It seems to me that the symbols for Internal Block Diagram and Block Definition Diagram are swapped. Here's an example of what a BDD should look like: https://i.imgur.com/dVg5NFi.png

Here's an example of what an IBD should look like: https://i.imgur.com/SudJpId.png

Also, when an "Instance Specification" is created (in a BDD which should be an IBD), ports from the block definition cannot be attached to it. So it's impossible to create a diagram like this: https://i.imgur.com/SudJpId.png

And one last question: How do you indicate the object instance count in the IBD. It should show as either a square bracket following the type name like this: https://i.imgur.com/YPkN92G.png

14 February 2018 19:14:39 Ali Ghorashi

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Ali Ghorashi 15 February 2018 23:07:32

BDD and IBD Swapped

Just noticed that the IBD diagram icon shows the correct symbols (object instance and interface ports).

Dusan Rodina - softwareideas.net 16 February 2018 9:43:54


I reviewed the diagrams, the symbols seem to be correct, as you mentioned in the second comment. However, there will be some improvements in these diagrams in the next version. Additional (missing) attributes will be added to the Property element.

Ali Ghorashi 16 February 2018 17:01:26


Hi Dusan,

Thanks for your response. Maybe I'm missing something but I'm quite sure they are backwards in the program. I double checked in two SysML books. Also here's a link to a short SysML tutorial: http://www.omgsysml.org/SysML_Modelling_Language_explained-finance.pdf

A Block Definition Diagram is similar to a UML class diagram. It only defines the blocks and their properties (see pp5 in the reference). So it only needs to have block definitions, aggregation relationships, generalizations, etc . Which is exactly what the current Internal Block Diagram palate has.

An internal block diagram is a little more like an Activity Diagram where instances of the blocks defined in the Block Definition Diagram are shown along with the data flow between them through their ports.

Here's an excerpt from the "SysML Distilled" book about blocks: https://i.imgur.com/0EKPc1e.png

Here's a link to another SysML book I found online: http://tinyurl.com/yaf6vmw3

See Appendix A4 on page 594

If you have any references that counter my understanding, please let me know.


Ali Ghorashi 16 February 2018 17:27:38


Forgot to mention Section 8.2.1 for BDD and Section 8.2.2 for IBD of the UML Spec 1.4: https://www.omg.org/spec/SysML/1.4/PDF

Thanks again.

Dusan Rodina - softwareideas.net 16 February 2018 17:28:35


Hi Ali,

You are right, SysML needs to be updated and enhanced in the program. The next versions will bring improvements to SysML in Software Ideas Modeler.

Ali Ghorashi 16 February 2018 18:39:23


Great. Keep up the good work. When is the next rev due for release?

Dusan Rodina - softwareideas.net 19 February 2018 10:24:07


Thank you. I assume it could be completed this week.