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 flow block diagram format.<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>

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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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* [[Business process mapping]]

* [[Dataflow]]

* [[Data and information visualization]]

* [[DRAKON]]

* [[Flow diagram]]