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F.2.5 Acu4GL for DBMaker: Designating the Host File System

When your COBOL application opens an existing file, most file systems linked into the runtime will be searched for the named file. However, each time the COBOL application creates a new file, it needs to know which file system to use. You provide the name of the file system with one of two runtime configuration file variables; the first is:

     DEFAULT_HOST filesystem

This will designate the file system to be used for newly created files that are not individually assigned. For example,

     DEFAULT_HOST DBMAK

means that all new files will be DBMaker files unless otherwise specified by the second configuration variable, which is:

     filename_HOST filesystem

where filename is the file name, without any extension, named in the ASSIGN TO clause of your SELECT statement. This configuration variable is used to assign an individual data file to a different file system. Any file so assigned uses the designated file system, and not the one specified by DEFAULT_HOST. For example,

     myfile_HOST VISION

means that myfile will be under the Vision file system. The ability to designate a different file system for certain files enables you to tailor your application to a specific customer's needs or to implement an incremental conversion for a customer. With relational databases, this is particularly useful in that it allows you to tune an application for processing speed and resource requirements.

You can use these runtime configuration file entries in combination to assign your new files in a default with exceptions manner. For example, this set of entries:

     DEFAULT_HOST VISION
     afile_HOST DBMAK
     bfile_HOST DBMAK

means that all new files except afile and bfile will be assigned to Vision, and those two files will be assigned to DBMaker.

You can also change the values of these variables during program execution by including in your code:

SET ENVIRONMENT "filename_HOST" TO filesystem

or

SET ENVIRONMENT "DEFAULT_HOST" TO filesystem

This enables you to change file systems during the execution of your program. This is not the typical way to specify a file system; normally it is designated in the runtime configuration file and is not changed in the COBOL program.

Note: Acu4GL for DBMaker allows you to create an DBMaker table with an OPEN OUTPUT statement, just as you can create Vision indexed files. The DBMaker equivalent of a Vision file is a table, not a database. You must create a database for your DBMaker tables before you run the COBOL program that creates the tables, just as you must create a directory for your files before you run a COBOL program that creates Vision files.