Sander Bosman, Theo
van der Weide
Computing Science Institute, University of Nijmegen, The Netherlands
Information modeling is one of the main tasks during requirements engineering. Its result is a concise overview of concepts and their relations as they occur in the application domain under consideration (Universe of Discourse, UoD). This overview is called the information structure, and can be seen as a model of the UoD. During information modeling, two roles can be distinguished, referred to as domain expert and system analyst. The specification of the information structure forms both the basis for and the subject of understanding and communication between domain expert and system analyst.
In this paper we focus on natural language based modeling techniques. Such techniques aim at modeling how the UoD is communicated about; the resulting information structure is called the information grammar. Examples are NIAM  and PSM . From the information grammar the concrete information structures are readily derived. Note that other information modeling techniques (such as UML  and ER ) focus on this concrete information structure, thereby abstracting from the linguistic packing of the information. However, conserving the linguistic packing (information grammar) allows a discussion in terms of the natural concepts in the UoD.
Our aim is to propose the introduction of vague concepts: concepts which are recognized as important in the modeling process, but yet have no complete and formal specification of meaning. The intention of the modeling process is to construct a precise (as opposed to vague) specification. During modeling, vague concepts will be subject to further refinement.
Before introducing these vague concepts, we first take a fundamental look at the modeling process as consisting of two main activities: 1) providing domain knowledge, and, 2) processing (modeling) the provided knowledge. For convenience, as mentioned above, we will assume these actions will be performed by two separate persons: domain expert and system analyst. The aim is to work towards a method that lets a person create a formal model by starting with vague informal descriptions, and incrementally making these more formal until a clear, consistent and precise model results. Finally, we draw some conclusions.
In this paper, we are interested in the modeling process as an interaction between domain expert and system analyst. In this section, we will first focus on general communication between human beings. Then, we will discuss how information modeling can be seen as finding the information grammar of the communication between domain expert and system analyst.
Consider the situation where the domain
expert watches the UoD and
wants to communicate information about this UoD. As this involves
processes that occur inside a human's mind/brain (and are therefore
largely unknown), we adopt a rather abstract cognitive model of how
this works (see figure 1), based on
The collection of conceptions that describes (part of) the UoD is called the mental model of this UoD. Each conception can be said to model some aspect of the UoD, at some level of abstraction.
We do not assume that mental models are complete and consistent representations of the UoD. More typically, a mental model has a level of completeness and consistency good enough for its use.
Derivation of properties may also be influenced by the characteristics of the communication channel on which the properties will be represented. For example, in direct communication such as face-to-face speech it makes sense to communicate 'small' properties, allowing for interruption. When writing a document, a person will focus on properties on a higher level of abstraction.
A common way for humans to construct statements is to formulate them in natural language. It has been postulated that verbal communication still dominates these other styles of communication (the 'telephone heuristic', ). However, true as this may be, verbal communication is not always the most effective communication modality. This is why we allow graphical elements to be part of the communication.
Since the creation of representation
takes time, it is possible for
the UoD and its mental model perceived by the domain expert to change
while communicating statements. Suddenly a sequence of valid statements
may become invalid. The communicating person then has to 'invalidate'
the invalid statements.
As discussed in the previous section, the domain expert perceives the UoD and has a mental model of it. The expertise of the domain expert consists of having thorough knowledge of the UoD, and being able to communicate this model. The domain expert does not need to have the skills of providing a well abstracted model .
The domain expert communicates
statements about the UoD, to be
interpreted by the system analyst. The system analyst, in turn, can
respond with remarks (e.g., questions). This results in a sequence of
statements, referred to as the informal specification :
Goal of this communication is to create an informal specification that represents the mental model of the domain expert. We assume transitivity of the relation between UoD and mental model of the domain expert, and the relation between this mental model and the informal specification. This allows us to view the informal specification as a model of the UoD.
A model is a purposely abstracted, clear, precise and unambiguous conception.We will use the term in the following way:
Using a model as substitute for a UoD is the main reason for creating a model, as the model provides more insight in the UoD. It allows the creation of a 'shadow' UoD, which can be questioned and examined more efficiently than the 'real' UoD.
Let the information language be the set of possible statements the domain expert can give about the UoD, which are relevant for his perspective on the UoD. Now we can describe the modeling goal for the system analyst as follows:
The creation of a formal model by the system analyst is equivalent to the finding of the information language. The information language has been found when the system analyst can produce all statements that the domain expert could have communicated.
To be able to talk about intermediate stages in the modeling process, we relax the necessary properties of a formal model. Modeling starts with an empty formal model. As statements are communicated, the intermediate formal model grows towards the final formal model.
The formal model is finished when it can produce the information language. Until then, some required statement may not be generated by the model. Alternatively, a generated statement may not be interpretable by the domain expert.
An extensional model has some disadvantages:
For these reasons, we limit formal models to be intensional models, containing the structure of the information language. This structure is called the information grammar. From the information grammar, all statements in the information language can be generated. The information grammar does not have the disadvantages of the extensional model: it is much more compact, and may even describe infinite information languages.
The task of the system analyst can now be described in further detail:
The task of the system analyst is to create an intensional formal model from the informal specification. This involves finding structure in the informal specification, as well as obtaining or inducing additional information that is not part of the informal specification.
The need to obtain or induce additional information is a direct result of the assumption that the informal specification may be an incomplete extensional model. Although induction may be performed by the system analyst, we assume information about the structure of the information language can be obtained from the domain expert:
Note that this does not imply the domain expert can directly give the complete structure of the information language. Typically, the domain expert will give 'pieces of the puzzle' that are analyzed and combined by the system analyst.
We can now distinguish two types of statements communicated by the domain expert:
The communicative behavior of the system analyst is determined by the task to construct a complete and consistent formal model . The system analyst may exhibit the following two extreme types of behavior: awaiting and strict.
This behavior has several disadvantages:
A new sentence has to fit nicely in the current formal model, otherwise the system analyst will try to revise the formal model immediately, or has to refuse to incorporate the statement.
We introduce vague concepts as a means for obtaining the behavior sketched above. Vague concepts are concepts or concept structures that are probably important for the final formal model, but for some reason do not fit into the current formal model. They have to be remembered, and opportunities have to be awaited or created which allow the concepts to become part of the final formal model.
In our future research we will try to further develop a theory concerning vague concepts in formal information modeling, as well as describe ways in which vague concepts can incrementally be made precise as part of the final formal model.