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 '''functional flow block diagram''' ('''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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== 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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{| 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 administrative data ===

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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]]