The Advanced Peer-to-Peer Networking® (APPN) support of an iSeries™ server can be used to allow DDM access to systems not directly connected to the local server.
Figure 1 in Example: Use the basic concepts of DDM in an APPC network shows a program on the Chicago server accessing a file on the New York server. Although the servers are shown as directly connected, the same DDM concepts apply if the network is configured as shown in the preceding figure. When the DDM file CUST021 in the figure is opened on the Chicago server, the APPN support finds the remote location named NEWYORK, determines the optimal path through the network, and establishes a DDM conversation with that location. Although there might be several other servers (network nodes) forwarding the data between CHICAGO and NEWYORK, the source DDM and target DDM function as if there were a direct connection between these two servers.
If the file CUSTMAST were moved from NEWYORK to some other server in the network (for example, DALLAS), then in this example, the DDM file at CHICAGO needs to be changed. The remote location name would be changed from NEWYORK to DALLAS. If a large number of servers in the network refer to the file CUSTMAST, then movement of the file results in a change to the DDM file at each of these servers. By using the iSeries capability to have multiple local location names, maintenance of these files is reduced.
In the preceding figure, the server NEWYORK can be given two local location names, NEWYORK and FILELOC. The DDM file at CHICAGO uses FILELOC as the remote location name. When access to file CUSTMAST is required, APPN finds the location FILELOC in the system named NEWYORK, and the DDM conversation is established as before.
If the file CUSTMAST is now moved from NEWYORK to DALLAS, the user at NEWYORK deletes the local location FILELOC from his server, and it is added to the server at DALLAS. This is done by using the APPN local location list. When the program in CHICAGO now attempts to access the file CUSTMAST, the APPN support finds the remote location FILELOC at the server in Dallas, and the DDM conversation is established to that server. The movement of CUSTMAST did not result in a change to the DDM file at CHICAGO.
This example shows the concept of multiple local locations and how reduced maintenance results when files are moved from one server to another. The example is not intended to suggest that a unique location name should be used for every file accessed through DDM. The decision of which files should be associated with separate local locations should be based on such factors as the movement of these files and the number of remote servers accessing these files.