Please explain me, what {optional} means in ship description.
Is it some value from UML documentation or a mistake?
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Geert Bellekens
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J. Doe
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Are your sure of {optional} ? I looked to the specification, i did not find it ... – granier Jan 02 '18 at 16:31
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I too, but I did not find this word on my diagram again. – J. Doe Jan 02 '18 at 16:41
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Which CASE Tools do you use? – Gholamali Irani Jan 02 '18 at 19:30
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Maybe (only maybe) it is only a mistake and class designer set the type of attribute to `Ship {optional}`. In this case the diagram shows like yours. – Gholamali Irani Jan 02 '18 at 19:48
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This is a part of diagram for a test assignment sent by me to the employer for admission to courses, so I do not know what he used to create a chart and whether it was done correctly. – J. Doe Jan 03 '18 at 18:33
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I think (!) this is an invention of StarUML (since I suppose you used this tool to create it). UML does not have such a property modifier (see p. 111 of the UML specs for a complete list of valid keywords). Optionality is represented by adding a multiplicity [0..1] like this:
However, I guess everyone could easily recognize the same semantic from that {optional} property modifier.
qwerty_so
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@granier I fostered the specs and there's nothing in that direction. Where did you see that? – qwerty_so Jan 02 '18 at 16:34
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"A lower bound of zero means the Parameter is optional" section 9.4.3.4. for Feature and Operation inherits of Feature ... – granier Jan 02 '18 at 16:38
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@Kilian i am not sure to understand what you mean by "that property above does not exist" which one ? What i cited is for Feature ... For property, for me, {optional} does not exist in the specification. – granier Jan 02 '18 at 17:04
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Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/162363/discussion-between-granier-and-thomas-kilian). – granier Jan 02 '18 at 17:08
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I looked quickly to OCL specification, since text between parenthesis should be constraint. I did not find anything about a an optional keyword. – granier Jan 04 '18 at 09:53
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See p. 111 of the specs: property modifiers are also enclosed in curly brackets. – qwerty_so Jan 04 '18 at 12:19
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yes these modifiers may be seen as constraint, the last one is a constraint :
::= ‘readOnly’ | ‘union’ | ‘subsets’ – granier Jan 04 '18 at 12:50| ‘redefines’ | ‘ordered’ | ‘unordered’ | ‘unique’ | ‘nonunique’ | ‘seq’ | ‘sequence’ | ‘id’ | . But anyway optional is neither defined as constraint in the specification nor in OCL specifiation. Or I miss something, which is possible.