## 3 State of the Art
### Requirements Management  
#### 3.1.1 Research Activities Concerning Requirements Management  
An overwhelming amount of literature describing requirements management and requirements engineering can be found; it is therefore impossible to present a complete picture. A very good overview of earlier research can be found in [PERSON] and [PERSON] [6] and [PERSON] and [PERSON] [7]; current additions are shown, e.g., by [PERSON] et al. [8]. It is important to note that international standards which are concerned with requirements management also exist: most notable are the ISO standard 29148 \"Systems and software engineering--Life cycle processes--Requirements engineering\" [9] and the ISO standard 15288 [10] \"Systems and software engineering--Systems life cycle processes\", as well as the recently revised quality management norm ISO 9001 [11]. Furthermore, current research addresses frameworks for product lifecycle integration [8], requirements change prediction models [12],  
Figure 4: Research structure and structure of this paper. systematic determination of product properties [13], and requirements checklists [14]. More and more research is concerned with requirements management in industrial settings. Requirements can be defined as the purpose, goals, constraints, and criteria associated with a product development project [12]. These requirements may range from the initial functional requirements to the detailed specifications [15]. Several classification schemes for requirements were proposed in literature (compare [PERSON] and [PERSON] [16]). [PERSON] et al. [8] propose a lifecycle-view-based classification in only three categories: (1) BOL--Beginning of Life, including planning, design, and production) related requirement; (2) MOL--(Middle of Life, including use, service and maintenance) related requirement; and (3) EOL--(End of Life, including reuse, material reclamation and disposal) related requirements. A large body of research is concerned with the fuzzy front-end of product development: the transformation of the customer needs into requirements. Closely connected are approaches of qualitative and quantitative market research, which are often referred to as voice of the customer (VOC) studies. Early research reports in the 1990s [17] already identify four main aspects: customer needs, a hierarchical structure of the needs, priorities of the needs, and customer perceptions of performance. Several research studies are concerned with the integration of the voice of the customer into the subsequent processes of product development. For this integration, a number of models, methods, and tools were analyzed, such as the Kano model [18], CAD, and TRIZ [19], as well as virtual customer environments [20]. A focus on Collaborative Product Development/Definition and Management (CPDM) solutions for sharing, archiving, and managing customer needs (amongst other product information) can be identified as well (compare e.g., [21]). [PERSON] and [PERSON] [22] were able to establish categorization models of requirements which are based on a well-known model of human needs. The proposed categorization model supports elicitation of requirements and facilitates the detection of requirements that are not relevant to the system and of constraints that limit the solution trade-space without supporting the satisfaction of new needs. Several authors use the notion \"requirements engineering\". A number of different definitions exist which try to distinguish the notions of \"requirements engineering\" and \"requirements management\", but these terms can be used synonymously [17].