DATABASE CONVERSION AND TRANSFER

By William Holmes

Database conversion and transfer is mainly concerned with three issues: 1) conversion between different computers; 2) conversion between different software; and 3) transfer between different versions of the same software.

TRANSFER BETWEEN MACHINES

Transfer between machines has problems when the machines use different codes for storing data or when they have different operating systems. There are two different principal code schemes used by computers: EBCDIC and ASCII. These procedures differ in the way they store alphabetic characters, typographical characters, and control characters. They use the same procedure for numbers. If one has data in a raw text file that only contains numbers, direct transfer is possible. However, databases are not “raw text” files. They use special typographical and control characters. Thus, databases must be converted from EBCDIC to ASCII code schemes, or visa versa, when they are transferred between machines that use these different coding procedures. Mainframe IBM computers use EBCDIC coding. PCs and Apple use ASCII. Some software programs will automatically recognize whether a file is EBCDIC or ASCII and convert a file as necessary. To download a file from a mainframe to a PC may require saving it in a simpler form (such as comma delimited fields, CDF, sometimes called comma separated variables, CSV) to make conversion easier.

DIFFERENT SOFWARE

Information in a database may need to be transferred to spreadsheets, statistical analysis programs, word processing programs, or other database programs. Many programs have the capacity to read and files from a few other programs, but not all other programs. It is sometimes necessary to save a file, a query, or a report in a common form that can be read by another program, so that it can be transferred. Spreadsheet, HTML, RTF, and ASCII text are all formats that can be read by many other programs.

DIFFERENT VERSIONS

A special problem arises when database files are transferred between different versions of the same database program. Generally, one can go from an earlier to a later program without too many problems. They are said to be “forward compatible,” although some programs like Access require use of a conversion tool in Access to do this conversion.

Going from a later edition to an earlier edition is more difficult, because all the changes in the newer edition may alter the format of the database file. In such a case, it may be necessary to save the data in an earlier format of the program, so that it can be read by an earlier version of the program. Note, however, that this sometimes means losing features unique to the later program. One must be careful that data are not lost in the process.