Chapter 4. Support the User's Mental Model
When we consider how to organize papers, we may think of filing cabinets. We fill filing cabinets with hanging folders, and fill those with manila folders, each with its own stack of files. We use labeling systems to help us remember what each folder contains.
In modern operating systems, we can glance around a virtual desktop full of folders (represented by icons), spot the one we need, open it up, and scan its contents to find the file we need.
In reality, though, computers use addresses to tell them where each specific bit and byte is stored. The addresses on the hard disk don't need to correspond to a filing systemin fact, two files stored in the same folder do not necessarily exist in consecutive spaces on the hard drive.
As another example, when we think about throwing something away, we usually think of trash cans. Trash cans sit in every room in our houses and offices, and do nothing but give us a place to toss items we no longer need.
Today, instead of entering obscure terminology into a command-line tool to delete a filewhich is how it used to be donewe throw it away. We drag a file icon to another icon shaped like a trash can or recycling bin. The visual metaphor has replaced the typed command, and deleting files has come to mean throwing them away.
Much like throwing something away in real life, the trash metaphor used by Mac OS X lets us visualize the removal of an item in a way that supports our mental model.
In actuality, the metaphor of throwing something away bears no resemblance to deleting a file from a computer. But which makes more sense to you? The act of throwing a file in the trash can, or deleting an address from the hard drive's index so the storage space can be overwritten the next time the computer needs to save to the hard drive?
The useful, concrete mental metaphor has effectively replaced the reality of what occursand no one cares! The metaphor works, and is much simpler than the reality.
In both of these cases, users have been given visual metaphors that adhere more closely to our knowledge of the world outside of our computers. Trash cans are used for trash, and filing cabinets are used for organizing files. This is how we do things in real life, and now this is (more or less) how we do things on a computer. What we believe about what happens has nothing to do with the reality of what happens on the computer. But we rely on our real-world experiences to help us assimilate and understand.