Simulation of Object Oriented Models using Animation

1 © NOKIA ESM 02 – 3 June 2002 – Ian Oliver, [email protected] Nokia Internal Use Only

Simulation of Object Oriented Models using Animation

Dr. Ian Oliver

Nokia Research Center

Helsinki, Finland

ESM 02 – 3 June 2002


What people understand...

• or...the eternal conflict between software engineers’ world and the rest of the worlds’ view of the world...

• For example, developing a (another) library system...

• Analyst understands

• modelling • software • programming • UML • etc, etc, etc...

• Customer understands • books • users • library policy • etc, etc, etc...


Analyst – Customer Interaction

• Analyst examines the customer’s current system and produces:

• class diagrams • sequence diagrams • business process descriptions • lots of other documentation

• Customer wants the final product

• Analyst checks that the his models are acceptable to the customer by;

• showing the analysis documentation • making presentations • building prototypes for demonstration....


The prototypes

• The customer sees this...

• and likes what he sees.....the analyst is very happy


The final product (based upon acceptance of the prototype!)

• Doesn’t quite match the customer’s expectations

• Is more expensive that thought

• Is delivered later than promised

• Functionality doesn’t work in the way the customer

wants nor the way the customer’s business works....

Why..?


Some problems...

• Prototyping takes time and skill

• Prototyping requires that someone takes the models and accurately translates them into something that the customer can understand.

• Customer may misunderstand the prototypes, for example:

• ”What a nice user-interface....it must be good!” • ”Looks fine....nice colours! Exactly what I wanted!”

• The wrong people might assess the prototype

• The prototype might just be too early....


Animation

• Animation can be consdered ”early prototyping” where the model itself is executed ... or possible ways in which a contract can be fulfilled.

• No translation to code • No misunderstandings of the requirements • No misleading user-interface issues

• But...in order to work successfully

• The customer and the analyst must work together with the

models and their animations.


Animation in Context

Proof,

Symbolic Execution Prototyping

Animation

Model based Source code based

Non-Executable

Executable


Supporting Technologies

• Object Orientation

• Unified Modelling Language

• Design-by-Contract

• Object Constraint Language


Example (start)

u1:User c1:Copy

context User::loanCopy(c:Copy)

pre: c.onShelf=TRUE

post: u.loans->existsNew(l:Loan | l.copy=c) and

c.onShelf=FALSE and c.onLoan=TRUE.

u1.loanCopy(c1)

onShelf=True

UML Object Diagram:

Action Instance

- to be ”animated” on the starting state.


Example (middle)

• The animation process

1. Check pre-condition 2. Path generation 3. Generate FSC operators 4. Apply FSC operators 5. Check post-condition 6. Check invariants 7. Present final states to the user


Example (finish)

u1:User

l1:Loan

c1:Copy

onShelf=False

onLoan=True

This model does indeed satisfy the contract’s post-condition !


Complications (1)

• Simple animations are reasonably straightforward !

• Animation in the presence of: • Incomplete specification / models • Ambiguous information • Undefinedness

• issorted?() • negation • x>0 – infinite sets • missing information

• Multiple paths • and • or


• Contract Fulfilment

• Non-Determinancy

• Ambiguous Information

Complications (2)

•Library.publications.copies->existsNew(c:Copy)

•Library.publicationc.copies->excludes(c:Copy)

•User.loans -> select(current) -> size < 5

•Library.publications.copies->isSorted?()


Complications (3)

• How complete is the model...?

• Rule of circumscription

• How do you cross a river?

• If the animation talks about things that are not present in the model then the starting state is not complete enough


Complications (4)

• Multiple Paths through Post-Condition

( a=1 and b=2 ) or c=3

• a = 1 ; b = 2 ; c = 3

• b = 2 ; a = 1 ; c = 3

• c = 3

• a = 1 ; b = 2

• b = 2 ; a = 1

• c = 3 ; a = 1 ; b = 2

• c = 3 ; b = 2 ; a = 1


Heuristics

• Minimum Obligation • includes • excludes • existential quantification • caridinality constriants, eg: size

• Least Interference • model sorting • default ordering


Towards Simulation...

• Systems don’t just use simple, single operations and simple easy contract specifications unfortunately

• What would happen if... 1. a user loans a book 2. then another user 3. then another user 4. then a book is reserved 5. then another book is reserved 6. a user returns a book 7. a user leaves 8. etc...etc...

• Filmstrips can be used to help visualise this....


Filmstrips

Time...

a()

b()

b()

c()

c()

c()

What are the possible outcomes if a(), b() and then c() are run on this starting state?


Proof, Symbolic Execution, Animation and Prototyping

• Proof • can tell us whether a system is consistent, complete

(maybe) • is horribly mathematical

• Symbolic execution • can tell us how a system may look like given certain

constraints • is again too mathematical

• Animation • can visualise particular actions for given states • is limited to particular well chosen cases

• Prototyping • can help visualise the software • can be misunderstood and is quite far removed from the

actual model itself (user-interface syndrome)


Other Applications

• Acceptance Testing

• Customer can check whether the model does what the customer wants

• Validation of customer requirements

and • Validation of analyst’s interpretation

• As animation is better suited to particular critical cases then these cases become a set of tests to be applied throughout the development process.


Conclusions

• Not a ”silver bullet”

• Not too mathematical – UML/OCL is ”more readable”

• Brings customer and analyst closer together

• Avoids ”user-interface syndrome”

• Works at the model level early in the development process

• Very good at resolving certain critical issues with regard to the functionality required in the system

• Doesn’t need tool support – works with pen and paper

• Good for teaching design-by-contract principles and rigorous or formal modelling techniques

• Cheap(er)


The End

Dr. Ian Oliver

Nokia Research Center

Helsinki

Finland

[email protected]

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Simulation of Object Oriented Models using Animation