1 Contractual Consistency Between BON Static and Dynamic Diagrams Ali Taleghani July 30, 2004

2 Overview Model-Driven Development & Models Contractual Consistency – The Problem Previous Work Current Work – Semantics of Dynamic Diagrams BON Development Tool – BDT Contribution and Future Work

3 MDD & Models Model-Driven Development proposes development based on models Several views can be used to describe system Models must be executable, and views consistent Contributions  Automated consistency checking  Symbolic model execution

4 Contractual Consistency – Example SD contains contracts only – No implementation Want to create account and withdraw $200 make sets (balance = 0), but precondition of withdraw requires (balance >= 200)  Contract Violation

5 Contractual Consistency SD and DD are the two views involved SD contains contracts only – no implementation Contracts are pre, postconditions and class invariants Views contractually consistent if messages in DD corresponding to routines in SD can be executed without contract violations

6 Previous Work Problem of consistency with contracts not extensively discussed –informal approaches only [Paige 2002] first to formalize problem Cites 4 criteria for checking consistency Last criteria is contractual consistency We add additional constraints for implementation

7 Semantics of Dynamic Diagram Message m i in DD is mapped to a feature r i in the target class in SD Routine takes system from one system state constraint (SSC i ) to the next (SSC i+1 ) SSC represents a constraint on the attributes in the system SSC i+1 constructed using SSC i and contracts of r i

8 Current Contribution - 1 Check Contractual Consistency using Symbolic Model Execution Define Symbolic Execution Step as execution of one message in DD successful iff Precondition of routine is satisfied SSC is not a contradiction

9 Current Contribution - 2 Views contractually consistent iff No implementation provided Require use of Theorem Prover Use Simplify from ESC/Java Automatic and Fast Returns counter example

10 BON Development Tool - BDT Static Diagramming Tool Construct Class diagrams Include contracts

11 BON Development Tool - BDT Dynamic Diagramming Tool Draw objects and messages Assign messages to routines from SD

12 BON Development Tool - BDT Consistency Tool Specify an initial state constraint Contract violation results in counter example User can use counter example to make changes to contracts, messages

13 Comparison to Tool of [Gao2004] Gao’s Tool  Test drivers and implementation required  Checks one or a few execution paths  Complete (for that execution) BDT  Automatic and no implementation required  All execution paths starting in a state constraint are checked  Incomplete since working with a theorem prover

14 Contribution First contractual consistency tool without the need to specify implementation Early symbolic execution of partial models Can use dynamic (collaboration) diagrams Use contracts only – higher level than MDD State Chart Action Languages Tool is user friendly  Simplify works automatically under the hood  Simplify works quickly

15 Future Work Work out theory for sub-messages in DD BDT  Add invariants and inheritance  Support quantifications  Combine BDT with EDT for complete code generation  Add support for program verification – using ERC

16 Thank You