BDD: Figure 60: Hydraulics blocks, ports, & component properties

Even though resistance:ViscousResistance is effectively a constant (as it is always computed from values that don't change with time) it is in fact handled like a variable via a Constraint (as we'll see also later ):


{resistance=(8*viscosity*length)/(3.1416*(radius^4))}

Some minor diagramming differences compared with the spec figure version:

- SysML Ports are used (instead of Association ends with composite aggregation and a user-defined «port» keyword).

- The context block ConnectedTanks is shown.

This is a nice expert tool tip:

MagicDraw/Cameo: If you want to show a Property or Port listed both in its corresponding compartment on a Class or Block symbol and as the end of an Association in the same diagram, set the display option Show Association Ends As Attributes/Ports to 'all'

It's done here so one can see the assignment of the InstanceSpecifications that carry the initial values for the components in the context of ConnectedTanks. Each InstanceSpecification is set as the defaultValue of a corresponding Property of ConnectedTanks; the values their Slots carry then become so-called initial values (a.k.a. context-specific values) for the corresponding value properties within the context block ConnectedTanks (as can be seen its IBD).

But this trail model handles some of the initial values differently, because the example as shown in the spec breaks the Single Source of Truth (SSOT) and Don't Repeat Yourself (DRY) principles:

Unless one tank is on the surface of the Earth and the other is on Neptune the value of gravity should probably always be the same for both Tank usages!

This might not matter for a spec example, but it does matter on real-world engineering projects!

Therefore, to show you how to get more reuse, in this trail version a direct defaultValue is declared on the value properties gravity (and similarly on fluidDensity) on the block Tank; only fluidLevel (which could definitely be initially different for each Tank usage) and tankSurfaceArea (which could potentially be different for each Tank usage) are handled using the additional Context-Specific Values mechanism.

(One could of course take this approach further and isolated gravity in a block of EarthSurfaceConstants, then assign that EarthSurfaceConstants::gravity as the defaultValue on gravity in an assumed earth-bound Tank.)

As indicated, there are a lot of additional user-defined ValueTypes and Units in this example that aren't available directly in the specified non-normative SysPhSLibrary ModelLibrary. (Some of them could of course also have been fetched from the ISO-80000 ModelLibrary.)

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IBD: Figure 59: Internal structure of hydraulics system

Notes

[DISPLAY, FEATURE, TOOL]{INFORMATIVE} MagicDraw/Cameo: If you want to show a Property or Port listed both in its corresponding compartment on a Class or Block symbol and as the end of an Association in the same diagram, set the display option Show Association Ends As Attributes/Ports to 'all'

[POLICY]{STRONG} About the Single Source of Truth (SSOT) and Don't Repeat Yourself (DRY) principles

[ANTI-PATTERN] SysPhS-1.1: In the specification model for Figure 59 the handling of the initial values for some value properties (such as for 'gravity') in Tank usages within context block ConnectedTanks is WET not DRY (breaks Single Source of Truth).

[ISSUE] SysPhS-1.1: p.81: 'resistance:ViscousResistance' (in Figure 60) has to be treated as a PhSVariable not a PhSConstant, otherwise get an invalid system with 6 variables and 7 equations.

[MODELLING, STYLE]{RECOMMENDED} Webel vs SysPhS-1.1: Recommend use standard SysML Ports instead of block part property with «port» keyword

[ANTI-PATTERN, ISSUE, WARNING]{INFORMATIVE} There is no «port» stereotype keyword for Port or Property in UML-2.5.1 or SysML-1.6. It is assumed to be introduced in some SysML and SysPhS specification diagrams as a custom or user-defined stereotype for special illustration purposes.

[ANTI-PATTERN, MODELLING] The use of an additional «port» keyword on a Port is usually redundant and causes clutter. The use of an additional «port» keyword on a basic Property is an obsolete trick. Please don't imitate it even if you see it in some specification sample diagrams!

Snippets (quotes/extracts)

[SysPhS-1.1] Figure 60 shows block definitions for components of ConnectedTanks in Figure 59.