Requirements Development

This process area describes three types of requirements: customer requirements, product requirements, and product-component requirements. Taken together, these requirements address the needs of relevant stakeholders, including those pertinent to various product lifecycle phases (e.g., acceptance testing criteria) and product attributes (e.g., safety, reliability, maintainability). Requirements also address constraints caused by the selection of design solutions (e.g., integration of commercial off-the-shelf products).

Requirements are the basis for design. The development of requirements includes:

This process area addresses all customer requirements rather than only product-level requirements because the customer may also provide specific design requirements. Customer requirements are further refined into product and product component requirements. In addition to customer requirements, product and product-component requirements are derived from the selected design solutions.

Requirements are identified and refined throughout the phases of the product life cycle. Design decisions, subsequent corrective actions, and feedback during each phase of the product’s life cycle are analyzed for impact on derived and allocated requirements.

The Requirements Development process area includes three specific goals. The Develop Customer Requirements specific goal addresses defining a set of customer requirements to use in the development of product requirements. The Develop Product Requirements specific goal addresses defining a set of product or product-component requirements to use in the design of products and product components. The Analyze and Validate Requirements specific goal addresses the necessary analysis of customer, product, and product-component requirements to define, derive, and understand the requirements. The specific practices of the third specific goal are intended to assist the specific practices in the first two specific goals. The processes associated with the Requirements Development process area and those associated with the Technical Solution process area may interact recursively with one another.

Analyses are used to understand, define, and select the requirements at all levels from competing alternatives. These analyses include:

The definition of functionality, also referred to as “functional analysis,” is not the same as structured analysis in software development and does not presume a functionally oriented software design. In object-oriented software design, it relates to defining the services. The definition of functions, their logical groupings, and their association with requirements is referred to as a “functional architecture.”

Analyses occur recursively at successively more detailed layers of a product’s architecture until sufficient detail is available to enable detailed design, acquisition, and testing of the product to proceed. As a result of the analysis of requirements and the operational concept (including functionality, support, maintenance, and disposal), the manufacturing or production concept produces more derived requirements, including consideration of:

A hierarchy of logical entities (functions and sub-functions, object classes and subclasses) is established through iteration with the evolving operational concept. Requirements are refined, derived, and allocated to these logical entities. Requirements and logical entities are allocated to products, product components, people, associated processes, or services.

Involvement of relevant stakeholders in both requirements development and analysis gives them visibility into the evolution of requirements. This activity continually assures them that the requirements are being properly defined.