The /.:/cdshostname_ch entry is the namespace entry for cdshostname's clearinghouse, where cdshostname is the name of the host machine on which a CDS server is installed.
A clearinghouse is the database managed by a CDS server; it is where CDS directory replicas are physically stored. For more information about clearinghouses, see the OSF DCE Administration Guide. All clearinghouse namespace entries reside at the cell root, and there must be at least one in a DCE cell. The first clearinghouse's name must be in the form shown in the figure, The Cell Namespace after Configuration, but additional clearinghouses can be named as desired.