The OGC WMS specification offers a standard client-server
interaction protocol that each map server implements as a
common interface for accepting requests and returning
responses. The same client is able to access to all available
OGC web map servers over the Internet. The client through the
common interface accesses each map server. In a distributed
OGC WMS, a WMS server can also run as a WMS client that
requests capabilities and maps from other WMS servers