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Requirements Model

Revision as of 10:44, 29 December 2008 by (Talk | contribs) (Current questions)

< To: ORMF


This page describes the new requirements model, which is now based on the EMF framework. The model is currently defined only at a high level and will iteratively refine over the course of the next few weeks.

The high level view of the model

The figure below shows the initial high level analysis model for the ORMF requirements. At this stage the model simply reflects the main elements and their mutual relationships.

Emf model.gif

Requirement Artefact

At the highest level of abstraction we have the Requirement Artefact, which represents all general features that are shared by all types of requirements. The Requirement Artefact has two specialisations, namely the Requirement and the Requirement Narrative elements.


The Requirement element represents standard requirements, which can then be further specialised into Functional Requirements or Non Functional Requirements. Requirements may be specified by other Requirements, in a parent/child relationship.

Requirement Narrative

Requirement Narrative elements are types of Requirements Artefacts that expect descriptive elements, such as flows of events. A Requirement may be associated with (and traceable to) a Requirement Narrative element. Special cases of Requirement Narratives are User Story and Use Case elements. A Use Case element in particular may have associations with (refer to) a number of Actor elements and zero or one Use Case Package element.

Requirement Elucidator

Any Requirement Artefact element may then contain a number of relationships to Requirement Elucidator elements. Requirement Elucidators are elements that may be utilised across a number of different types of Requirement Artefacts and that permeate the entire requirements model. Examples of Requirements Elucidators are Issues, Glossary Terms and Notes. The distinguishing features of Requirements Elucidator elements are a) the fact that each Elucidator may be referred to by multiple Requirements Artefacts (f.i. a Note may be related to, or elucidate, any number of Requirements Artefacts) and b) the fact that it is possible to compile lists of all Elucidators of a given type defined across the entire requirements model through generic reporting tools.

The model shows all the types of Requirement Elucidators we intend to support.


Any Requirement Artefact element is characterised by relationships with either other Requirement Artefacts (named “requirement relationships” in the model) or Requirement Elucidators (named “elucidator relationships” in the model). These relationships have many features in common, such as their stereotype, which defines the type of Requirement Artefact or Requirement Elucidator that is referred to as the target of the association, or their multiplicity. As such, these associations could be described by a common association class, generically called Relationship. The problem with doing this is that EMF does not support association classes. This is the reason why the Relationship element shown in the model is currently sitting in a corner as a simple reminder.

Requirement Document and Augmentation Text

The model finally defines two other types of elements, namely Requirement Document and Augmentation Text.

A Requirement Document represents a textual artefacts that acts as a “wrapper” around specific sub sets of Requirement Artefacts. A good example of this type of element is the Software Requirements Specification document, which is typically a high level survey of all functional, non functional and use case related requirements for a software project or for a specific component of the project. The analyst typically organises the survey in a particular way, that needs to be reproducible through the natural evolution of the requirements and that needs to contain sections of descriptive text that acts as a cohesive agent for all requirement artefacts proper. Examples of such sections are introduction, overview of the problem domain etc. This text is what the model refers to as Augmentation Text, which is represented as a separate model element; any Requirement Document makes use of an arbitrary number of Augmentation Text elements.

Current questions

  1. How to represent the association class Relationship in EMF?


Please enter comments below by selecting the edit icon to the right. You will need a Bugzilla account to add comments.

Nitpicking: The Requirements parent/child relation should have a cardinality of 0..1:0..*

I just realized that I might have mismatched the cardinalities of parent/child and Requirement/Requirement Narrative. Would you please attach the model files to this page so we can look at the details directly.

I'm quite sure that Requirement, Requirement Narrative, Req Artifact and Req Elucidator are abstract classes. I for one like this information in the model, but this is a matter of personal preferences. 08:42, 26 December 2008 (UTC)

I would like to suggest an important refinement: requirement versions Actually, every artefact any role will produce will actually be some version of that artefact, which, as far as I understand, ORMF will have to be able to deal with.

Another question is, why parent-child relationships between requirements are modeled explicitly when the model already contains the more generic "req relationships" relation on the Req Artefact level. Consequently, that generic relationship should be expressed using the Relationship class from which more specific relationships can be derived.

One more minor point for a suggestion would be to include "Design Constraint" or another, more general, constraint class as specialization of Requirement into the model, since constraints are a frequent thing to deal with in specifications. Constraints do not always map onto non functionals, so I would not treat them as specializations of the Non Functional class.

I am not sure, if it is wise to restrict the ability of packaging to Use Cases alone. I have worked with requirements packages quite effectively in the past. Maybe we should allow any Req Artefact to be packaged?

Another interesting point is the level of modeling abstraction covered here. If we view the requirements process from some distance away, it usually starts with some business vision or broad goals. These goals are often refined into capabilities required to achieve those goals, which are then captured in business rules or business processes (or simpler flows). To my understanding, these elements are as important as Use Cases or User Stories and provide similar information (just on a different level). I therefore would kindly ask you to explain why Use Cases and User Stories are children of Requirements Narrative, while Vision and Goals are missing and Business Rules and Flows (or processes) are only elucidators? I am not sure if I have understood the difference between elucidator and narrative properly. 09:42, 29 December 2008 (UTC)

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