NetBase for MPE Reference Guide

Chapter 1
1-4
NetBase Shell
The NetBase shell is a set of procedures that install into the system libraries. These procedures
intercept TurboIMAGE and file system intrinsic calls. In fact, the NetBase shell procedures have
the same name as the MPE/iX procedures. This allows NetBase to trap the activity to files or
databases without having to make any changes to application programs. The NetBase shell traps
programmatic activity to files or databases. It does not intercept MPE commands such as BUILD,
RENAME or COPY. There is a special UDC that can be enabled for this. For more information on
this UDC, turn to Appendix A “Installation/Update Procedures”.
For example, when an application program passes a DBOPEN, it is intercepted by the NetBase shell.
The NetBase shell then does a lookup in the NetBase directory to check if this database is to be
shadowed or accessed on another system. If no directory entry exists for this database in the
NetBase directory, the NetBase shell passes the DBOPEN call to the real DBOPEN on the system for
processing. If a directory entry exists for the database to access it on a remote system via NFA, the
NetBase shell sets up the necessary processing to connect this user to the remote system.
Application
NetBase Shell
Operating System
Call to “DBOPEN”
NetBase DBOPEN
Internal NetBase
Processiing
MPE/ix DBOPEN
The NetBase shell does a lookup in the NetBase directory for every file and database open that
occurs on the system. If no directory entry exists, the request is passed to the MPE/iX operating
system. If an entry exists, the NetBase shell does the necessary processing to either shadow the file
or access it remotely, and then passes the request to MPE/iX.
The interception by the NetBase shell is completely independent of the NetBase background job.
Once the shell is installed into the system libraries, the interception begins. Remember that the
NetBase background job is used for transportation and communication.