>   Each      is stored under a set of 4 successive directories called repository.

Example of a repository:

This repository is written:

dpi.inpe.br/ronei/1996/11.20.18.56

When convenient, a repository is represented like a single directory.

Example of a repository in its simplified representation:   

>   A set of repositories under the same directory is called a local collection. The directory is named col.

Example of a local collection with two repositories: