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A Functional Flow Block Diagram (FFBD) is a multi-tier, time-sequenced, step-by-step flow diagram of a system’s functional flow.〔The first version of this article is completely based on the (NAS SYSTEM ENGINEERING MANUAL SECTION ) 4.4 VERSION 3.1 06/06/06.〕 The FFBD notation was developed in the 1950s, and is widely used in classical systems engineering. FFBDs are one of the classic business process modeling methodologies, along with flow charts, data flow diagrams, control flow diagrams, Gantt charts, PERT diagrams, and IDEF.〔 Thomas Dufresne & James Martin (2003). ("Process Modeling for E-Business" ). INFS 770 Methods for Information Systems Engineering: Knowledge Management and E-Business. Spring 2003〕 FFBDs are also referred to as ''Functional Flow Diagrams'', ''functional block diagrams'', and ''functional flows''.〔 == History == The first structured method for documenting process flow, the flow process chart, was introduced by Frank Gilbreth to members of American Society of Mechanical Engineers (ASME) in 1921 as the presentation “Process Charts—First Steps in Finding the One Best Way”.〔 Ben B. Graham (2004). ("Detail Process Charting: Speaking the Language of Process". ) p.1〕 Gilbreth's tools quickly found their way into industrial engineering curricula. In the early 1930s, an industrial engineer, Allan H. Mogensen began training business people in the use of some of the tools of industrial engineering at his Work Simplification Conferences in Lake Placid, New York. A 1944 graduate of Mogensen's class, Art Spinanger, took the tools back to Procter and Gamble where he developed their Deliberate Methods Change Program. Another 1944 graduate, Ben S. Graham, Director of Formcraft Engineering at Standard Register Industrial, adapted the flow process chart to information processing with his development of the multi-flow process chart to display multiple documents and their relationships. In 1947, ASME adopted a symbol set as the ASME Standard for Operation and Flow Process Charts, derived from Gilbreth's original work.〔 The modern Functional Flow Block Diagram was developed by TRW Incorporated, a defense-related business, in the 1950s.〔Tim Weilkiens (2008). ''Systems Engineering with SysML/UML: Modeling, Analysis, Design''. Page 287.〕 In the 1960s it was exploited by NASA to visualize the time sequence of events in space systems and flight missions.〔 Harold Chestnut (1967). ''Systems Engineering Methods''. Page 254.〕 FFBDs became widely used in classical systems engineering to show the order of execution of system functions.〔 == Development of functional flow block diagrams == FFBDs can be developed in a series of levels. FFBDs show the same tasks identified through functional decomposition and display them in their logical, sequential relationship. For example, the entire flight mission of a spacecraft can be defined in a top level FFBD, as shown in Figure 2. Each block in the first level diagram can then be expanded to a series of functions, as shown in the second level diagram for "perform mission operations." Note that the diagram shows both input (transfer to operational orbit) and output (transfer to space transportation system orbit), thus initiating the interface identification and control process. Each block in the second level diagram can be progressively developed into a series of functions, as shown in the third level diagram on Figure 2.〔 These diagrams are used both to develop requirements and to identify profitable trade studies. For example, does the spacecraft antenna acquire the tracking and data relay satellite (TDRS) only when the payload data are to be transmitted, or does it track TDRS continually to allow for the reception of emergency commands or transmission of emergency data? The FFBD also incorporates alternate and contingency operations, which improve the probability of mission success. The flow diagram provides an understanding of total operation of the system, serves as a basis for development of operational and contingency procedures, and pinpoints areas where changes in operational procedures could simplify the overall system operation. In certain cases, alternate FFBDs may be used to represent various means of satisfying a particular function until data are acquired, which permits selection among the alternatives.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「functional flow block diagram」の詳細全文を読む スポンサード リンク
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