IBD: Context for SimpleDomesticInverterAirCon

This Internal Block Diagram (IBD) shows a usage of the «system» block SimpleDomesticInverterAirCon within the «system context» block SimpleDomesticInverterAirConContext, along with usages of a block External representing the outdoor environment and a usage of an air-conditioned IndoorSpace:

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This is not quite a black box view, because it exposes the :parts compartment of SimpleDomesticInverterAirCon. We'll drill down into more of the internal details later.

Speaking of black boxes, notice how there is a Connector across the block boundary of :IndoorSpace from the output Port of its :TemperatureSensor to an input Port of :SimpleDomesticInverterAirCon. You can do this (it's allowed in SysML) but long term it's not always such a good idea:

Webel Best Practice: Progressively "exporting" internal Ports of usages of Blocks to the boundary of their using Block may seem like a bit of extra work, but it means you can progressively develop with clean black box views without the Connectors crossing Block boundaries.

MagicDraw SysML/Cameo has a nice feature 'Tools > Delegate Port(s)' accessible from the context menu for splitting Connectors that cross block boundaries into multiple Connectors with "exporting" Ports.

This diagram only shows the Port names, it does not show the Port types (we'll see them progressively introduced in later slides). Note the Port naming pattern:

Webel Best Practice: Webel: If you must name your Ports or Pins, name them simply 'i', 'o', or 'io' (or 'oi') to indicate direction UNLESS you have to indicate a special role like 'iRole', 'oAuxiliary'. DO NOT use Port or Pin names like 'input', 'output', etc.

We can, however, tell from the little direction indicator arrows inside the Port rectangles that every Port type used here has at least one FlowProperty defined on it.

There are some simple "InformationFlow-style" ItemFlows for Air, TemperatureReading, and SineWavePower, each just conveying a Classifier (without a SysML ItemFlow::itemProperty).

One has to be careful not to over-interpret boundaries of Blocks as physical constructs; typically they primarily represent contracts between the connected Ports:

SysML: The placement of usages of Blocks, their Ports, and Connectors in an Internal Block Diagrams DOES NOT necessarily represent physical geometry!

In the example here, it is not specified whether the air conditioner is a split commercial air conditioning system or a single domestic unit stuck halfway through the window or wall of house (with the back facing the external environment). From the point of view of the flows in the model it does not matter!

Dr Darren says:

My father was a sparky, and amongst other things installed domestic air conditioning units. I once helped him knock a hole through a wall of a customer's house (mostly I just had to help clean up the mess of rubble afterwards).

Let's now see how the underlying SysML machinery that enables us to construct such an Internal Block Diagram (IBD) is setup.

Up next

Package Diagram overview of a simple domestic air conditioner with an inverter

Notes

[CAVEAT, MODELLING]{INFORMATIVE} Dependency/Usage relationships in some referenced UML/SysML diagrams on this site are for educational illustration only, they are NOT part of the actual model.

[CONVENTION, MODELLING, NAMING, TIP]{STRONG} Webel: If you must name your Ports or Pins, name them simply 'i', 'o', or 'io' (or 'oi') to indicate direction UNLESS you have to indicate a special role like 'iRole', 'oAuxiliary'. DO NOT use Port or Pin names like 'input', 'output', etc.

[MODELLING, STYLE, TIP] Progressively "exporting" internal Ports of usages of Blocks to the boundary of their using Block may seem like a bit of extra work, but it means you can progressively develop with clean black box views without the Connectors crossing Block boundaries.

[MODELLING, STYLE, TIP, TOOL]{INFORMATIVE} MagicDraw SysML/Cameo has a nice feature 'Tools > Delegate Port(s)' accessible from the context menu for splitting Connectors that cross block boundaries into multiple Connectors with "exporting" Ports.

[ASSERTION, TOOL] SysML: The «system», «subsystem», «external», «domain» and «system context» keywords are for "user defined" block Stereotypes (they are not part of core SysML); they are supported in MagicDraw/Cameo as Non-Normative Extensions.

[GOTCHA, MODELLING, WARNING]{STRONG} SysML: The placement of usages of Blocks, their Ports, and Connectors in an Internal Block Diagrams DOES NOT necessarily represent physical geometry!

Snippets (quotes/extracts)

[SysML-1.6] The «system» and «external» stereotypes are user defined, not specified in SysML, but help the modeler to identify the system of interest relative to its environment.