The document discusses a framework for utilizing the visitor pattern in domain-specific languages (DSLs) to automate model transformations in software development. It highlights the advantages and disadvantages of the visitor pattern and presents a visitor generation framework (VGF) designed to enhance model behavior evolution efficiently. The conclusions emphasize the VGF's ability to mitigate challenges associated with evolving DSL structures and behaviors.

1. Automatic Application of
Visitors to Evolving
Domain-Specific
Languages
Computer Science Department
University of York1
& Willink Transformations Ltd2.
Adolfo Sánchez-Barbudo Herrera1, Ed Willink2, Richard Paige1, Louis Rose1, Dimitris Kolovos1
(asbh500@york.ac.uk ed@willink.me.uk richard.paige@york.ac.uk, louis.rose@york.ac.uk, dimitris.kolovos@york.ac.uk)

2. 2
Agenda
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Introduction to Modeling (MDSD, MDE,...)
Model Behaviour
Model Evolution
Visitor Pattern
Visitor Generation Framework (VGF)
VGF for Model Behaviour Evolution
Conclusions

3. 3
Modeling Introduction
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Models as main artefact for developing SW
Models as abstract representations of SW
Higher level of abstraction than programs
Programs replaced by Models
uBlog DSL

4. 4
Modeling Introduction II
With a modeling language you can create model
instances, which correspond to objects at runtime.

5. 5
Modeling Introduction III
● MDE techniques to support software
development:
Model to Text
Model to Model
Transformations
Transformations

6. 6
Model Behaviour
● Model concepts may comprise behaviour
● Usually modelled as Operations
A user can create new posts in a given uBlog

7. 7
Model Evolution
● Model evolution - like SW evolution - is a
recurrent and open issue.

8. 8
Model Evolution II
● Same issues regarding behaviour.

9. 9
Visitor Pattern
● OOP design pattern
○ Well known solutions to a recurring problem
● Separate structure from behaviour

10. 10
Visitor Pattern II
● Main advantage
○ Add/Remove/Modify/Replace behaviour without
changing structure.
○ Ideal when working with third party structures.

11. 11
Visitor Pattern III
● Main disadvantage
○ It’s not the ideal pattern with evolving structures.

12. 12
Visitor Pattern IV
● Visitors applied to modeling languages

13. 13
Visitor Generation Framework
● MDE based prototype to automatically apply
the visitor pattern.
● Part 1.
○ Setup the DSL to apply the visitor pattern
○ via a M2M Transformation.
● Part 2.
○ Generate DSL-specific visitors framework
○ via M2T Transformations.

14. 14
Visitor Generation Framework II
● M2M transformation to prepare the DSL

15. 15
Visitor Generation Framework III
● DSL-specific visitors framework generation
1. Visitor/Visitable
Interfaces
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2. Default Abstract
Implementations
Contextful Visitor
Null Visitor
Extending Visitor
Delegating Visitor
...

16. 16
Visitor Generation Framework IV
● VGF abstract visitors examples:

17. 17
Visitor Generation Framework V
● VGF Overview
Visitable
DSL
Implementation
DSL
Model
VGF
DSL-Specific Visitors
Framework
Visitor/
Visitable
Interfaces
Manual
Generated
Abstract
Visitors
Impl.
More
MDE-based
generators
Generated
Visitors
Manual
Visitors

18. 18
VGF for models behaviour evolution
● Evolving behaviour - Same structure
Behaviour
No Model Visitors
Model Visitors
VGF
Adding
Changes DSL
Ok
Ok
Removing
Breaks clients
Breaks clients
Breaks clients
Modifying
Changes DSL
Ok
Ok
● Evolving structure - Same behaviour
Structure
No Model Visitors
Model Visitors
VGF
Adding
Ok
Breaks visitors
Ok
Removing
Breaks clients
Breaks clients
Breaks clients
Modifying
Ok
Ok
Ok
Convenient
Inconvenient
Very Inconvenient

19. 19
Conclusions
● VGF:
○ Automatically brings the benefits of the visitor
pattern to DSLs
○ Automatically creates a DSL-specific framework to
leverage visitors creation
○ It´s a convenient practice when a DSL has unclear
behaviour or an evolving one
○ It may mitigate the drawbacks of the visitor pattern
with respect to language structure evolution

20. Thank you very much
Questions ?
doubts, feedback, enquiries, etc. to asbh500@york.ac.uk