File system details

By design, the COBOL runtime will interface with any file system that stores and retrieves record buffers, taking advantage of indexes over these record buffers when requested. That access method mirrors exactly the architecture of FairCom’s c-treeACE ISAM interface. Therefore it was natural to implement the required interface and give COBOL applications access to c-tree. The c-treeACE for COBOL file system links directly into the COBOL runtime, giving existing applications immediate access to c-tree without any need to recompile the application. The COBOL runtime configuration, together with a c-treeACE for COBOL configuration file, allows the user to map files into the c-treeACE file system, activate specific FairCom features like the transaction processing, remap COBOL application paths etc.

By design the c-treeACE for COBOL interface takes advantage of the c-treeACE Engine and all the inherent server features. In a client/server architecture, a very important factor to consider is the time spent during communication between client and server, particularly with file systems where direct disk access does not exist. With this in mind, FairCom's engineers customized a special edition of the c-treeACE Engine, c-treeACE for COBOL, in order to bundle into the server the functionality required from the file system by the COBOL runtime, making the code linked into the runtime just a thin client sending requests directly to the server. This significantly reduces the network traffic and the time spent in communication. It is also possible to use a non-customized c-treeACE Engine, in which case the logic uses the standard c-treeACE client approach where any of the interfaces provided to the COBOL runtime use c-treeACE ISAM calls to the server (with the effect that one COBOL operation may result in multiple calls to the server).

Due to the client/server architecture of c-treeACE for COBOL, some file maintenance operations that COBOL programmers are used to performing from COBOL code—like copying a file from one location to another—could be difficult, if not impossible since the COBOL application may be running on a remote machine and have access to the remote file system only through the c-treeACE Engine. In order to provide these types of maintenance related operations, FairCom introduced a brand new concept, the Cobol Command Channel.

COBOL Command Channel

The Cobol Command channel is a mechanism to send remote commands (from a predefined list) to the server in order to execute maintenance operation. The idea is that there is a pre-defined file that a COBOL program can open (configurable in the c-treeACE for COBOL configuration file), a write to this file is the way to send a command to execute, and reads from the file is the way of getting the command output.