Expand your thinking in the abstract about what a database is. As 71104 mentions, a file system is also a database. What you are thinking of as "a database" is really a specific type of key-value store that is located on disk. But the fact most DBs are on disk has nothing to do with the concept itself.
Expand your thinking in the abstract about what a database is. As 71104 mentions, a file system is also a database. What you are thinking of as "a database" is really a specific type of key-value store that is located on disk. But the fact most DBs are on disk has nothing to do with the concept itself.