Basics
Services
A service as described by the Cambridge Dictionary, by taking one of its meanings:
service: a system or organization that provides something important that the public needs.
This meaning is also very accurate for the computing world. Moreover, a service will not necessarily only be consumed by people, but could also be consumed by other systems.
Servers
A server, as described by the Wikipedia:
A server is a computer program or a device that provides functionality for other programs or devices, called "clients".
It goes further, and also expand to reach a service definition:
Servers can provide various functionalities, often called "services", such as sharing data or resources among multiple clients, or performing computation for a client.
Processes
A process, as described by the Wikipedia:
A process is the instance of a computer program that is being executed by one or many threads. It contains the program code and its activity.
This definition is very tied to what we know about Operating Systems,
by referring to the thread
term, but you get the idea.
Application
An application, again, as described by the Wikipedia:
Application software [...] is a program or group of programs designed for end users.
And system software:
System software is software designed to provide a platform for other software.
Common ground
As developers, we create programs; they can be either application software or system software. These programs serve a purpose, whether it is for end users directly, or for other systems to consume.
Application software usually is meant to be consumed directly by end users, and so, interaction with the system will be UX driven, no matter what kind of UX (e.g. terminal, graphical...)
System software, however, is going to be consumed by other software, and as such, this creates friction on both systems. We can ask ourselves some questions at this point:
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How can both evolve and still make sure that they are complying with the contract they signed?
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What happens to one service if the other is not responsive, and the former depends on the latter?
We will explore this and other complexities throughout this book.