Introducing the DMSII Client
This chapter explains what the Databridge DMSII Client is, how it works, and the different components of Databridge.
The DMSII Client is a mainframe program that works with the Databridge host software to replicate (clone and then update) a DMSII database as another DMSII database. Updates to the client database occur as DMSII audit becomes available.
DMSII Client runs on all Unisys MCP-hosted mainframes.
The following diagram shows how the DMSII Client works:
The DMSII Client calls Databridge Server to clone a specified database.
Databridge Server calls the Databridge Engine to clone the specified DMSII database.
The Engine accesses the specified DMSII database via the DMSII Accessroutines.
Databridge Server receives extracted records from the Engine and calls the filter in Databridge Support.
Databridge Server sends records that satisfy the filter to the DMSII Client, which stores them.
Databridge Server calls the Engine to retrieve updates that occurred during the extraction.
The Engine reads the audit trail and sends the information to the Databridge Server, which calls the filter in Databridge Support.
Databridge Server sends the changed information from the audit file to the DMSII Client.
Understanding the Databridge Components
Each component of the previous diagram is explained in this section.
DMSII Access routines
The Access routines program is a DMSII utility that controls access to the database, reads and writes records, and creates the audit trail.
The audit trail contains all of the audit files generated for a database. The audit trail consists of audit files named as follows:
where databasenameis the name of the DMSII database, AUDIT is a literal, and nnnnis the audit file number (AFN), a number between 1 and 9999. For example, if you have a database named BANKDB, an audit file would be named similar to the following:
One of the primary reasons to replicate a DMSII database is to provide data to end users with minimum impact on host resources. Therefore, the data you replicate should be the data that end users will request most often. Most sites do not clone entire DMSII databases.
The Databridge Engine (DBEngine) is the main part of the Databridge replication software, which is explained in the Databridge Host Administrator's Guide. DBEngine is a host system library that retrieves structural information, layout information, and data from the DMSII database and passes the information to the Server Accessory.
The Databridge Support Library provides filtering and translation to the Server Accessory (as well as other Databridge Accessories). Once the Server Accessory receives data from DBEngine, it calls the Support Library to determine if the data should be replicated, and if so, the Server Accessory passes the data to the Support Library for formatting. In brief, the Support Library offers the following to the DMSII Client:
Virtual data sets
Virtual data sets appear as normal data sets to the Server Accessory and the DMSII Client, even though they do not actually exist in the DMSII database.
Data set filtering
For a complete explanation of data set, column, and row filtering, see the Databridge Host Administrator's Guide.
The Databridge Server (also referred to as DBServer) provides communications between the DMSII Client and DBEngine on the host. The Databridge Server calls all DBEngine functions for the DMSII Client. In general, Databridge Server responsibilities include the following:
Communicating with the DMSII Client. If you configure the auto connect feature in both Server Accessory and the DMSII Client, Server Accessory initiates communication with the DMSII Client when audit files become available. If you do not use the auto connect feature, Server Accessory waits until it is called by the DMSII Client.
Sending replicated DMSII data from DBEngine to the DMSII Client.
Sending DMSII database layout information from DBEngine to the DMSII Client.
Frequently, you can enhance performance by having the DMSII Client communicate with Databridge Enterprise Server instead of the Server Accessory. To configure this, in the DMSII Client parameter file, enter the IP address of Enterprise Server instead of the Server Accessory.
DMSII Client Support for DMSII Structure Types
The DMSII Client supports data sets, remaps, and logical databases. Data sets in the client database will have additional data items that do not appear in the primary database. These data items make it easier to locate records during tracking.
The DMSII Client makes embedded data sets disjoint in the client database. Consequently, application programs designed for the primary database may need to be modified in order to compile and run properly against the client database.
The DMSII Client supports all DMSII data set structure types except for the following.
Data sets embedded within an ORDERED or COMPACT data set
Embedded data sets if INDEPENDENTTRANS is reset
For information on DMSII structure types supported by Databridge Clients, see the Databridge Client Administrator's Guide.
The DMSII Client supports all types of DMSII data items except for the following:
Understanding How the DMSII Client Works
Following is a simplified description of how the DMSII Client works. This description starts after all of the necessary Databridge database replication software and DMSII Client components are correctly installed and configured.
Run the DMSII Client WFL.
The DMSII Client contacts the Server Accessory for required database information to create the DASDL code that it then compiles as the client database. After this, the DMSII Client sends a request for data to the Server Accessory.
The Server Accessory initiates DBEngine to extract data from the specified database.
The Server Accessory then sends the database information to the DMSII Client.
The DMSII Client populates the client database and then either waits for additional audit information or terminates.
If the DMSII Client waits for additional audit information, it periodically contacts the Server Accessory to see if updates are available.
If the DMSII Client terminates and it is registered for auto connect requests, the Server Accessory will initiate the DMSII Client when additional audit information becomes available.
As audit becomes available, the Server Accessory uses DBEngine to retrieve the after-images of modified records, which it then sends to the DMSII Client.
The DMSII Client updates the client database with the new information and then either waits for additional audit information or terminates.