Overview

ADDE (Abstract Data Distribution Environment) is the client/server mechanism for distributing data in McIDAS-X. In ADDE, an application sends a request for data through an API routine to a server. The server is the software running on a machine in a distributed system that stores data and supplies it to the client upon request.

What does a server do?

The server's job is to:

Interpret the data request from the client
Retrieve the requested data from disk
Arrange the data into the proper format for the client
Send the data back to the application

When the application reads the data sent from the server, the physical location of the original data and its stored format are transparent.

How many server categories does McIDAS-X have?

McIDAS-X has two server categories: primary and secondary.

Primary servers are started directly by the ADDE communications module, mcserv. They read the client request from stdin (standard input).
Secondary servers are started by primary servers. They don't read the client request from stdin, but rather from the server's argument list.

In short, a user enters a data request based on the ADDE group and descriptor name. mcserv starts the appropriate primary server based on the request type. The primary server extracts information about the requested dataset from the server mapping table, including the stored format of the data. If the stored data format is different from the standard McIDAS-X stored formats, the primary server starts a secondary server to convert the data to the format the client expects.