Timeline for UML aggregation: how can the "whole" exist without its "parts"?
Current License: CC BY-SA 4.0
6 events
| when toggle format | what | by | license | comment | |
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| Jun 7, 2021 at 0:16 | comment | added | PerformanceDBA | @Maggyero 1) The empty set; the empty path; the NULL; etc, do not exist in reality, we can stop talking about it. It exists only in the theory, because the theory demands it, such discussion must be limited to the classroom. 2) The Whole is a Whole because it is defined as such, the definition is generic. Whether a particular instance of a Whole is filled or partially filled with parts, is different story, it does not affect the [generic] definition. | |
| Dec 13, 2020 at 1:48 | comment | added | Géry Ogam | Interesting. But is emptiness a whole (e.g. empty path, empty set, empty calendar)? And is a partial whole a whole (e.g. car without wheels)? I added a similar comment to this excellent answer. | |
| Dec 9, 2020 at 7:25 | comment | added | Christophe | @Maggyero These are interesting thoughts. But there are a lot of wholes that can actually exist without a part: an empty path, an empty set, a car without wheels (although it does not provide its full functionality), a calendar without meetings, etc. If the parts are mandatory (e.g. triangle), the multiplicity shall indicate it (minimum different from 0, in the case of the triangle 3..3). | |
| Dec 9, 2020 at 2:05 | comment | added | Géry Ogam | Very interesting Chris. "It is generally understood as a part/whole relation, with parts that can potentially be shared. This strongly suggest that the part can exist without the whole." I agree, but that does not mean that the whole can exist without the part, which was what the OP thought was also implied and confused him. To me there is no such an implication: aggregation is a part–whole relationship, meaning that the whole cannot exist without the part (not the other way round), as opposed to association which is not a part–whole relationship (cf. my answer). | |
| Dec 30, 2019 at 1:41 | comment | added | user188153 | Interestingly OMG seems to be very reluctant to actually define those terms clearly. Even for the composite aggregation there are very different interpretations of what OMG states in their specs. This is Pandora's jar for ontologists. | |
| Dec 28, 2019 at 17:51 | history | answered | Christophe | CC BY-SA 4.0 |