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Successful VS/PC exchanges require knowing your files inside and out

From "VS Workshop",  Access to Wang, December 1991
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A large number of VS users have found it helpful - sometimes even vital - to move information between VS and PC applications. Yet many Wang users do not understand how the internal file structures of the two systems compare and, therefore, do not make maximum use of the informational exchange. Without the time to experiment, they often settle for less-than-ideal solutions rather than wrestling the problem to the ground.

As one who views information exchange between unlike systems as the ultimate hacking challenge, I have pursued opportunities to exchange formats whenever there was need. The result of this experimentation has been a greater appreciation of exchange issues and the ability to better meet the requirements of new system conversions as they occur.

This month we can bring the file transfer laboratory to your shop. The only prerequisites are some sort of file transfer software, a number of VS and PC files of all types to use for tests, and an interest in the physical and logical properties of files. The file transfers can be performed by any transfer software, including 2110 emulation software or products that make use of a Wang WLOC (Wang Local Office Connection) terminal emulation board in a PC.

Glossary

First, some file lexicon is in order. The definition of a text file is probably one of the most debated terms in this profession. As used here, a text file is a consecutive file with records delimited by LINE FEED/CARRIAGE RETURN combinations. The text itself must be displayable characters normally found on a typewriter keyboard (e.g. above X'1F and below X'7F) plus a handful of control characters. Valid control characters include FORM FEED (X'0C), LINE FEED (X'0D), CARRIAGE RETURN (X'0A), TAB (X'09), and END OF FILE (X'1A).

File access methods are the means available to access field information. Sequential files on either system can be accessed in record order or randomly by record number. Sequential or random access by a field value is supported by indexed and alternate-indexed files on the VS. There is no direct equivalent in the PC world; instead, a number of indexed file access methods are supported by specific languages, compilers, and data base systems. Meaningful exchange of indexed information requires programming effort at either or both ends to convert the field data to a common format (typically text) and provide the indexed fields separately.

File Taxonomy

Proper file exchange depends on an understanding of the physical and logical characteristics of the VS and PC environments. File characteristics can be grouped into three categories: Physical, Logical, and Other.

Physical characteristics are the dimensions of the file, including the following:

Logical characteristics refer to internal record structure and its use. These parameters include:

Other VS file characteristics include create date, modification date, expiration date, file class, Access Control List information, physical disk location, and special access privileges. Other PC file characteristics include create date, create time, physical locations, and file attributes (system, hidden, archive, read only). These parameters are of little interest in file transfers except where they might inhibit access.

Transferring VS files to the PC

The VS file type determines the method used in transferring files to the PC. Some possible approaches include the following:

Transferring PC files to the VS

Because PC files do not have many external clues as to their format, transferring PC files to the VS requires careful use of file naming conventions and a greater understanding of the internal contents of the file. Some practical uses include:

Other issues

Other issues in file exchange with PCs include the use of the tab character (X'09) to replace leading spaces in PC files, the presence of trailing spaces in VS files, and end-of-file markers in PC files. Some PC programs use tabs to replace leading characters and reduce the size of files. Normally these tabs are set at increments of eight characters - an ASCII standard. VS files are also expanded to their maximum length during a READ operation, possibly introducing trailing space characters in the PC output. Finally, there appears to be a division of opinion in the PC world whether the MS-DOS END OF FILE marker should be used. Better file transfer software gives you control of all of these factors. (For a utility to remove trailing spaces, see "To Any Length", Access to Wang, October 1989, p. 45.)

Obviously, there is a large amount of information that must be exchanged about the format of unlike files to make effective use of data in both environments. Please share any ideas you have for making this process more reliable.


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Copyright © 1991 Dennis S. Barnes
Reprints of this article are permitted without notification if the source of the information is clearly identified