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OCL syntax on association ends [message #1862623]

Fri, 15 December 2023 08:47

Nathan Duchesne

Messages: 1
Registered: December 2023

Junior Member

Hello

Suppose I have the following data model:
entity Person {
String name
Set(Book) editor oppositeTo editedBy
Set(Chapter) chapterAuthor oppositeTo author
Set(Book) bookAuthor oppositeTo author
}
entity Book {
String title
Set(Person) editedBy oppositeTo editor
Set(Chapter) chapters oppositeTo book
Set(Person) author oppositeTo bookAuthor
Set(Publisher) publisher oppositeTo publish
}
entity Chapter {
String title
String text
Set(Person) author oppositeTo chapterAuthor
Set(Book) book oppositeTo chapters }
entity Publisher {
String name
Set(Book) publish oppositeTo publisher
}
enum Role {
USER
}

and I want to construct an OCL constraint such as "A user u can associate a Book b with a Publisher p if and only if all the authors and editors of b have already authored at least three chapters in books published by p."

Obviously one way of doing so in
Book is using collect and flatten:
add(publisher) constrainedBy [
self.author->union(self.editedBy)->forAll(x |
target.publish
->collect(y | y.chapters)
->flatten()
->select(c |
c.author->includes(x)
)->size() >= 3
)
]
and by defining the constraint on the opposite entity as well (in this case, Publisher).

Now comes my question: Is the above query equivalent to:
self.author->union(self.editedBy)->forAll(x |
target.publish.chapters
->select(c |
c.author->includes(x)
)->size() >= 3
)

i.e can I link multiple Set associations and will this flatten out the result into one Set, or will this give me a Set of Sets, hence both queries not being equivalent?

Thank you guys for your time and don't hesitate if you need any more specifications!

Nate

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Re: OCL syntax on association ends [message #1862637 is a reply to message #1862623]

Sat, 16 December 2023 16:27

Ed Willink

Messages: 7655
Registered: July 2009

Senior Member

(Your use of target rather than x is presumably a typo.)

OCL evolved for use with UML whose multiplicities become collections. There are no nested multiplicities consequently OCL was defined to always flatten nested collections. This design mistake was mitigated/confused by the addition of collectNested and flatten.

In your example the eager flattening should indeed make the expressions equivalent.

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