Configuration files managed by NIS are converted into keyword value
pair tables called maps.
NIS maps are constructed from DBM database files.
Under DBM, a database consists of a set of keys and associated values
organised in a table with fast lookup capabilities.
NIS map structure - Each NIS map comprises of two files : a hash-table
accessed bitmap of indices and a data file. The index file has the
.dir extension and the data file uses .pag. So a database called addresses
would be stored in