I am working on a project which is basically requiring the installation of 2 components of an existing (third-party vendor) system.  I've captured both the business/system requirements, and don't believe it is necessary nor will serve as benefit to try and develop use cases for an already-built system.  I do believe that we will need system (interface) use cases. I am trying to get my hands on the vendor's system documentation to see if they currently have any existing use cases developed outlining the various actors and their interaction with the 2 components/modules that we are installing.  Any thoughts?

C,

The assumption here is you must have done some Requirements for you to have purchased/contracted the extra two modules that now need implementation. Review the end-to-end processes and in particular, review the activities that use/involve the new modules.

Not knowing your applications, but lets say the new Modules allow  you to ship directly from supplier warehouses. Eg. New WOW (way of working): Customer buys an iPad on your website but Apple ships the product direct to the customer. Prior to implementation of this module (the old WOW) Apple first shipped the iPad to your warehouse, then you shipped it to the Customer.

Now the above scenario identifies a change in process and you would need some use cases (narrative format) to list the changing processing steps. This bit helps a lot with testing the modules as part of the new WOW.

All the best!

K