![Library Source Codeclass Library { Vector<Reader> readers; Vector<Book> books;Hashtable<Reader,Book[]> borrows;intnextReaderId; public void handle(Messagem) {switch(m.id) {case REGISTER:register(m);break;case ADD_BOOK:add_book(m);break;case BORROW:borrow(m);break; ...} } ...}application stateentry pointinterface](https://image.slidesharecdn.com/reverseengineeringandtheorybuildingv3-110806065205-phpapp02/85/Reverse-engineering-and-theory-building-v3-17-320.jpg)
![Borrowingpublic voidborrow(Messagem) {int id = (int)m.getData(0); String name = (String)m.getData(1); Reader reader = getReader(id); Book book = removeBook(name); Book[] borrowed = borrows.get(id);if(borrowed.length < BORROW_LIMIT) { Book[] updated = new Book[borrowed.length+1];Array.copyInto(borrowed,updated);updated[borrowed.length] = book;borrows.put(reader,updated);m.reply(OK); } else m.reply(FAIL);}data accessdata access](https://image.slidesharecdn.com/reverseengineeringandtheorybuildingv3-110806065205-phpapp02/85/Reverse-engineering-and-theory-building-v3-19-320.jpg)
![Partial Theories are Defined by Rulesr = (Reader)[name = n; id = i]not(R->includes(r))---------------------------------------------- [EvalRule] (Eval)[ data = (AddReader)[name = n]; result = (ReaderAllocated)[id = i]; change = (StateChange)[ pre = (Library)[ readers = R; books = B; borrows = X; nextReaderId = i]; post = (Library)[ readers = R->including(r); books = B; borrows = X;nextReaderId = i+1 ] ] ]](https://image.slidesharecdn.com/reverseengineeringandtheorybuildingv3-110806065205-phpapp02/85/Reverse-engineering-and-theory-building-v3-24-320.jpg)
![Evaluating More than one Data Access(Evals)[accesses = Seq{}; changes = Seq{}; results = R] (EvalsRule) (Eval)[data = a; change = c; result = r]--------------------------------------------------------- (EvalsRule)(Evals)[accesses = Seq{a}; changes = Seq{c}; results = Seq{r}] (Evals)[accesses = P; changes = C; results = V] (Evals)[accesses = Q; changes = D; results = W]---------------------------------------------------------- (EvalsRule)(Evals)[accesses = P + Q; changes = C + D; results = V + W](https://image.slidesharecdn.com/reverseengineeringandtheorybuildingv3-110806065205-phpapp02/85/Reverse-engineering-and-theory-building-v3-25-320.jpg)
![Borrowing (modified)publicsynchronized void borrow(Messagem) {int id = (int)m.getData(0); String name = (String)m.getData(1); Reader reader = getReader(id); Book book = removeBook(name); Book[] borrowed = borrows.get(id);if(borrowed.length < BORROW_LIMIT) { Book[] updated = new Book[borrowed.length+1];Array.copyInto(borrowed,updated);updated[borrowed.length] = book;borrows.put(reader,updated);m.reply(OK); } else m.reply(FAIL);}](https://image.slidesharecdn.com/reverseengineeringandtheorybuildingv3-110806065205-phpapp02/85/Reverse-engineering-and-theory-building-v3-33-320.jpg)
Reverse engineering and theory building v3
- 1. Reverse Engineering as Theory BuildingTony Clark t.n.clark@mdx.ac.ukBalbir Barn b.barn@mdx.ac.ukSchool of Engineering and Information SciencesUniversity Of MiddlesexLondon, UK
- 2. OverviewMotivation:Houston, we have a problem.Surely this has been done before?Theory Building:An approach: Old wine in new bottles.Some technology: New wine in old bottles.Case Study:But what might it look like?
- 3. Motivation: There is nothing new under the sun.
- 4. The business driverSoftware Outsourcing IncHigh value software maintenance contractsOutsourcing of source code maintenance of large scale legacy systemsCritical operational systemsInitial contract is limited length – achievement of maintenance requests will lead to longer contract.IssuesSupport for responding to rapid ad hoc requests for changes to systemLack of documentationOriginal software developers no longer at the customer companyA common scenario facing many Indian IT providers
- 5. Naur’s Theory of ProgrammingSeminal paper written in 1985Fundamental assertion:Programmers achieve a certain insight or theory of some aspect of the domain that they are addressingBased on Ryle (1949) – A person who has a theory or facts can do things and explain why and respond to questionsExplains this in the context of the software lifecycleTraditionally software methods are focused on artifact production (explicit knowledge). But should be focussed on techne and phronosis (wisdom derived from practice)
- 6. Naur’s Thesis: FeaturesProgramming is Theory Building.Understand the domain as a theory.Theories consist of information bearing statements about a domain that are true (or false).No such thing as the ideal theory because:many consistent (incomplete) theories.theories are personal.theories consist of information necessary for stakeholder.
- 7. Systems lifecycle and theory buildingTheory buildingTheory DecayAnalysis and DesignImplementationMaintenanceDeployed SystemOnce the system is deployed and enters into a maintenance phase, the only way the theory can be retained is by transfer of knowledge between team members.The artifacts represent an incomplete documentation of the theory
- 8. Naur’s Thesis: Benefit ClaimsCore IPR is in theories.Theories are more abstract than programs.Maintain system using theories.Introduce new people using theory not code.Theories are reusable (code fails to be).Theories allow questions to be articulated.Theories capture different views of a system.
