Countless Requirements. No Problem with a Requirements Diagram.

What is a requirements diagram, why is it important and what benefits does it offer?

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Requirements Diagram
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A requirements diagram visualizes requirements in a system as well as the relationships between different requirements and with other model elements.

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The types of relationships among elements can be seen and understood easily. In this example the requirement “calculating the optimal watering duration” is contained within the “module irrigation control system” requirement.

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Additional model elements like other diagrams or stakeholders with interest relationships increase the overall depth of understanding about the inter-relationships.

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A requirement does not just consist of one title, it also contains all the information and the relationships within the context.

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When test cases are displayed with their verify relationships it is easy to recognise if there are already test cases present for those specific requirements.

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Why are requirements important?

Requirements are of vital importance for every systems engineering process: Stakeholders have certain goals, and they hope to achieve these goals with the help of a (planned) system. To be able to do this, the system has to possess certain characteristics and features. The problem: Goals are too broad to derive specific system characteristics from these goals, and this is where requirements come in. Requirements concretize goals by describing in detail what features and characteristics a system must offer in order to satisfy the stakeholders.

Completeness, soundness and depth of detail are key when it comes to supporting other departments and disciplines partaking in the development process. In addition, disciplines such as systems architecture, design, implementation and testing are highly dependent from the requirements elicited as well as from their quality. The relevance of the requirements even goes beyond develpoment; activities like risk analysis, effort estimation maintenance and decomissioning are also based on the system requirements.

What is a requirements diagram?

The difference between textual elicitation of requirements and requirements diagrams is that diagrams allow for a significantly more structured and comprehensible way of illustrating requirements. Instead of compiling long and arduous lists, requirements engineers are able to model all relevant requirements in a way that is easily accessible for all project contributors. What is more, not only requirements are part of a requirements diagram, but also relationships to other elements. The example above shows a requirements diagram for an irrigation plant.

Apart from the requirement Module Irrigation Control System we see various subordinate requirements marked by a contain relationship. There are also two derived requirements connected to the original requirement by a derive relationship, as well as stakeholders, test cases and refinements in form of a block diagram.

What are the benefits of requirements diagrams?

The growing complexity of processes and operations makes it increasingly hard to understand their interconnections based on textual requirements. In contrast, requirements diagrams make all relationships between the different aspects of systems development transparent and accessible in a single diagram.

Visualizing requirements

The individual model elements of a requirements diagram offer instant access to the decisive aspects of the development process. At the same time they ensure traceability between these elements. Requirements are the perfect way of turning stakeholders’ goals into realizable models. From this, the entire development team benefits: All the features and characteristics of a planned system are easily communicable.