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Editorial Team
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Asked: 2026-06-04T21:06:45+00:00

Image the following: (<> indicates a black diamond, which refers to a composition in

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Image the following: (<> indicates a black diamond, which refers to a composition in UML)

+---+ 0..1   * +---+
| A |<>--------| B |
+---+          +---+

I have class A and class B. A containment reference exists from A to B with multiplicity unbound. The opposite reference has multiplicity 0..1.

My question is: Isn’t this opposite multiplicity wrong / impossible ?! Because in Ecore, the containment reference specifies that B can only exist if it as an A. Therefore the multiplicity from B to A is always 1, isn’t it ?!

0..1 would mean that an instance of B can have an A or not.

UPDATE: my task is to transform the following UML diagram into Ecore

+---+ 0..1   * +---+ *     1  +---+
| A |<>--------| B |--------<>| C |
+---+          +---+          +---+

I am not sure how to map the UML composition to Ecore

  • Containment reference from A to B, upperbound: -1
  • Opposite reference B to A, lowerbound 0, upperbound 1
  • Containment reference from C to B, upperbound: -1
  • Opposite reference B to C, lowerbound = uperbound = 1

Am I right ?!

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1 Answer

  1. Editorial Team

    The meaning of your UML is that A can contain many Bs, C contains many Bs, and B can reference 0..1 As and exactly one B.

    This UML diagram is incorrect because an instance of B cannot be shared (that is the meaning of composition). So the link B-C should also be 0..1 and in that case you can use containment from both A and C.

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