UseCases

A use Case Diagram Describes the Communication flow ( Request & Response) between the external user and the system / Internal communication between 2 different components.

The Technical usecase Describes the Requirement Details; The Technical usecase for a Requirement has the below details

UseCaseID : A Unique ID for the usecase
UseCaseName : Name of the USeCase
Goal : What is the purpose of the usecase and output
Actor : The users who will have permission to interact with the system
Description : Describe about the functionality of the Requirement
PreConditions : The Preconditions to be satisfied for the requirement to be started
PostConditions : The final output after execution of the requirement
Exceptions : Describes any exceptions / errors might occur during execution of the Req.
Priority : Priority of the Requirement High / Medium / Low
Fequency of use : How frequently the requirement is used in the application
Assumptions : List any assumptions made by the Analyst during the preparation of the Req Details
Check the below doc
www.processimpact.com/process_assets/use_case_template.doc

The below links also Provide you good information on usecases Diagram for ATM Functionality
http://courses.knox.edu/cs292/ATMExample/UseCases.html