requirements elicitation process. are discussed and then closed; or old focus spaces are re- The integration of these constraints with the requirements reopened when old things are re-introduced. Focus spaces elicitation constraints is a recent domain of research. We are organised in a stack [9] or a tree [14] or a more com- will present in detail our way of integrating the NLCs with plex structure [20] depending on the theory. the requirements elicitation process. The important point of these theories is that the evo- This paper is organised as follows. In section 2, we lution of the dialogue, i.e., the shifts between the different present some current dialogue theories and discuss how focus spaces, is constrained. For example, focus shifts can they can influence the dialogue between the users and the be constrained by the task to be achieved by the dialogue elicitation system. In section 3 we describe our system participants [9], the participants’ intentions [10], or the do- and how we have integrated the NLCs with the elicitation main structure [14]. By using these dialogue constraints process. We then show in section 4 how the system works we can define elicitation paths that are easily understood on some examples. In section 5 we compare our system by the users without restraining them to predefined paths. with related work. Finally we conclude in section 6 with There are a number of issues that we have to deal with some shortcomings of our approach and future work. and that are not clearly tackled by the focus theories: 2 Dialogue theory Re-opening closed focus spaces is not clearly ex- plained. We need however such rules if the users re- To study the structure of dialogues during the elici- alize that some requirements are incorrect and should tation task we have recorded several dialogues in the do- be reworked. main of research group WWW site construction. The par- ticipants in the dialogue are a WWW site expert acting as Linguistics phenomena marking the focus shifts in the elicitation system and a research group member acting the dialogue, such as cue words, are different from as the user of the system. The aim of the dialogue is to one theory to the other. However, without them the elicit the structure of the WWW site the user wants to cre- dialogue would be difficult for users to understand. 190 The shifts in focus also depend on domain proper- Specification model describes the entities that should be ties. For example, the shift to a link between pages elicited and their relations. It is currently based can only be done if there are at least two pages that on a domain-specific object-oriented framework: the already have been considered.