This document discusses the importance of modeling opposites in relationships between classes. It explains that in OCL, every class-typed property has an opposite property defined. Modeling opposites explicitly supports efficient transformation modeling. For example, modeling the opposites in a QVT relation allows Eclipse QVT relations to run 30 times faster than comparable ATL transformations and with linear rather than quadratic performance scaling.

1. Made available under EPL 1.0
The Importance of Opposites
Edward D. Willink
Willink Transformations Ltd
Eclipse Foundation
MMT Component co-Lead
OCL Project Lead
QVTd Project Lead
QVTo Committer
OMG (Model Driven Solutions)
OCL 2.3, 2.4, 2.5 RTF Chair
QVT 1.2, 1.3, 1.4 RTF Chair
OCL 2016 @ MODELS 2016
2nd October 2016

2. 2-October-2016 Opposites 2Made available under EPL 1.0
Bidirectional Navigation Relationships
Arbitary navigation
context Parent
inv: children->forAll(parent = self)
context Child
inv: parent.children->includes(self)

3. 2-October-2016 Opposites 3Made available under EPL 1.0
Unidirectional Navigation Relationships
No opposite
let aParent:Parent = ... in aParent.children->size()
run-time optimization
no wasted memory supporting the opposite
analysis inconvenience
evolution necessity
Child is part of a pre-existing immutable metamodel
Parent is part of a new metamodel

4. 2-October-2016 Opposites 4Made available under EPL 1.0
Implicit Navigation Relationships
Implicit opposite - use the target class name
let aChild:Child = ... in aChild.Parent <> null implies ...
may be ambiguous - multiple roles
Disambiguated Implicit opposite
- use the target class name qualified by property
let aChild:Child = ... in aChild.Parent[children] <> null
implies ...
Every Class-typed Property has an opposite

5. 2-October-2016 Opposites 5Made available under EPL 1.0
Modeling an ATL Rule
resolveTemp

6. 2-October-2016 Opposites 6Made available under EPL 1.0
Modeling the
QVTc mapping
for a QVTr relation

7. 2-October-2016 Opposites 7Made available under EPL 1.0
Full opposites
OCL defines an opposite role name
MOF supports it via a Tag
Ecore supports it via an EAnnotation
Is the opposite a Set?
inference:
container is 0..1
non-container can be anything => Bag
QVTc trace is nearly always 1..1
need opposite upper/lower/unique/ordered
Eclipse QVTd uses further EAnnotations
UML 2.5's embedded OCL needs further Tags

8. 2-October-2016 Opposites 8Made available under EPL 1.0
Summary
Every Class-typed Property has an opposite in OCL
Supports efficient transformation modeling
EXE 2016 paper :
Thirty fold speed-up of Eclipse QVTr wrt ATL
Linear performance for Eclipse QVTr wrt quadratic ATL