...
We have chosen to segment customer requests into a few distinct request types and tables illustrated in the diagram:
The service catalog offers services to the end user that may be created in one of three tables: Service Requests, Purchase Requests, or Change Requests. Whether or not a particular group of users can request particular services can depend on their group permissions – for instance, our default internal end users cannot directly create a Change Request, while technical users can. An end user may also submit an incident to report a problem or interruption to a business or technical service. If merited, that incident may lead to the creation of a Problem and a Change Request by technical staff.
...