Presentation given at VAO 2014 in York

1. Towards Constraint-Based Model Types:
A Generalised
Formal Foundation for Model Genericity
Steffen Zschaler
22 July 2014
VAO, York

2. Towards Constraint-Based Model Types:
A Generalised
Formal Foundation for Model Genericity
Steffen Zschaler
22 July 2014
VAO, York

3. Reuse in model management
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Model transformation specifications
Untyped
• No documentation
of assumptions
• No checking of
applicability for a
given model
Typed over one
specific meta-model
• Only work for models
that instantiate the
particular meta-model
• Need to rewrite
transformation from
scratch for any
similar meta-model.

4. Reuse in model management
22/07/2014 2
Model transformation specifications
Untyped
• No documentation
of assumptions
• No checking of
applicability for a
given model
Typed over one
specific meta-model
• Only work for models
that instantiate the
particular meta-model
• Need to rewrite
transformation from
scratch for any
similar meta-model.
We need a type system that is both sufficiently lax and
sufficiently precise to capture the best of both worlds.
(NB Can think of such model types as views on the
models to be manipulated.)

5. Existing approaches
• Two attempts at such type systems
exist:
– Model Typing (Steel, Guy, Combemale, et al.)
– Model Concepts (de Lara, Guerra, Rose, et
al.)
• All have problems
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6. Example problems
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mmo NewSM (s : Simple) {
s += new StateMachine ()
}

7. Example problems
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mmo NewSM (s : Simple) {
s += new StateMachine ()
}
StateMachine
State
name: String
Transition
event: String
initialState
0..1
containedState *
src
1
tgt
1
incoming
*
*
outgoing
Difference between Simple and Mandatory-startMandatory-start <:Steel Simple

8. Example problems
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mmo NewSM (s : Simple) {
s += new StateMachine ()
}
StateMachine
State
name: String
Transition
event: String
initialState
0..1
containedState *
src
1
tgt
1
incoming
*
*
outgoing
Difference between Simple and Mandatory-start
Error: Allows passing in
Mandatory-start instance, but breaks it.
Mandatory-start <:Steel Simple

9. mmo NewSM (s : Mandatory-start) {
sm := new StateMachine () ;
sm.initialState += new State () ;
s += sm
}
Example problems
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StateMachine
State
name: String
Transition
event: String
initialState
0..1
containedState *
src
1
tgt
1
incoming
*
*
outgoing
Difference between Simple and Mandatory-startMandatory-start <:Guy Simple

10. mmo NewSM (s : Mandatory-start) {
sm := new StateMachine () ;
sm.initialState += new State () ;
s += sm
}
Example problems
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StateMachine
State
name: String
Transition
event: String
initialState
0..1
containedState *
src
1
tgt
1
incoming
*
*
outgoing
Difference between Simple and Mandatory-start
Over-restriction: Would work with any
Simple instance, but cannot specify.
Mandatory-start <:Guy Simple

11. Two general problems
1. Focus on external contracts
– Can validate invocations but not
implementations
2. No formal definition
– Cannot analyse correctness
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12. Towards a solution
1. Provide a formalisation
– Explicit type system for model types
– Explicitly include constraints on the structure
of acceptable models
2. Define a notion of an internal contract
– In the paper defined through a set of type
inference rules
– Key really: Dataflow analysis of MMO
implementation
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13. Example
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See paper for type rules

14. Example
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See paper for type rules

15. Example
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Statements typed by
their effect on
system states
data flow analysis
States assign model types
to variables (see paper)
See paper for type rules

16. Example
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See paper for type rules

17. Example
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Append rule generates
additional constraints.
Here: Forbids mandatory
associations from StateMachine.
See paper for type rules

18. Example
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See paper for type rules

19. Example
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See paper for type rules

20. Example
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See paper for type rules

21. Example
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See paper for type rules

22. Conclusions and Outlook
• Need better understanding of generic
model types
– Internal contracts
– Constraint-based model types may provide
the basis
• Proper formalisation needed
• Limits of data-flow analysis?
22/07/2014 8

23. QUESTIONS?
Steffen Zschaler
szschaler@acm.org, @szschaler
22/07/2014 9