Beginners Guide to Model-Based Systems Engineering

12/18/2018

Items – The Second Dimension of Behavior

• Cross the system boundary • Passive things that are inputs and outputs of our system • Can be • Data • Signals • Physical objects

System

External System

input to/ triggers

performs

performs

Item

outputs

Top-Level

Top-Level

Function

Function

Item

outputs

input to/ triggers

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Reflecting the Two Dimensions: Functions & Items • Function • A process that transforms inputs into outputs • An action taken by the system or one of its elements • Represented by a verb or verb-noun pair • Data stores • Item that does not provide a control role • Defined by an input to relationship • Shown with a single arrowhead (EFFBD) or with “optional” annotation (activity diagram) • Triggers • Item that provides a control role • Defined by a triggers relationship • Shown with a double arrowhead (EFFBD) or without annotation (activity diagram) • Function enablement • Enabled upon completion of the function prior to it in the sequencing • Function execution • Requires enablement and triggering, if a trigger is defined

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