用例图-参与者

Question

I need to create a Use Case diagram using the following scenario, this is all I have to work with so it should work according to this.

My Actors are - Buyer, Seller and User (I think)

Scenario

The eAuction system allows multiple users to conduct auctions electronically. Once a user has setup an account, they are able to act as a seller and start an auction by listing an item to be sold. They may also act as a buyer by browsing auctions that are in progress and bidding on any item whose auction has not closed. A user does not need to setup an account to simply browse auctions in progress.

An auction is started when a seller inputs data including, a description of the item, the starting price, the reserve price and a date when the auction will close. The system enforces an upper and lower bidding increment of 20% and 10% of the starting price respectively. The system also enforces a closing date ≤ 7 days from the current date. Once the data has been input, the auction automatically becomes pending and the seller must verify the auction before it starts.

When a user wants to make a bid against an item, they must first locate the auction in question by browsing the auctions that are in progress. They may then make a bid that the system must check is within the upper and lower bidding increment amounts. Each auction keeps track of every bid made against the item. Once the auction closes the system checks to see if the item's reserve price has been met and if so, informs the buyer with the highest bid of their victory. If the item's reserve price has not been met, the system informs every buyer who made a bid and the auction is closed.

Both sellers and auctions may be temporarily blocked which prevents the sellers from logging on or the auctions from being browsed or bid upon respectively.

Answer 1

Yes, they are. An actor represents a role someone or something plays with respect to the system under consideration (SUC). It does not matter on its physical representation. Anyone can act in any role towards the SUC. Restrictions, if any, can be expressed as constraints attached to the actors (eg { a Seller may not act as Buyer in the same UC} ).

There are quite a number of use cases. The first is Setup account which enables Auctioneer to start auctions. He has List item for auction as next UC. And Buyer has Bid for listed item . I'm not sure about closing the auction. Maybe, if like on ebay, this is done by a Timer actor which has Close auction be performed after a certain time. Also not sure about the blocking condition. This can be expresses as a constraint. But there might as well be a Watcher actor who blocks users according to a rule set. Just start by placing those UCs and the according actors on a UC diagram. Then start discussing with stakeholders about the completeness. You will eventually find more actors and UCs.