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A function model or ''functional model'' in systems engineering and software engineering is a structured representation of the functions (activities, actions, processes, operations) within the modeled system or subject area.〔(FIPS Publication 183 ) released of IDEFØ December 1993 by the Computer Systems Laboratory of the National Institute of Standards and Technology (NIST).〕 A function model, similar with the activity model or process model, is a graphical representation of an enterprise's function within a defined scope. The purposes of the function model are to describe the functions and processes, assist with discovery of information needs, help identify opportunities, and establish a basis for determining product and service costs.〔(Reader's Guide to IDEF0 Function Models ). Accessed 27 Nov 2008.〕 == History == The function model in the field of systems engineering and software engineering originates in the 1950s and 1960s, but the origin of functional modelling of organizational activity goes back to the late 19th century. In the late 19th century the first diagrams appeared that pictured business activities, actions, processes, or operations, and in the first half of the 20th century the first structured methods for documenting business process activities emerged. One of those methods was the flow process chart, introduced by Frank Gilbreth to members of American Society of Mechanical Engineers (ASME) in 1921 with the presentation, entitled “Process Charts—First Steps in Finding the One Best Way”.〔Ben B. Graham (2002). ''Detail Process Charting''. p.2.〕 Gilbreth's tools quickly found their way into industrial engineering curricula. The emerge of the field of ''systems engineering'' can be traced back to Bell Telephone Laboratories in the 1940s. The need to identify and manipulate the properties of a system as a whole, which in complex engineering projects may greatly differ from the sum of the parts' properties, motivated various industries to apply the discipline. One of the first to define the function model in this field was the British engineer William Gosling. In his book ''The design of engineering systems'' (1962, p. 25) he stated: :''A functional model must thus achieve two aims in order to be of use. It must furnish a throughput description mechanics capable of completely defining the first and last throughput states, and perhaps some of the intervening states. It must also offer some means by which any input, correctly described in terms of this mechanics, can be used to generate an output which is an equally correct description of the output which the actual system would have given for the input concerned. It may also be noted that there are two other things which a functional model may do, but which are not necessary to all functional models. Thus such a system may, but need not, describe the system throughputs other than at the input and output, and it may also contain a description of the operation which each element carries out on the throughput, but once again this is not.''〔William Gosling (1962) ''The design of engineering systems''. p. 23〕 One of the first well defined function models, was the Functional Flow Block Diagram (FFBD) developed by the defense-related TRW Incorporated in the 1950s.〔Tim Weilkiens (2008). ''Systems Engineering with SysML/UML: Modeling, Analysis, Design''. Page 287.〕 In the 1960s it was exploited by the NASA to visualize the time sequence of events in a space systems and flight missions.〔Harold Chestnut (1967). ''Systems Engineering Methods''. Page 254.〕 It is further widely used in classical systems engineering to show the order of execution of system functions.〔Thomas Dufresne & James Martin (2003). ("Process Modeling for E-Business" ). INFS 770 Methods for Information Systems Engineering: Knowledge Management and E-Business. Spring 2003〕 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「function model」の詳細全文を読む スポンサード リンク
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