## 6 Requirements Management with a Graph-Based Design Language
### A General Model of Requirements in a Graph-Based Design Language  
One main condition for the approach to connect requirements with the product, which is shown here, is a requirement model. In this case, it is a requirement model created by a graph-based design language (Figure 13). The class diagram shown in Figure 13 consists of a main class named \"Requirement\" that includes attributes ID, Name, Description, Version, Status, Unit, Value, Comment, RelatedToPart, and RelatedToRequirement (will be used for structuring requirements). Each of the requirements in the database that was created from requirements in the company (compare Section 4.2) was taken into account and was illustrated by model in the graph-based design language. Consequently, these requirements could be shown as \"Requirement\" instances within the design graph after the compilation of the model (compare Figures 10 and 12). According to [PERSON] [46], requirements are supposed to have further attributes such as \"evaluation criterion\", \"possible characteristics\", \"desired characteristics\", \"weighting\" (prioritization), and \"actual characteristics\". Assigning content values to these attributes has to be done by engineering knowledge (experience) during the requirement collection phase. Figure 12: Graph of instances which represent the components of one typical variant of gear system (Instance attributes: z = number of teeth; mn = normal moduli; b = width). Furthermore, Figure 13 contains a class \"Mission\" that has an association to class \"Requirement\". \"Requirement\" is associated to \"Stakeholder\" with classes \"Contractor\" and \"Customer\". Both inherit from \"Stakeholder\" by specialization. In contrast to the model for gear systems, in which classes are determined by decomposition of a given product model (compare Section 5), the classes for requirements management are determined according to taxonomies which can be derived from literature (compare Section 4.1). That leads to a class diagram which contains several approaches for classifying requirements (Figure 13; colors represent taxonomies) additional to the general description of requirement entities. The classification of requirements in model-based requirements management is in general similar to existing requirements management systems. Until now, four different taxonomies are implemented (compare Figure 13). The first taxonomy considers the aspect of general type, implemented by the yellow classes \"FunctionalRequirement\", \"QualityRequirement\", and \"StructuralRequirement\". The second taxonomy takes the solution dependence into account by implementation of green domains \"GoalOrientedRequirement\", \"ScenarioOrientedRequirement\", and \"SolutionOrientedRequirement\". According to Figure 8, requirements can be classified by a third taxonomy, which is shown by orange colored domains (\"OnlyTechnicalRequirement\", \"TechnicalSurrounding\", \"HumanSocietyEnvironment\", \"Costs\", \"LawsNormsPatentsWarranties\", \"Time\", \"Staff\", and \"Aids\"). [PERSON] et al. [14] propose a further taxonomy (\"Geometry-\", \"Kinematics-\", \"Forces-\", \"Energy-\", \"Production-\", \"Material-\", \"Signals-\", \"Safety-\", \"Ergonomic-\", \"Qualitycontrol-\", \"Assembly-\", \"Transport-\", \"Operation-\", \"Maintenance-\", \"Recycling-\". \"Cost-\", and \"SchedulesRequirement\"), which is mostly utilized in checklists for conceptual design (highlighted by red color in Figure 12). The vocabulary in Figure 13 includes all four taxonomies. However, the experience during the modeling of the gear system (compare Section 7) shows that the taxonomy introduced by [PERSON] et al. [14] seems to be most appropriate for classification within the described design context. Further work will also look into further taxonomies, such as the categorization model presented by [PERSON] and [PERSON] [23]. A further purpose of a model of requirements in a graph-based design language can be the structuring of requirements (compare Section 4.1).