Functional flow block diagram: Difference between revisions

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{{Short description|Flow Diagram}}

[[Image:Functional Flow Block Diagram Format.jpg|thumb|420px|Figure 1: Functional Flowflow Blockblock Diagramdiagram Formatformat.<ref name="SEF01">[http://www.dau.mil/pubscats/Pages/sys_eng_fund.aspx ''Systems Engineering Fundamentals.''] {{webarchive|url=https://web.archive.org/web/20110728000913/http://www.dau.mil/pubscats/Pages/sys_eng_fund.aspx |date=2011-07-28 }} Defense Acquisition University Press, 2001</ref>]]

A '''Functionalfunctional Flowflow Blockblock Diagramdiagram''' ('''FFBD''') is a multi-tier, time-sequenced, step-by-step flow diagram of a [[system]]’s's functional flow.<ref>The first version of this article is completely based on the [http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/operations/sysengsaf/seman/SEM3.1/Section%204.4.pdf NAS SYSTEM ENGINEERING MANUAL SECTION] 4.4 VERSION 3.1 06/06/06.</ref> The term "functional" in this context is different from its use in [[functional programming]] or in mathematics, where pairing "functional" with "flow" would be ambiguous. Here, "functional flow" pertains to the sequencing of operations, with "flow" arrows expressing dependence on the success of prior operations. FFBDs may also express input and output data dependencies between functional blocks, as shown in figures below, but FFBDs primarily focus on sequencing.

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 chart]]s, [[data flow diagram]]s, [[control flow diagram]]s, [[Gantt chart]]s, [[PERT]] diagrams, and [[IDEF]].<ref name="TD03">Thomas Dufresne & James Martin (2003). [http://mason.gmu.edu/~tdufresn/paper.doc "Process Modeling for E-Business"] {{webarchive |url=https://web.archive.org/web/20061220024049/http://mason.gmu.edu/~tdufresn/paper.doc |date=December 20, 2006 }}. INFS 770 Methods for Information Systems Engineering: Knowledge Management and E-Business. Spring 2003</ref>

FFBDs are also referred to as ''Functional'functional Flowflow Diagramsdiagrams''', '''functional block diagrams''', and '''functional flows'''.<ref name="FAA08"/>

== History ==

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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|Lake Placid]], [[New York (state)|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, [[Benjamin S. Graham|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.<ref name="BBG02"/>

The modern Functional Flow Block Diagram was developed by [[TRW Inc.|TRW]] Incorporated, a defense-related business, in the 1950s.<ref>Tim Weilkiens (2008). ''Systems Engineering with SysML/UML: Modeling, Analysis, Design''. Page 287257.</ref> In the 1960s it was exploited by [[NASA]] to visualize the time sequence of events in space systems and flight missions.<ref>[[Harold Chestnut]] (1967). ''Systems Engineering Methods''. Page 254.</ref> FFBDs became widely used in classical [[systems engineering]] to show the order of execution of system functions.<ref name="TD03"/>

== Development of functional flow block diagrams ==

[[Image:Development of Functional Flow Block Diagrams.jpg|thumb|right|240px|Figure 2: Development of Functionalfunctional Flowflow Blockblock Diagramsdiagrams<ref name="NASA07">NASA (2007). ''[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080008301_2008008500.pdf NASA Systems Engineering Handbook]'' December 2007. p.53.</ref>]]

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.<ref name="NASA07"/>

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* ''Function block'': Each function on an FFBD should be separate and be represented by single box (solid line). Each function needs to stand for definite, finite, discrete action to be accomplished by system elements.

* ''Function numbering'': Each level should have a consistent number scheme and provide information concerning function origin. These numbers establish identification and relationships that will carry through all Functional Analysis and Allocation activities and facilitate traceability from lower to top levels.

* ''Functional reference'': Each diagram should contain a reference to other functional diagrams by using a functional title reference (box in brackets).

* ''Flow connection'': Lines connecting functions should only indicate function flow and not a lapse in time or intermediate activity.

* ''Flow direction'': Diagrams should be laid out so that the flow direction is generally from left to right. Arrows are often used to indicate functional flows.

* ''Summing gatesgate'': A circle is used to denote a summing gate and is used when AND/OR is present. AND is used to indicate parallel functions and all conditions must be satisfied to proceed. OR is used to indicate that alternative paths can be satisfied to proceed.

* ''GO and NO-GO pathspath'': “G” and “bar G” are used to denote “go” and “no-go” conditions. These symbols are placed adjacent to lines leaving a particular function to indicate alternative paths.

=== Function symbolism ===

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{| class="vatop" style="width:100%;"

|[[Image:3 Function Symbol.jpg|thumb|center|360px|Figure 3. Function Symbolsymbol]]

|[[Image:4 Directed Lines.jpg|thumb|center|360px|Figure 4. Directed Lineslines]]

|}

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A line with a single arrowhead shall depict functional flow from left to right, see Figure 4.<ref name="FAA06"/>

=== Logic Symbolssymbols ===

The following basic logic symbols shall be used.<ref name="FAA06"/>

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{| class="vatop" style="width:100%;"

|[[Image:5 AND Symbol.jpg|thumb|center|360px|Figure 5. "AND" Symbolsymbol]]

|[[Image:6 Exclusive OR Symbol.jpg|thumb|center|360px|Figure 6. "Exclusive OR" Symbol]]

|}

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* Inclusive OR: A condition in which one, some, or all of the multiple preceding or succeeding paths are required. Figure 7 depicts Inclusive OR logic using a combination of the AND symbol (Figure 5) and the Exclusive OR symbol (Figure 6). Read Figure 7 as follows: F2 OR F3 (exclusively) may begin after completion of F1, OR (again exclusive) F2 AND F3 may begin after completion of F1. Likewise, F4 may begin after completion of either F2 OR F3 (exclusively), OR (again exclusive) F4 may begin after completion of both F2 AND F3

[[Image:7 Inclusive OR Logic.png|thumb|center|360px|Figure 7. “Inclusive"Inclusive OR”OR" Logiclogic]]

=== Contextual and Administrativeadministrative Datadata ===

Each FFBD shall contain the following contextual and administrative data:<ref name="FAA06"/>

* Date the diagram was created

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{| class="vatop" style="width:100%;"

|[[Image:8 FFBD Function 0 Illustration.jpg|thumb|center|360px|Figure 8. FFBD Function 0 Illustrationillustration]]

|[[Image:9 FFBD Function 2 Illustration.jpg|thumb|center|360px|Figure 9. FFBD Function 2 Illustrationillustration]]

|}

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* [[Activity diagram]]

* [[Block diagram]]

* [[Business Processprocess Mappingmapping]]

* [[Dataflow]]

* [[Data and information visualization]]

* [[DRAKON]]

* [[Flow diagram]]

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== Further reading ==

{{commons category|Functional flow block diagrams}}

* DAU (2001) [https://web.archive.org/web/20170131231503/http://www.dau.mil/publications/publicationsDocspublicationsdocs/SEFGuidesefguide%2001-01.pdf ''Systems Engineering Fundamentals.''] Defense Acquisition University Press.

* FAA (2007) [http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/operations/sysengsaf/seman/ System Engineering Manual]. Federal Aviation Administration Washington.

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[[Category:Diagrams]]

[[Category:Systems analysis]]

[[Category:Modeling languages]]