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I'm a bit confused about the concept of blocks in SysML.

From UML I understand that there is a distinction between classes and instances/objects like in OOP.

However, I'm not sure how this is implemented in SysML. My questions:

  • Does SysML distinguish between classes and instances?

  • Assume I want to describe a general type of sub-system e.g. a card reader. My system should include serval instances of indentical (or parameterized) card readers. How do I best model this in SysML.

  • Currently, I'm testing the SW Enterprise Architect. Is there anything special I have to consider if I want to model classes/instances here?

Thank you for your hints.

Joy
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BerndGit
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2 Answers2

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There is no difference between SysML and UML instances. In both cases an instance is shown with and underlined name. So what you see as blocks in SysML are simple stereotyped classes in UML. If you instantiate a block (in EA ctrl-drag it onto a diagram and select Instance) you get a concrete block. E.g. a block Car being instantiated becomes MyMercedes:Car (on the diagram showing with underlined text).

If you want to show real card readers, you create multiple instances. If you have different types of card readers you create different blocks which e.g. inherit from a basic card reader (there are different ways here).

Your last bullet point is too broad. Read the manual and look into Sparx' forum if you run into trouble (or ask here).

qwerty_so
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In SysML you have blocks ~ classes, and parts ~ attributes, where the SysML best practice does not aggregate blocks to blocks, i.e. when you describe subsystems you would display them as parts (instances of other blocks) of the main block.

Sam Ginrich
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