- 9. Understanding is Theory Building
- 10. What do we currently do?Program Code:Just look at the code.Misunderstandings because:the domain is weakly represented in the code.unable to articulate questions.UML Models:Weakly expressive:Static models are OK.Dynamic models lack completeness.Meaning is bound up with translations to code.Modularity cannot be applied to understanding: have to state the whole thing – no real views.
- 11. Naur’s Thesis Applied to ModellingWhat’s the difference between modelling and programming?If programming is the construction of a theory that is then mapped to an implementation (theory) then: Modelling smells like programming to me.What’s the difference between modelling and domain specific modelling?A theory building framework gives us a context in which this can be analyzed.
- 12. Approach: Building theories about an application.
- 13. Theory Building ProcessUserInterfaceobservationSystem ExecutionsinteractionSourceCodeModels(static, dynamic, security, etc.)Theorems(aspects)formulationinspectionmodificationgroundingDocumentationcomprehensionabstractionPartialTheoriesExpertKnowledgeacquisitionslicingaggregationTheory
- 14. What is a theory?theorem: true or false statements.theory: collections of theorems.axioms: statements that are givens.rules: ways of constructing theorems.mappings: between theories (and theorems)combinations: composing theories (and theorems).initial: an initial theory maps to all the others.terminal: every theory maps to a terminal theory.
- 15. Being Concrete: Aspects of a Simple Case Study
- 16. Customer RequirementSoftware maintenance contract with a Library.They have software controlling borrowings at multiple terminals.Originally sourced from a third party.They have lost the documentation.They have the source code.Occasionally they have noticed books going missing.Under the contract your company needs to identify and fix the problem.
- 17. Library Source Codeclass Library { Vector<Reader> readers; Vector<Book> books;Hashtable<Reader,Book[]> borrows;intnextReaderId; public void handle(Messagem) {switch(m.id) {case REGISTER:register(m);break;case ADD_BOOK:add_book(m);break;case BORROW:borrow(m);break; ...} } ...}application stateentry pointinterface
- 18. Library Operationspublic void register(Messagem) { String name = (String)m.getData(0);if(hasReader(name) == false) {intid = allocateReaderId();readers.add(newReader(name,id));m.reply(id); } else m.fail();}message argsguarddata accessmessage reply
- 19. Borrowingpublic voidborrow(Messagem) {int id = (int)m.getData(0); String name = (String)m.getData(1); Reader reader = getReader(id); Book book = removeBook(name); Book[] borrowed = borrows.get(id);if(borrowed.length < BORROW_LIMIT) { Book[] updated = new Book[borrowed.length+1];Array.copyInto(borrowed,updated);updated[borrowed.length] = book;borrows.put(reader,updated);m.reply(OK); } else m.reply(FAIL);}data accessdata access
- 20. Static Modelling
- 21. Commands
- 22. Data Access
- 23. Results
- 24. Partial Theories are Defined by Rulesr = (Reader)[name = n; id = i]not(R->includes(r))---------------------------------------------- [EvalRule] (Eval)[ data = (AddReader)[name = n]; result = (ReaderAllocated)[id = i]; change = (StateChange)[ pre = (Library)[ readers = R; books = B; borrows = X; nextReaderId = i]; post = (Library)[ readers = R->including(r); books = B; borrows = X;nextReaderId = i+1 ] ] ]
- 25. Evaluating More than one Data Access(Evals)[accesses = Seq{}; changes = Seq{}; results = R] (EvalsRule) (Eval)[data = a; change = c; result = r]--------------------------------------------------------- (EvalsRule)(Evals)[accesses = Seq{a}; changes = Seq{c}; results = Seq{r}] (Evals)[accesses = P; changes = C; results = V] (Evals)[accesses = Q; changes = D; results = W]---------------------------------------------------------- (EvalsRule)(Evals)[accesses = P + Q; changes = C + D; results = V + W
- 26. Library Theory
- 27. TheoremsCan someone borrow a book without joining the library?Can two people join the library with the same id?Is it possible to construct a situation where a book disappears from the library?
- 29. Fill in the Blanks2
- 31. DeductionDeduction: Theory tells us there must be two cards for fred.Reality: Fred must have duplicated the library card and an accomplice borrows the second book at the same time when fred borrows the first.Solution: change the theory.
- 33. Borrowing (modified)publicsynchronized void borrow(Messagem) {int id = (int)m.getData(0); String name = (String)m.getData(1); Reader reader = getReader(id); Book book = removeBook(name); Book[] borrowed = borrows.get(id);if(borrowed.length < BORROW_LIMIT) { Book[] updated = new Book[borrowed.length+1];Array.copyInto(borrowed,updated);updated[borrowed.length] = book;borrows.put(reader,updated);m.reply(OK); } else m.reply(FAIL);}
- 34. ConclusionUnderstanding is theory building.Modelling and programming are essentially the same.Modelling aims to be initial.Programming needs to be terminal.Modelling languages should support theories.Theories need to support:translation through mappings.different views through combination.patterns through parameterization.