Modelling Human Factors using the Systems Modelling Language

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HFIDTC/2/WP2.8.9/1Version 2/ 24th September 2008Figure 7-25 - Requirements Diagram - Emergency EgressDiagram elements are as follows:• Use Case: The diagram includes the Use Case of interest, i.e. ‘Escape GCS’.• Requirement: The requirement is expressed as a stereotyped block, ‘EmergencyEgress’, including a text string detailing the requirement and the requirement IDnumber.• Block: This is a Block Definition Diagram showing the design of an escape hatch.• Relationships: Relationships between these features are shown by the dottedarrows linking the diagrams. The first, ‘trace’, shows how the requirement hasarisen from the Use Case. The second, ‘satisfy’, shows how the requirement issatisfied by the design.46
HFIDTC/2/WP2.8.9/1Version 2/ 24th September 2008• Satisfy Call Out: This call out shows other evidence that the requirement has beensatisfied, in this case in the form of documentation, i.e. the ‘Exit Procedure’ and‘Emergency Egress Study’.• Rationale Call Out: This call out shows the explanation as to how the ‘GCSEscape Hatch’ Block satisfies the requirement, i.e. that the design is consistentwith the applicable Defence Standard; in this case relating the size of the escapehatch to the anthropometrics in DEF STAN 00-25, ‘Physical Characteristics’.The ‘GCS Escape Hatch’ design block also shows the use of a constraint, showing thatthe space required is constrained by ‘escape hatch size’. We can then go on to definewhat this constraint is using parametric diagrams. Parametric diagrams are used torepresent real world constraints, e.g. the laws of physics. In this case we will express thatthe escape hatch size is constrained by the size of the human body.Figure 7-26 shows a Parametric Constraint Definition for escape hatch size expressed as aBlock Definition Diagram. The diagram features are as follows:• Title: In this case the ‘block’ is stereotyped as a , i.e. space area.• Constraint: Here the constraint properties are detailed, i.e. the formulae governingthe space required for the escape hatch; in this case the Area (A) is equal to theHeight (H) multiplied by the Width (W).• Parameter: The parameters are constraint ‘properties’; a constraint must always bebound to a property. In this case we define the parameters as Area, Height andWidth.Figure 7-26 - Parametric Constraint DefinitionNow that the parametric constraint has been defined we can express how it should beused, i.e. what the parameter should be. Figure 7-27 shows a Parametric Constraint UsageDiagram.47
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Modelling Human Factors using the Systems Modelling Language

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