Use case diagrams are known as the information about whole system with drawn syntax.The article just before that i have talked about a system: a dynamic web site system the use case diaram below belongs to the same example.

Also some explanations about the diagram as:

Use Case UC1 : Upload&Download Process
Primary Actor : Administrator
Steakholders & Interests:

1. Administrator : Wants all rights to manage the site in minimal time and effort. Also their need is to achieve the site to manage it from every computer they want which by they can access to the Internet.
2. Student : Wants reach to the documentations that he/she needs to download, and add comments to the annocuments also posting messages to the admins. These process needed to be done in a small time period.
3. Invited Speaker : Wants the rights for to add the documantations for their class in minimal effort.To get these rights they need to enter the web site by their user names and mail adresses that they reported to the admins before.
4. Guest : Just can read the page and post messages. Also become a member of the site with his/her student number.

Preconditions : Administrator has logged in to the site by using their username and password.
Success Guarantee (Postconditions) : Text is uploaded succesfully. Web site updated.


Main Success Scenario:

1. Administrator opens his/her control panel.
2. Administartor writes down the address of the document that he/she want to upload.
3. Database stores the document file.
4. Student/Invited Speaker /Guest reads the document from website.
5. Student & Invited Speaker downloads the document.
6. Administrator delete the document link from website.

Extensions:

At any time system fails:
3.a. Database can not stores the file.
3.b. Wrong document file’s address entry by Administrator.
5. Student & Invited Speaker can not dowload the file since the system errors.

For next article the activity diagram of the same example will be axplained.