A Manifesto for Semantic Model Differencing

Transcription

1 A Manifesto for Semantic Model Differencing ME-10, October 2010 Shahar Maoz, Jan Oliver Ringert, Bernhard Rumpe Lehrstuhl Informatik 3 ()

2 Seite 2 One slide abstract Existing approaches to model differencing concentrate on heuristics matching between model elements and on finding and presenting differences at a concrete or abstract syntactic level. While showing some success these approaches are limited to comparing syntactic structures. We present our vision to develop semantic diff operators for model comparisons: operators whose input consists of two models and whose output is a set of diff witnesses, instances of one model that are not instances of the other. We demonstrate our vision using two concrete diff operators for class diagrams and activity diagrams, with motivating examples, formal definitions, and early prototype implementations. Discuss new challenges emerging from the vision

3 Seite 3 Motivating example 1 cd1.v1 cd1.v2 1 Employee manages * * Task 0..2 Task sdate: Date sdate: Date 1 managedby manages managedby Manager Employee 0..1 * 0..1 Manager What is the semantic difference between cd1.v1 and cd1.v2?

4 Seite 4 Motivating example 1 cd1.v1 cd1.v2 1 Employee manages * * Task sdate: Date managedby Manager Employee Task 0..2 sdate: Date manages managedby Manager * 0..1 om 1 t1:task sdate = date1 t2:task sdate = date2 om 1 2 diff(cd1.v1,cd1.v2) manages om 2 :Employee t3:task sdate = date3 :Manager :Manager managedby om 2 2 diff(cd1.v2,cd1.v1)

5 Seite 5 Motivating example 2 cd2.v1 cd2.v2 <<singleton>> Department worksin has * Employee Department worksin has * Employee What is the semantic difference between cd2.v1 and cd2.v2?

6 Seite 6 Motivating example 2 cd2.v1 cd2.v2 <<singleton>> Department worksin has * Employee Department worksin has * Employee om 3 d1:department {om 3, om 4 } ½ diff(cd2.v2,cd2.v1) d2:department om 4 :Employee

7 Seite 7 Motivating example 3 cd3.v1 <<abstract>> Person 1 cd3.v2 Employee livesin 1 1 Address Employee 1 livesin Address What is the semantic difference between cd3.v1 and cd3.v2?

8 Seite 8 Motivating example 3 cd3.v1 <<abstract>> Person 1 cd3.v2 Employee livesin 1 1 Address Employee 1 livesin Address No difference. cd3.v1 and cd3.v2 have equal semantics!

9 Seite 9 Motivating example 4 register ad.v1 register ad.v2 external external internal internal get welcome pack get welcome pack add to website assign keys add to website manager interview manager report manager interview manager report authorize payment authorize payment What is the semantic difference between ad.v1 and ad.v2?

10 Seite 10 Motivating example 4 register 1 ad.v1 register ad.v2 external external internal get welcome pack 2 internal get welcome pack 4 add to website 3 assign keys add to website manager interview manager report 5 manager interview manager report authorize payment authorize payment Example diff witness for internal employees: the trace <register>, <get welcome pack>, <>, <add to website>, <manager interview> was possible in ad.v1 and is no longer possible in ad.v2. No diff witnesses for external employees.

11 Seite 11 Motivating example 5 register ad.v3 register ad.v4 external external internal internal get welcome pack get welcome pack assign keys add to website assign keys add to website manager interview manager interview manager report manager report authorize payment authorize payment What is the semantic difference between ad.v3 and ad.v4?

12 Seite 12 Motivating example 5 register 1 ad.v3 register ad.v4 external external internal get welcome pack 2 internal get welcome pack assign keys add to website assign keys add to website manager interview manager interview manager report authorize payment 3 manager report authorize payment Example diff witness for external employees: the trace <register>, <>, <authorize payment> was possible in ad.v3 and is no longer possible in ad.v4. No diff witnesses for internal employees.

13 Seite 13 Formal definitions Modeling language ML = <Syn,Sem,sem> [HR04] Syn: set of syntactically correct expressions Sem: semantic domain sem: semantic mapping sem: Syn! (Sem) We define the generic semantic diff operator diff : Syn Syn! (Sem) diff(e 1,e 2 ) = { s Sem s sem(e 1 ) s sem(e 2 ) } Members of the set diff are called diff witnesses

14 Seite 14 Features of diff Semantics-based (agnostic to syntax) Constructive (generates witnesses) State-based (agnostic to edit operations) diff is not symmetric diff(e 1,e 1 )= ; diff(e 1,e 2 ) Å diff(e 2,e 1 ) = ;

15 Seite 15 Concrete diff operator for class diagrams We use the class diagrams of UML/P [Rum04] Syntax defined using MontiCore [KRV08] Semantics given as a set of finite object models [EFLR98] We use a complete semantics: whatever is not specified in the CD is indeed not present in the object models Supported features: generalizations (inheritance), abstract and singleton classes, class attributes, unidirectional and bidirectional associations with multiplicities, enumerations, aggregation, and composition.

