How does Web Source operation's URL Pattern get it's argument when it's assigned a parameter?

when you AutoREST-Enable a table through object browser> click table> REST tab, you will get a RESTful URI. If you then build a web source using that RESTful URI, you will get five operations - GET with a dot as URL pattern and GET, PUT, POST and DELETE operations with URL pattern has the value of :deptno. When you build a report with form on that web source you will find that all database operations work well, you can insert, update and delete through the form, and you can run the report to get all rows in the table. I need to know how the process work in the background? How the automatic row processing process knows which operation and handler to use? I know that Interactive Reports for example looks for the operation that have "Fetch Rows" it's database operation. So, I assumed that the Form's automatic row processing looks up for the Web source's operation with the database operation that relates to the process to be executed. For example, (correct me if I'm wrong) when clicking CREATE button, it denotes that an Insert process will happen, so, it will search for the web source's operation with the database operation "insert row", then it will find the handler that relates to the HTTP method attribute's value "POST". And the same goes for UPDATE and DELETE. I want to know if I am getting it right and I need to know how the URL Pattern gets it's argument for :deptno?