Acyclic-graph directories
An acyclic graph permits directories to have shared subdirectories and files. The similar file or subdirectory may be in two dissimilar directories. A shared file is not the similar as two copies of the file. With the shared file, only one definite file exists, so any changes made by single person are immediately visible to other. Shared files and subdirectories can be executed in several ways. In UNIX shared files are executed by create a new directory entry known as a link. A link is effectively a pointer to another file or subdirectory.