OCL Visualization A Reality Check
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1) The document discusses various approaches to visualizing OCL constraints, including traditional AST visualization, vOCL, Eclipse QVTs visualization, constraint diagrams, and Visual OCL. 2) It analyzes examples of each approach using a sample OCL constraint and finds that constraint diagrams can represent constraints compactly but are only partially expressive. Eclipse QVTs visualization and traditional AST are more complete but more verbose. 3) The author concludes that while pictures can complement text for understanding constraints, text will generally be better for expressing complex OCL expressions and tooling support for visual editors is unlikely. Debugging aids like AST and QVTs visualizations can still be helpful.
![16-September-2019 OCL Visualization - A Reality Check 13Made available under EPL 2.0
Running Example using Eclipse QVTs
Rectangles
=> class instances
Rounded rectangles
=> DataType values
Ellipses
=> OCL operations
edges have <<roles>>
Solid edges
=> unit value matching
Dashed edges
=> [0..*] values matching
11 nodes and 15 edges](https://image.slidesharecdn.com/oclvisualization-slides-190916194341/85/OCL-Visualization-A-Reality-Check-13-320.jpg)
OCL Visualization A Reality Check
- 1. Made available under EPL 2.0 OCL Visualization A Reality Check Edward 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 2019 @ MODELS 2019 16th September 2019
- 2. 16-September-2019 OCL Visualization - A Reality Check 2Made available under EPL 2.0 Overview Background Traditional AST visualization vOCL 2018 problems Fixed vOCL Eclipse QVTs visualization Constraint Diagram Visual OCL Summary / Conclusion
- 3. 16-September-2019 OCL Visualization - A Reality Check 3Made available under EPL 2.0 Background Text can be good Pictures can be good Text can be better Pictures can be better Text dominant for expressions (except SDL) UML graphical – why no graphical OCL ? OCL 2018 => vOCL paper worth discussion reviewer's / audience criticisms not rebutted
- 4. 16-September-2019 OCL Visualization - A Reality Check 4Made available under EPL 2.0 Running Example Example constraint context Hospital inv uniquePatientId: self.patients->forAll(p1, p2 | p1 <> p2 implies p1.id <> p2.id) Equivalent to context Hospital inv uniquePatientId: self.patients->isUnique(id)
- 5. 16-September-2019 OCL Visualization - A Reality Check 5Made available under EPL 2.0 Traditional AST Visualization UML-like solid containment dashed references 18 nodes, 22 edges
- 6. 16-September-2019 OCL Visualization - A Reality Check 6Made available under EPL 2.0 vOCL Traditional AST is instance-based instances of OCL metamodel requires knowledge of OCL internals references by name to user metamodel vOCL is class-based re-uses user metamodel to define variables mnemonic icons for common OCL operations vOCL constraint is a doodle on the class diagram new doodling semantics
- 7. 16-September-2019 OCL Visualization - A Reality Check 7Made available under EPL 2.0 vOCL example from 2018 paper blob is the self instance of the not-grayed class ellipses use Class-typed reference properties rounded rectangles use DataType properties additional icons for OCL operations arrows denote 'reading order' vague semantics
- 8. 16-September-2019 OCL Visualization - A Reality Check 8Made available under EPL 2.0 AST visualization of vOCL example green reading order markup blob - self - ok ....patients - ok ....size() - ok ....<= - lhs ok <= ... - rhs inverted pragmatic self.beds backwards
- 9. 16-September-2019 OCL Visualization - A Reality Check 9Made available under EPL 2.0 Fixed vOCL example Multiple paths for multiple instances/evaluations Blob now starts two paths black path as in original paper to read the LHS self.patients.size() <= new green path to read the RHS self.beds >= both paths read towards the binary <= operation
- 10. 16-September-2019 OCL Visualization - A Reality Check 10Made available under EPL 2.0 AST visualization of fixed vOCL example two blobs two bottom-up paths 'reading order' is now AST evaluation blob defines 'self' value edge passes value node computes value
- 11. 16-September-2019 OCL Visualization - A Reality Check 11Made available under EPL 2.0 Running example using Fixed vOCL Blobs identify three variables starting five paths self.patients self.patients.id <> implies self.patients.id <> implies self.patients <> implies self.patients <> implies Nested rounded rectangles for multiple uses 9 nodes + 12 edges (AST: 18 nodes, 22 edges)
- 12. 16-September-2019 OCL Visualization - A Reality Check 12Made available under EPL 2.0 Eclipse QVTs OCL visualization AST visualization Object Diagram: instances of OCL metamodel vOCL Class Diagram: doodle on user metamodel Eclipse QVTs patterns Object Diagram: instances of user metamodel auto-generated debug aid for matching schedule example embedded in QVTr
- 13. 16-September-2019 OCL Visualization - A Reality Check 13Made available under EPL 2.0 Running Example using Eclipse QVTs Rectangles => class instances Rounded rectangles => DataType values Ellipses => OCL operations edges have <<roles>> Solid edges => unit value matching Dashed edges => [0..*] values matching 11 nodes and 15 edges
- 14. 16-September-2019 OCL Visualization - A Reality Check 14Made available under EPL 2.0 Constraint Diagrams Stuart Kent, OOPSLA 1997 Constraint Diagrams: Visualizing Invariants in Object-Oriented Models. Visual Set membership blobs for members shapes for types blobs within shapes for membership edges for relationships ... Venn Diagrams Not OCL related concepts ... better perspective
- 15. 16-September-2019 OCL Visualization - A Reality Check 15Made available under EPL 2.0 Running example - Constraint Diagram Ellipses - user metamodel types Blobs - distinct instances typed by background Edges - metamodel relationships Powerful set concepts align well to OCL some OCL concepts hard to represent 8 nodes, 4 edges
- 16. 16-September-2019 OCL Visualization - A Reality Check 16Made available under EPL 2.0 Visual OCL Christiane Kiesner, Gabriele Taentzer, Jessica Winkelmann TU Berlin Technical Report 2002/23 Visual OCL: A Visualization of the Object Constraint Language A new 'UML' diagram re-uses statechart idioms hierachy of decorated compartments
- 17. 16-September-2019 OCL Visualization - A Reality Check 17Made available under EPL 2.0 Running Example - Visual OCL ? Draw as: 12 nodes / compartments 3 edges 10 text tokens
- 18. 16-September-2019 OCL Visualization - A Reality Check 18Made available under EPL 2.0 Summary / Comparison Naive AST - verbose, uses OCL metamodel vOCL - user-friendly, may become cluttered QVTs - patterns, variables avoid clutter Constraint Diagram - can be very good beware: running example hits a 'sweet spot' Visual OCL - adequate
- 19. 16-September-2019 OCL Visualization - A Reality Check 19Made available under EPL 2.0 Summary / Reality Text can be better, Pictures can be better Text dominant for expressions Complex expressions need the 'best' exposition patterns Text tooling unavoidable - ASCII compatibility Visual tooling specialized - UMLDI is a 'future' AST / QVTs visualization - a helpful debug aid Other Visual OCL editors unlikely to happen
- 20. 16-September-2019 OCL Visualization - A Reality Check 20Made available under EPL 2.0 Future Work ? Eclipse QVTs - adequate, complete node => metamodel instance / operation edge => metamodel relationship / operation role Constraint Diagram - compact, partial node => metamodel instance edge => metamodel relationship background => set membership / typing ?? Merge the two ?? ?? Questions ??