What is the difference between an API , framework and middleware?

Question

Just Randomly got this question in my head! Whats the difference between API , Framework and middleware? Essentially all of them provide abstract low level services to apps. In

Answer 1

An API is an interface to a programming library (or libraries). It doesn't impose on you a way of doing anything. E.g. OpenGL doesn't restrict what you can do with it.

A framework supplies you with part finished solution to a problem. You fill in the blanks to make what you want. This might accelerate what you are doing, but you are also limited by the limitations of the framework, e.g. design, performance, functionality. -- E.g. MFC provided a way of creating UIs. It supported dialogs well, but not forms, and things like docking were limited and contained bugs. Windows Forms is a much more capable framework (from the architect of Borland Delphi!) which is better in every way: design, flexiblitiy, tools, etc. Frameworks are great until they don't do something you want them to do and then you may lose most of the time you gained trying to work around them.

Middleware is a vertical slice. If you think of software as layered (E.g. OS, hardware abstractions, utility libraries, etc), middleware incorporartes many of these layers vertically. It provides a full, or partial, solution to an area within your application. E.g. a brokered messaging system, or a rendering library/engine. Middleware supplies more than just the basic library, it also supplies associated tools like logging, debugging and performance measurement. One thing you have to be careful about when using middleware is the DRY principle. Because middleware is vertical system, it may compete or duplicate other parts of your application.