As part of what is called the E-Gov Initiative, government agencies at the Federal, state and local level are working to pay their bills electronically.

A key component of electronic payments by government is an External Certification Authority (ECA) certificate, which enables secure payment transactions.

Vendors working with government obtain these certificates through a private sector contractor called Verisign.

Government e-payments using ECA certificates have simplified the payment process greatly.

Here is how the system works.: Contractor A submits an electronic invoice by going onto its e-payments website, as established by Verisign.

This website enables Contractor A to review information on government Agency policy, to download documents and forms, to review payment status at different client agencies, and - most importantly - to submit electronic invoices for work done. Electronic invoice submissions are forwarded directly to the Agency accounting office and to the government Contracts Office.

The function of the Agency accounting office is to acquire the funds to pay the invoice. The function of the Contracts Office is to approve or disapprove the requested invoice.

If the invoice is approved, payments are quickly made by the accounting office to the Contractor. If the invoice is disapproved, payments are not made.

Create a use case diagram that captures the scenario described above.