16 Seite 16 cddiff: Semantic diff for CDs We define a specialization of diff for CDs cddiff k is a family of bounded operators For all k >= 0, cddiff k (cd 1,cd 2 ) = { om OM om cddiff(cd 1,cd 2 ) om < k +1 )} where om is the maximal number of instances per class in om. We give a bounded definition since the unbounded operator might not be computable

17 Seite 17 Concrete diff operator for activity diagrams We use Eclipse UML2 activity diagrams Alternative syntax defined using MontiCore Semantics given as a set of traces In our AD language we allow a single initial node but many initial states defined by the values of input variables We support external non-determinism by input variables, and internal non-determinism by interleaving semantics of forked branches (guarded transitions have to be disjoint) Supported features: input variables, local variables, fork, join, decision, merge, assignments to local variables from action nodes, guarded transitions from decision nodes

18 Seite 18 addiff: Semantic diff for ADs We define a specialization of diff for ADs Looking only for the shortest diff traces Formal definition: addiff(ad 1, ad 2 ) = { tr tr 2 sem(ad 1 ) Æ tr sem(ad 2 ) tr': tr' 2 sem(ad 1 ) Æ tr' sem(ad 2 ) Æ tr' v tr } We compute only one diff witness for each set of input values (i.e., for each initial state)

19 Seite 19 Implementation and evaluation We have implemented prototypes for bounded cddiff, using Alloy [Jac06] for addiff, using a translation to SMV (and JTLV [PSZ10]) Prototypes integrated into Eclipse plug-ins for CDs using MontiCore UML/P for ADs using Eclipse UML2 framework

20 Seite 20 CDDiff prototype example screenshot screenshot

21 Seite 21 ADDiff prototype example screenshot screenshot

22 Seite 22 Challenges Computation Presentation Integration with syntactic diff

23 Seite 23 Computation challenges Computing diff witnesses may not be algorithmically easy and sometimes even impossible. When computable, its complexity depends on the specific modeling language semantics at hand. For example CDDiff must be bounded to be tractable ADDiff requires a traversal of the state space of the ADs at hand. The state space may be exponential in the size of the AD. To scale, should adapt algorithms and heuristics from formal verification (model checking), e.g., partial order reduction, abstraction / refinement etc.

24 Seite 24 Presentation challenges To be useful, diff witnesses must be presented textually or visually to the engineer. Just like for computation, the presentation of diff witnesses is language specific; it depends on the specific modeling language of the models involved and its semantics. For example For CDDiff, diff witnesses presented as object diagrams For ADDiff, diff witnesses presented visually by coloring and numbering the nodes participating in the diff trace on both ADs As there may be (possibly infinitely) many diff witnesses, it is necessary to define sorting and filtering mechanisms, to select the `most interesting' witnesses for presentation and efficiently iterate over them at the user's request.

25 Seite 25 Integration with syntactic diff As many works have suggested various syntactic approaches to model differencing, it may be useful to combine syntactic differencing with semantic differencing. For example Extend the applicability of semantic diffing in comparing models whose elements have been renamed or moved in the course of evolution, by applying a syntactic matching before running a semantic diffing: this would result in a mapping plus a set of diff witnesses. Use information extracted from syntactic diffing as a means to localize and improve the performance of semantic diffing computations.

26 Seite 26 Related work Much work on model comparison (e.g. [AP03,OWK03,MGH05, EPK06,XS07,KGE09]) Most works go beyond the concrete textual or visual representation and have defined the comparison at the abstract-syntax level, detecting additions, removals, and shifts operations on model elements To the best of our knowledge, none considers model comparisons at the level of the semantic domain [JL94] presented a tool that summarizes the semantic diff between two procedures in terms of observable input-output behaviors [PDE+08] suggested to compute a behavioral characterization of a program change using a technique called differential symbolic execution We concentrate on models, not programs; our technique is different; but our work is indeed similar in spirit to these two works

27 Seite 27 Conclusion We presented our vision on semantic diff operators for model comparison, as new fundamental building blocks for change management in model-driven engineering. We motivated our vision with examples, and gave a brief overview of the formal background and the algorithms used in our prototype implementations. Finally, we listed new research challenges that emerge from our vision, related to the computation and presentation of semantic model differences and to its integration with syntactic diffing.

28 Seite 28 Thank you!