I have inherited some pretty crappy requirements and diagrams, and before I start proposing changes, want to be sure that I understand things properly?!
My question revolves around “Services” and “Interfaces”. (Not sure if this is the right website to ask these questions?!)
To me, a SERVICE is like a mini program which takes inputs, performs a series of actions, and then spits out a result.
An INTERFACE is simply a definition of what constitutes an INPUT and an OUTPUT (e.g. Data Fields, Size, Type, etc.)
Different Systems and Services talk to one another via INTERFACES, but it is the Systems/Services that actually do things!
When a diagram is trying to show how a series of Systems talk to one another to produce some end results, I would think that you would want to show each SERVICE along with the DATA that is flowing back and forth between the Systems/Services…
For instance, an E-commerce System might take “Order Information” and pass it to the Inventory “service” to see if a product can offered.
The action is the System talking to the Service, and not necessarily what format constitutes the INs and OUTs, if you follow me?
The requirements that I inherited seem to put all of the emphasis on the INTERFACES and making it sound like the INTERFACES are doing all of the work when that is totally not the case - as far as I know?!
For instance, the person wrote…
If the person is qualified, the interface will automatically request and receive a list of available plans…
Interface-7 will perform the necessary data transformations and then call Interface-3, and Interface-3 will have a secure VPN connection to System-B to make the request.
That totally sounds wrong to me!!! 
Can someone help me get a better handle of all of this?!
Thanks,
Debbie