1. SYSTEMSDESIGNANALYSIS 1 Chapter 22 Object-Oriented Design Jerry Post Copyright © 1997

2. SYSTEMSDESIGN 2 A Short History  Traditional Programming  Every program written by individuals.  Repetitive, keep needing to solve the same problems.  Bugs  Goal: Reusability  Create a library collection of objects that can be used in any program.  Windows Programming  Huge amount of material to learn about windows.  Event-driven  Mostly repetitive Create a window Actions (open, close …) Scroll bars, etc.  Commercial Software  Best to buy as much software as possible.  Development is expensive.  Example: DBMS, spreadsheet, etc.

3. SYSTEMSDESIGN 3 Objects and Properties  Objects (entities)  Something we wish to identify or track, e.g., Employee Product Customer  Objects can be found within processes  Objects will become tables  Objects are described by Properties (attributes)  Examples Employee ( ID, Name, DateHired, Department...) Product (ID, Description, ListPrice,...) Customer (ID, Name, Address, Telephone,...)  A specific instance of an object is uniquely identified, e.g., an Employee ID identifies exactly one employee

4. SYSTEMSDESIGN 4 Objects and Classes  Class: generic description  Object: specific item, with data.  Class definition--encapsulation  Class Name  Properties  Methods  Inheritance Relationships  Derived classes  Focus on differences  Polymorphism Methods with the same name. Activated depending on the class of the object. Accounts Account# Customer# DateOpened CurrentBalance OpenAccount CloseAccount Class name Properties Methods Savings Accounts InterestRate PayInterest Checking Accounts MinimumBalance Overdrafts BillOverdraftFees CloseAccount Inheritance Polymorphism

5. SYSTEMSDESIGN 5 Objects & Events EventsMethodsObjects Sale Record Sale Update Inventory Notify Customer Service Transaction Log Accounts & Ledgers Inventory Customers Employees (commissions) Inventory Order/JIT Notify Suppliers Schedule Payment Accounts & Ledgers Suppliers Shipping/Receiving Installation & Maintenance

6. SYSTEMSDESIGN 6 Events and Triggers  Business processes or events can be represented as triggers.  A form, or a change in the data can cause the DBMS to trigger a subroutine which alters additional data.  An event can cause an object to send a message to another object--changing a property, or activating a method. Ship Order Order form Invoice Adjust Inventory Items shipped Inventory changes Analyze Inventory Level Inventory data changes Reorder items trigger

7. SYSTEMSDESIGN 7 Event Triggers  Business Process: Ship Product  Trigger: Inventory Change  Executes function/trigger in Inventory object.  Object: Inventory  Property: Current Inventory.  Function: Update Inventory.  Trigger: On Update, call Analyze function.  Process: Analyze Inventory  Function: Determine need to reorder.  Trigger: Generate new order. Analyze Inventory Order Inventory Ship Product Trigger Inventory Change Trigger Analysis Trigger Inventory Order

8. SYSTEMSDESIGN 8 State Diagrams  Objects often have a state  It represents the current status of the object.  It is changed or triggered by an event.  Example (book): train Stopped Running Unloading  State diagram shows how object’s state is changed by other objects and events. State = Stopped Train State = Running State = Unloading Notice the train cannot get to the unloading state from the running state. Heater: State = off Heater: State = on Thermostat message State change

9. SYSTEMSDESIGN 9 SDLC v. Object Oriented