Portable Database Management with /rdb
Now we look at a slightly more complex example: the generation of mailing labels. Assuming that stdin is an /rdb table with fields named Salut (Mr., Mrs., etc.), Fname, Lname, Address1, Address2 (sometimes blank), City, State and Zip, we create the script shown in Listing 3.
For each row in the table, this script creates a mailing label with either three or four lines (depending on whether or not the second address line was used). After adding columns to represent the lines in our final output, the compute command determines their contents. The resulting table is sorted by zip code so that the labels are grouped for bulk mailing purposes. The report command formats the output using the report.frm file shown here:
<Line1> <Line2> <Line3> <Line4>
This file is a very simple example of a report form file used by /rdb to generate reports. A field name within brackets indicates the substitution of the contents of the named field.
Other report file options are available as well, although we won't describe them here. One of the most significant options is the placement of output from shell commands. In this example, the output from report is a series of labels in a single column. This data is piped into pr which arranges it into two columns.
There are five access methods provided by /rdb: sequential (used by the above examples), record, binary, inverted and hashed. An index command is provided to build index files, and a search command is used to execute keyed retrievals.
A set of library functions, librdb.a, is provided for use by those who require access through C programs. Complete C source code for these functions is also included.
/rdb is a powerful but low cost package suitable for a large variety of database management tasks. It offers the following benefits:
Low cost: Only $149US for Linux, SCO and other Intel Unix implementations, $495US for RISC platforms.
Short learning curve: Users already familiar with Unix become proficient quickly.
Low Hardware Requirements: /rdb requires under 5MB of disc space to install. /rdb commands are compact since they function mostly as front ends for standard Unix tools. The mailing list application presented above is a “real world” program that was previously done using a dBase file. Since the dBase file used fixed-length fields, they contained a lot of trailing blanks which were eliminated when converted to an /rdb table. As a result, the /rdb table was roughly one third the size of the original dBase file.
Integrates well with other Unix commands: This point is illustrated in the web server log analysis example. One could easily create generic interface programs for other systems (including other databases) and using /rdb to provide data entry and validation on the input side and report generation on the output side.
Portability of data and code: This is becoming increasingly important as networked computing environments become more common.
The only disadvantage is that platform-independent systems generally run slower than those that are machine specific. Also, variable- length records tend to be more difficult to manage than fixed-length ones. Even so, /rdb performs well even with large databases (see Resources for pointers to demos available on the Web). Even in the extreme cases where a more traditional database system may be needed, /rdb can still be used as a front end as shown in Listing 2.
Finally, the economic considerations involved in the hardware independence versus performance tradeoff are clear. Hardware price/performance ratios are dropping rapidly while the cost of programmer time is constantly rising. This being the case, hardware independence is the uncontested winner.
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- KDE Reveals Plasma Mobile
- Huge Package Overhaul for Debian and Ubuntu
- The Controversy Behind Canonical's Intellectual Property Policy
- Home Automation with Raspberry Pi
- Shashlik - a Tasty New Android Simulator
- Embed Linux in Monitoring and Control Systems
- diff -u: What's New in Kernel Development
- General Relativity in Python