1. Software Development 2D1385 Karl Meinke NADA KTH karlm@nada.kth.se

2. 1.1. Lab Exercises Labs 1,2 Java API, Graphics, event handling Lab 3 client-server with sockets Lab 4 XML, syntax and parsing Lab 5 interprocess communication with CORBA Lab 6 build a web browser using Java Swing components

3. 1.2. Course Book “Software Design” by Eric Braude, 2004 Chpt: 0-2 Programming Concepts 3: Unified Modeling Language UML 4-5: Software Design Principles 6-9: Design Patterns 10-12: Software Components (Beans.NET) 13-14: Software architecture

4. 1.3. Goals of the Course Software Design Theory and Practice Starts where programming and data structure courses end Understanding how to satisfy requirements specifications (application is correct and adequate) Obtain robust, flexible reusable applications Apply abstraction, encapsulation and modularity

5. 1.4. Good Program Modules A program module should be simple, clear and minimal It shouldn’t surprise the end-user Dependencies between modules should be few Modules should be usable, correct, robust, flexible and maintainable.

6. 1.5. Checklist for Submitting Work Which engineering/management model has been used? Show your UML –diagram for the lab Demonstrate using a program execution that the functional and design requirements are satisfied Explain how robustness, and reusability are satisfied

7. 1.5. Checklist (2) How have you achieved abstraction, encapsulation and modularity Which design patterns have been used? Which classes have you reused from earlier labs? (With refactoring?) Which new classes have you used, and why?

8. 1.5. Checklist (3) How have you performed functional testing? How have you documented your program (comments, javadoc etc.) Point out the most critical pieces of code. In retrospect, what would you have done differently if the project had continued?

9. 1.6. UML The Unified Modeling Language (2.0) Class/Object diagrams (static) Sequence diagrams (dynamic) Activity diagrams (dynamic) Statecharts (dynamic) Standard developed by OMG adopts earlier ideas (Booch, Rumbaugh, Jacobson)

10. 1.6.1. Models Models express requirements, architecture & detailed design. (Video Game examples) Use Case Model: In this situation do the following … e.g. how to engage a foreign character

11. Object / Class Model: with objects of these classes … Object provides a set of services, e.g. engagement class. State Model: by reacting to these events … state/event  reaction e.g. if foreign character shoots while we are friendly … run away

12. Data Flow Model: in this way … e.g. bullet objects flow from foreign character object to player object. Target App Use CasesClass Model State Model Data Flow

13. 2. O-O Analysis & Design The basic OOA&D approach (iterative) 1.State the main use cases 2.Convert the use cases to sequence diagrams 3.Select the resulting domain classes 4.If not finished goto 1.

14. 2.1. UML Use Case Diagrams UML gives us a graphical language to organize all our use case scenarios into one overview: Use Case Diagrams These display: actors use cases associations, i.e. which actors are involved in which scenario

15. Activate Check in Check out Add video Clerk Stocker Precondition: app has been activated 1.Actor clicks “ check out ” 2.Actor swipes bar code …. Postcondition: video is registered to customer

16. 2.2. Use Case Modeling In O-O based IT projects, we can begin the requirements analysis phase with a Use Case Analysis A use case is a common or representative situation where one or more external users and/or systems interact with the system to solve an instance of a common problem

17. Notice the underlined word “common” Software seems to obey the statistical Pareto Law 90% of time is spent executing just 10% of the code Therefore care in designing just this 10% of code is “cheap” and will give a good product 90% of the time (at least in theory!)

18. Note: we want to decouple specific users (e.g. John Smith) From their roles, e.g. student, teacher, systems administrator, etc. A role will be called an actor. A specific proper noun (object) e.g. Karl Meinke, may play several roles: teacher, researcher, sysadmin...

19. Use Case Modeling involves three steps that may be repeated until we are satisfied. Step 1. Identify, name and define each actor in terms of: (a)Goals, i.e. what the actor wants to do, (b)Needs, i.e. what services from the system the actor requires to meet each goal.

20. Step 2. For each system service (identified in Step 1), informally describe the preconditions and results of the service, and its, interaction with the actors in: –a typical case (sunny day scenario). –exceptional and error cases (rainy day scenario) Such a service description is called an informal description of a use case scenario.

