Why do we use UseCase diagrams in object oriented analysis and design even if Usecases are not considered as Object oriented?

Question

UML notations says, Usecases are drawn to point out the functional requirements in the Problem Domain, it by no means gives the information about object or class as Data Flow Diagrams or Entity Relationship diagrams. But also why do we use Usecase Diagrams in object oriented analysis and design even if Usecases are not considered as Object oriented.

Answer 1

Use case diagram is meant to shed light on the main functionalities of the system , and emphasis the perspective presenting the latter as a blackBox merely existing for a sole mission;deliver to the actor the Promised service .

At this point we don't realy care about OOP realy , as you can definetly use Use case diagram for any other type of analysis.

UML is just a set of visual tools to allow a unified expression of different perspective of the system. In Case you are using The Unified Process it advocates to start with identifiying the use cases first then explode every use case into collaborative entities (classes) and establish the static collaboration between them by harnessing the Class Diagram toolbox.

Answer 2

Object-oriented is analysis and design methodology, while use case is requirements methodology. And be aware of the core development workflow：

1. Business modeling
2. Requirements
3. Analysis
4. Design

If we use UML to do these works, we may have:

1. Business use case+ Business sequence diagram
2. System use case+ System use case specification
3. Analysis class diagram+ Analysis sequence diagram+ Analysis state machine diagram
4. Code, Database......

UML diagrams in 3. can be replaced by DFD/ER