Doesn't that just punt the question to, "what is a computational object"?
The fundamental abstraction/metaphor of the CLI is the file (especially in unix), where for a graphical system it is the "window". But the window has always been a weak metaphor. Windows are nothing like the thing outside the computer. Nobody understands them to be metaphors to physical windows. They are much closer to the computational object they represent (an area of i/o) than they are to a real window. Files on the other hand, are like their physical non computer counterparts. They are in fact much closer to real files than they are to a filesystem that's divided up into sectors or whatnot and distributed in the disk.
Does that mean from this definition, cli's are the metaphors and window systems are the abstraction?
A window is full of physical metaphors, like buttons, draggable handles/bars, tabs/paging.
But yes, it is also an abstraction of a set of related functions that manipulate or show data. It is even necessarily an abstraction of the computational objects it represents. But the sign(s) of the window points to physical/metaphorical objects.
Now the name "file" is also a metaphor. It represents (abstracts) a block of physical memory. But "file" is (or was) a sign for a physical thing made out of paper.
The metaphor of a file is on one hand useful, as it helps to understand physical memory as a set of objects we relate to in the outside world.
However it is also misleading: A real world file is typically immutable, to a high practical degree at least. We usually don't change files outside of correcting mistakes. We just add them and put a date. The file is first in "working" mode, then it is "done" quasi forever. To achieve the same with the computational object we need to impose constraints and/or discipline.
The fundamental abstraction/metaphor of the CLI is the file (especially in unix), where for a graphical system it is the "window". But the window has always been a weak metaphor. Windows are nothing like the thing outside the computer. Nobody understands them to be metaphors to physical windows. They are much closer to the computational object they represent (an area of i/o) than they are to a real window. Files on the other hand, are like their physical non computer counterparts. They are in fact much closer to real files than they are to a filesystem that's divided up into sectors or whatnot and distributed in the disk.
Does that mean from this definition, cli's are the metaphors and window systems are the abstraction?