21. Step 3. For each informal description which is: –mission critical –unclear, or –ambiguous formalise the interaction of the system and the relevant actors using a sequence diagram

22. Step 4. [If necessary, repeat Steps 1-3] Makes an iterative requirements analysis 1. Actors 2. Use cases 3. Sequence Diagrams

23. 2.3. Example Let us analyse requirements on a Warehouse management system Step 1. We begin by identifying actors (perhaps by looking at a particular warehouse and identifying job titles). This might give the following:

24. Foreman: responsible for one warehouse. Warehouse Worker: works in a warehouse loading and unloading goods. Truck Driver: drives a truck between different warehouses Forklift Operator: drives a forklift in a warehouse Office Staff?, Customers? Security Staff?? … Table 2.3.1

25. These actor definitions are short, but enough to get started on Step 2. By iterating again later we can add more details. Step 2 asks to focus on the services which the system (warehouse management software) must provide. We build a list of informal use case scenarios.

26. Notice how in Table 2.3.1 we underlined: Nouns: e.g. foreman, warehouse, … Verbs: e.g. loading, unloading … Relational Phrases: e.g. responsible for, works in, … (prepositions?) (Notice the possible overlap between verbs and relational phrases.) This identification work is the heart of O-O analysis and design, since …

27. 2.3.2. Central O-O Dogma Common Nouns e.g. warehouse, truck, correspond to classes and attributes Proper Nouns e.g. Karl, Fido, KTH, correspond to objects Verbs e.g. unload, correspond to methods Relational Phrases e.g. responsible for, works with correspond with system and/or software “structure”

28. Not every noun will be an actor … (does a forklift truck have any goals ???) … but every actor will be a noun, so: Actors  Nouns

29. Step 2 requires us to look at each actor in turn (in our case there are 4 actors) and ask: What does this actor want to do (all verbs)? What does the actor need from the system to accomplish each activity (each verb)? Let’s look at the 1 st actor “foreman” and try to analyse the verb “responsible”.

30. (a) A foreman has to be able to move items between warehouses with or without a customer order. This use case scenario is called “manual redistribution between warehouses” (b) A foreman also wants to check how far a customer order has been processed. We call this use case scenario “check status of a customer order”.

31. Let’s try to informally define the 1 st use case scenario: “manual redistribution between Warehouses”. This could be broken down into 4 steps (1)Initialisation: when a foreman gives a request to do a redistribution.

32. (2) Planning: when the system plans how to co-ordinate the various transports, and issues transport requests (3) Loading: when a truck fetches the items from a source warehouse. (4) Unloading: when a truck delivers items to a destination warehouse.

33. Is there anything wrong with this use case? (1)It is very short! - but we can add detail later! (2)It doesn’t say what happens if things go wrong. - We need to add exception/error cases. - The more of these we add, the more robust our system will be.

34. 2.4. UML Sequence Diagrams A use case scenario describes a sequence of interactions or messages between a collection of actors and the system in order to carry out some task

35. Often we would like to formally model a use case scenario, to study: timing aspects (relative or absolute) communication patterns system states exception behavior alternative paths or behaviors

36. 2.4.1. Elementary Concepts A basic sequence diagram depicts a set of objects or processes each of which has its own timeline. Conventionally, objects go across the diagram horizontally, while time goes down the diagram vertically. Down the timelines, between objects, we show messages.

37. C : ComputerP : Print_serverD : Device >lpr file print(file, device) print(file,size) done >done (time) Here is our earlier sequence diagram drawn as an SD/MSC: object/process timeline message time SD Print

38. Notice that: This basic SD has 3 objects and 6 messages 1 message comes from the environment: >lpr file (from the keyboard??) 1 message goes to the environment >done(time) (to the screen??) The environment is an implicit actor Each timeline has a terminating block at the bottom, which does not mean that the object dissappears/ gets deleted, life goes on!!

39. 2.4.2. The Time Concept An SD/MSC must show dynamic behavior over time Down each timeline we see a set of events. Each event may either be: sending of a message (arrow tail) receiving of a message (arrow head)

40. Each timeline shows the local relative order between events, but not the absolute time interval between events. Thus the basic model of time is relative (instead of absolute). Also, for every message m: send(m) occurs before receive(m)

41. This means that, e.g. receive(>lpr file) occurs before send( print(file, device) ) which occurs before receive(done) which occurs before send(>done(time) ) and e.g. send(done ) occurs before receive(done )

42. We don’t know the absolute time between sending and receiving a message, i.e. message delay. e.g these two diagrams express the same scenario. B A AB “a” “b” “a” “b” SD 1 SD 2