Traditionally, large projects have employed a document-based systems engineering approach. This approach is characterized by the generation of textual specifications and design documents, in hard-copy or electronic file format, that are then exchanged between customers. users , developers, and testers . System requirements and design information are expressed in these documents and drawings. The systems engineering emphasis is placed on controlling the documentation and ensuring the documents and drawings are valid, complete, and consistent, and that the developed system comp lies with the documentation. In the document-based approach, specifications for a particular system, its subsystems. and its hardware an d software components are usually depicted in a hierarchical tree, called a specification tree, A systems engineering management plan (SEMP) documents how the systems engineering process is employed on the project, and how the engineering disciplines work together to develop the documentation needed to satisfy the requirements in the specification tree. Systems engineering activities are planned by estimating the time and effort required to generate documentation, and progress is then measured by the state of completion of the documents.
Document-based systems engineering typically relies on a concept of operation document to define how the system is used to support the required mission or objective . Functional analysis is performed to allocate the top-level system functions to the components of the system. Drawing tools are used to capture the system design, such as the functional flow diagrams or schematic block diagrams.
These diagrams are stored as separate files and included in the system design documentation. Engineering trade studies and analyses are performed and documented by many different disciplines to evaluate and optimize alternative designs and allocate performance requirements. The analysis may be sup ported by individual analysis models for performance, reliability, safety, mass properties , and other aspects of the system.
Replaced/Superseded by document(s)
Systems engineering is a multidisciplinary approach for developing solutions to complex problems. The increase in system complexity is demanding more rigorous and formalized systems engineering practices. In response to this demand, along with advancements in computer technology, the practice of systems engineering is undergoing a fundamental transition from a document-based approach to a model-based approach. In the model-based approach, the emphasis shifts from producing and controlling documentation to producing and controlling a coherent model of the system. Model-based systems engineering (MBSE) can help to manage complexity, while at the same time improve design quality and cycle time, improve communications among a diverse development team, and facilitate knowledge capture and design evolution.