Some file systems permit a hierarchical directory structure of virtually unlimited depth. Some file systems are flat and permit no directory structure at all. Some file systems permit directories but only up to a maximum depth. Other file systems permit directories but the directory structure is fixed or read-only, i.e., the creation or deletion of directories is not permitted. This is to be distinguished from a read-only file system in which neither files nor directories may be created or removed, and in which file data may neither be added nor modified. In a file system where the directory structure is read-only, files may be created and removed from directories but the directory structure remains static. Modification of the directory structure is an operation beyond the semantics of the file system. Some FTAM File Stores have such static directory structures.
In a network environment, a client may have several remote file systems attached from different servers and these file systems may vary in their directory manipulation capabilities. An application should be able to know the structure semantics of all accessible directories.