1. Objectives:1. Classes and Objects 2. Attributes 3. Services 4. Subjects Object-Oriented Analysis – Finding Class-&-Obects

2. Finding Class-&-Objects  Object:  An abstraction of an entity in the problem domain.  Class:  A description of one or more Objects with a uniform set of Attributes and Services  Class-&-Object:  A Class and the Objects that make up the Class.

3. Finding Class-&-Objects  Bring the technical representation of a system as close as possible to the real world situation you are working with.  Create a stable foundation for analysis and specifications now and in the future.  Provides stability when moving from systems analysis to design.

4. Finding Class-&-Objects  The investigative process consists of:  First-hand observation  Listening actively to the experts  Reviewing any previous OOA results

5. Finding Class-&-Objects  Checking other systems  Reading carefully all documentation from the client  Building a prototype  Summarizing

6. Classes vs. Objects  Object is an instance of some class  Classes have zero or more instances  Classes are static  Objects are created and destroyed Air Traffic Control System Abstractions (Classes)Objects planesNew runways flight plansNew flight plans runwaysNew planes enter air spacesan airspace

7. Requirements  Product Description  Business Solution Description  Goal: Concrete Description understandable to the user  Domain Analysis  Problem Analysis  Applied only to new, difficult, or unsolved problems  Goal: Complete understanding of the solution and constraints on business solutions

8. Problem Analysis  Developers acquire knowledge of the system  Identify possible constraints on business solution  Interview business domain experts  Issues to be addressed:  find a way to trade off constraints  find ways to organize the information

9. Business Solution Description  Describe the external behavior of the product to be built  Issues to be addressed:  ideals are organized  conflicting views are resolved  inconsistencies and ambiguities are eliminated

10. Business Solution Description & Problem Analysis should produce a model that:  Organizes the data into objects and classes, and gives the data a structure via relationships of inheritance, aggregation, and association.  Specifies local functional behaviors and defines their external interfaces (service prototypes)  Captures control or global behavior  Captures constraints (limits and rules)

11. Suggested Approach for Finding Objects - Step 1  Use Nouns  Pioneered by Abbott and popularized by Booch  Obtain an informal requirements document  Use nouns, pronouns, and noun phrases to identify objects and classes

12. Suggested Approach for Finding Objects - Step 1  Identify Objects  Singular proper nouns  Jim, he, she, employee number 5, my workstation, my home  Nouns of direct reference  The sixth player, the one-millionth purchase

13. Suggested Approach for Finding Objects - Step 1  Identify classes  Plural nouns  People, customers, vendors, users, employees  Common nouns  Everyone, a player, a customer, an employee, a workstation

14. Suggested Approach for Finding Objects - Step 1  Identify Operations  Verbs  Pay, collect, read, request  Predicate phrases  Are all paid, have simultaneously changed  Identify Attributes  Nouns related to the class nouns  Name, height, weight

15. Suggested Approach for Finding Objects - Step 1  Indirect approach to finding objects and classes  Nouns are not always classes or objects in the problem domain  Used to find potential objects and will not find all the objects

16. Suggested Approach for Finding Objects - Step 2  Interactive dialog with the domain expert  Domain experts commonly make mental models and work with abstractions to deal with complexity of their respective business  See dialog on p. 40-41 of Teach Yourself UML  Identify all the objects that the domain experts identify

17. Suggested Approach for Finding Objects - Step 3  Identify the Things to be Modeled in the Application domain  Persons, roles, organizations, locations, logs, reports, forms, concepts, events  This helps to trigger our recognition of potential objects

18. “Things to be Modeled” Coad and Yourden CategoriesExplanation Structure “Kind-of” & “Part-of” Other Systems External Systems Devices Events Remembered A historical event Roles Played Roles user play Location Organization Units Groups to which the user belongs

19. “Things to be Modeled” Shlaer and Mellor CategoriesExplanation Tangibles Cars, telemetry data, sensors Roles Mother, teacher, programmer Incidents Landing, interrupt, collision Interactions Loan, meeting, marriage Specification Product spec, standards

20. “Things to be Modeled” Ross CategoriesExplanation People Humans who perform some function Places Areas set aside for people or things Things Physical Objects Organizations Collections of people having a defined mission Concepts Non tangible ideas Events Things that happen

21. Suggested Approach for Finding Objects - Step 4  Eliminate false problem domain objects  Is it a real world entity?  Is it important to the discussion of the requirements?  Does it have a crisply defined boundary?