GUI - Graphical User InterfaceAPI - Application Programming InterfaceIn short, a GUI is the user-facing side of a program, the part that a user (typically, human) interacts with, and controls the...
web service is like advanced Urls and API is Programmed Interface.
API contains classes and Interfaces just like a program.
A web service is a form of API (Application Programming Interface).
An...
An API is really no more than a set of method signatures and other information necessary to use a class or set of classes. The API is totally distinct from the implementation. For example, a number...
It's quite easy.
API 6A speaks about wellhead and x-mas tree equipment, API 6D speaks about pipeline valves.
If you are phisically looking to one valve, you can also understand if it belows to 6A...