CSCI 383

1. CSCI 383 Object-Oriented Programming & Design Lecture 8 Martin van Bommel

2. Intelligent Interactive Kitchen Helper • Imagine you are the chief software architect in a major computing firm • One day your boss rushes into your office with a specification for the next PC-based product. It is drawn on the back of a used dinner napkin, in handwriting that appears to be that of your boss • Briefly, the Intelligent Interactive Kitchen Helper will replace the box of index cards of recipes in the average kitchen CSCI 383 Lecture 8 M. van Bommel

3. Your Job • Your job is to develop the software that will implement the IIKH CSCI 383 Lecture 8 M. van Bommel

4. Abilities of the IIKH • Here are some of the things a user can do with the IIKH [identified as a result of a use-case analysis]: • Browse a database of recipes • Add a new recipe to the database • Edit or annotate an existing recipe • Scale a recipe for some number of diners • Plan a meal consisting of several courses • Plan a longer period, say a week • Generate a grocery list that includes all the items in all the menus for a period CSCI 383 Lecture 8 M. van Bommel

5. Scenarios • A scenario is an instance of a use case • It expresses a specific occurrence of the use case • A specific actor ... • At a specific time ... • With specific data • Can be part of the Description field of a use case CSCI 383 Lecture 8 M. van Bommel

6. An Example Scenario Alice Smith sits down at her computer and starts the IIKH. When the program begins, it displays a graphical image of a recipe box and identifies itself as the IIKH, product of IIKH incorporated. Alice presses the return button to begin. CSCI 383 Lecture 8 M. van Bommel

7. An Example Scenario (cont’d) In response to the key press, Alice is given a choice of a number of options. She elects to browse the recipe index, looking for a recipe for salmon that she wishes to prepare for dinner the next day. She enters the keyword “salmon” and is shown in response a list of various recipes. Alice remembers seeing an interesting recipe that used dill weed as seasoning. She refines the search, adding the phrase “dill weed”. This narrows the search to two recipes. CSCI 383 Lecture 8 M. van Bommel

8. An Example Scenario (cont’d) Alice selects the first. This brings up a new window in which an attractive picture of the finished dish is displayed, along with the list of ingredients, preparation steps, and expected preparation time. After examining the recipe, Alice determines it is not the recipe she wanted. She returns to the search result page and selects the second alternative. Examining this dish, Alice decides this is the one she had in mind. She requests a printout of the recipe, and the output is spooled to her printer. Alice selects “quit” from a program menu, and the application quits. CSCI 383 Lecture 8 M. van Bommel

9. Software Components • A software component is simply an abstract design entity with which we can associate responsibilities for different tasks • May eventually be turned into a class, a function, a module, or something else • A component must have a small well defined set of responsibilities • A component should interact with other components to the minimal extent possible CSCI 383 Lecture 8 M. van Bommel

10. CRC Cards • Components are most easily described using CRC cards. A CRC card records the name, responsibilities, and collaborators of a component • Inexpensive, Erasable, Physical CSCI 383 Lecture 8 M. van Bommel

11. CRC Cards (cont’d) • Responsibilities • Express responsibilities as short verb phrases containing active rather than passive verbs • Define what should be done, not how to do it (declarative) • Include only essential information, not a great deal of detail • Collaborators • A collaborator for a class or object is another class or object with which the first class communicates to carry out its responsibilities • The sender of a message usually is not one of the collaborators of the receiver CSCI 383 Lecture 8 M. van Bommel

12. CRC Cards (cont’d) • Identify an initial set of classes and objects. Can be done by performing a “grammatical parse” on scenarios or use case descriptions. Create one card for each • Identify an initial set of responsibilities and collaborators for each card. This may lead to the identification of other classes and objects • Spread the cards out on a desk, attach them to a wall, or, for a group project, assign one or more cards to each person in the group • Run through usage scenarios; as the flow of control passes to an object or class, bring that card to a prominent spot • As the scenarios are played out, gaps in the design are filled in. This is a form of iterative refinement CSCI 383 Lecture 8 M. van Bommel

13. A Component, The Greeter • Let us return to the development of the IIKH. The first component your team defines is the Greeter. When the application is started, the Greeter puts an informative and friendly welcome window (the greeting) on the screen CSCI 383 Lecture 8 M. van Bommel

14. A Component, The Greeter (cont’d) • Offer the user the choice of several different actions • Casually browse the database of recipes • Add a new recipe • Edit or annotate a recipe • Review a plan for several meals • Create a plan of meals • Many of the details concerning exactly how this is to be done can be ignored for the moment CSCI 383 Lecture 8 M. van Bommel

15. A Component, The Greeter (cont’d) • CRC card? CSCI 383 Lecture 8 M. van Bommel

16. The Recipe Database Component • Ignoring the planning of meals for the moment, your team elects to next explore the recipe database component • Must Maintain the Database of recipes • Must Allow the user to browse the database • Must permit the user to add a new recipe • Must permit the user to edit or annotate an existing recipe CSCI 383 Lecture 8 M. van Bommel

17. The Who/What Cycle • As we walk through scenarios, we go through cycles of identifying a what, followed by a who • What action needs to be performed at this moment, • Who is the component charged with performing the action • Every what must have a who, otherwise it simply will not happen. • Sometimes the who might not be obvious at first, i.e., who should be in charge of editing a recipe? CSCI 383 Lecture 8 M. van Bommel

18. Postponing Decisions • Many decisions, such as the method of browsing, can be ignored for the moment, as they are entirely encapsulated within the recipe database component, and do not effect other components • Scroll bars and windows? • A virtual “book” with thumb-holes and flipping pages? • Keywords and phrases? • Only need to note that somehow the user can manipulate the database to select a specific recipe CSCI 383 Lecture 8 M. van Bommel

19. Responsibilities of a Recipe • We make the recipe itself into an active data structure. It maintains information, but also performs tasks • Maintains the list of ingredients and transformation algorithm • Must know how to edit these data values • Must know how to interactively display itself on the output device • Must know how to print itself • We will add other actions later (ability to scale itself, produce integrate ingredients into a grocery list, and so on) CSCI 383 Lecture 8 M. van Bommel

20. The Planner Component • Returning to the greeter, we start a different scenario. This leads to the description of the Planner • Permits the user to select a sequence of dates for planning • Permits the user to edit an existing plan • Associates with Date object CSCI 383 Lecture 8 M. van Bommel

21. The Date Component • The Date component holds a sequence of meals for an individual date • User can edit specific meals • User can annotate information about dates (“Bob's Birthday”, “Christmas Dinner”, and so on) • Can print out grocery list for entire set of meals CSCI 383 Lecture 8 M. van Bommel

22. The Meal Component • The Meal component holds information about a single meal • Allows user to interact with the recipe database to select individual recipes for meals • User sets number of people to be present at meal, recipes are automatically scaled • Can produce grocery list for entire meal, by combining grocery lists from individual scaled recipes CSCI 383 Lecture 8 M. van Bommel

23. The Six Components • Having walked through the various scenarios, you team eventually decides everything can be accomplished using only six software components • You can at this point assign the different components to different programmers for development CSCI 383 Lecture 8 M. van Bommel

24. Interaction Diagrams • The picture on the previous slide captures static relationships, but not the dynamic flow of messages in a scenario. That information can be recorded by an interaction diagram CSCI 383 Lecture 8 M. van Bommel