To split or not to split? Tools little help answering - includes related article on Cooperative Solutions Inc - Client/Server Computing: Development Tool Status Report - tutorial

Software Magazine, Feb, 1991 by Paul Korzeniowski

Often, decisions are not as clear-cut. As you start to divide functions between servers and client workstations, delimiters become real fuzzy real quick," noted Michael Mahez, director of research at Caseworks Inc., an Atlanta software supplier.

As dividing lines blur, users need help to determine if designs are feasible. Easel's Canestraro said no tools are available "to help users understand how their client/server applications will function once they are installed."

In many instances, the application again establishes proper boundaries. For instance, customer credit card information could be stored on a client workstation and sent to a server each night. Or the information could be immediately shipped to a server for processing.

If information is stored on a client workstation, a customer could exceed his or her credit and no one would know until the following morning. By constantly updating server information, corporations can prevent credit card fraud. For most mission-critical applications, corporations opt for the second approach. For example, Hills Arts and Entertainment Systems in Emeryville, Calif., sells software that theaters use to track ticket sales for various events. Dirk Epperson, vice president of research and development, said, "Obviously, a theater wants sales information stored in one database so customers don't buy seats that have already been sold."

Two years ago, the company decided to rewrite its applications, which ran on DEC VAX and PDP/11 computers. The finn chose a microcomputer LAN and Sybase's database management system as the foundation for the rewritten applications, scheduled to be completed in the first quarter. "Sybase's two-phase commitment ensured that the server would work with current information," Epperson explained.

A two-phase commitment means that information generated on a client workstation will not be acknowledged until it has been stored on a server. For instance, a ticket sale is recorded on a client workstation but is lost as it passes to a server. In many instances, the client workstation would log a completed sale even though the server never received the sales information. With the Sybase system, the client workstation would not be able to close out the sale until the server received the sales information. the information was lost, the client workstation would have to again generate it and send it to the server.

ENSURING DATA COMPATIBILITY

Another difficult issue is ensuring compatibility between client and server software. Vendors will claim that mainframe and LAN client information and applications are completely compatible, but that is not always the case," noted Bob Barr, manager of information resources at the South Carolina Tax Commission, Columbia, S.C.

Three years ago, the Tax Commission offloaded mainframe applications based on the CA/IDMS database management system from Computer Associates International Inc., Garden City, N.Y. "When we first installed the applications, we dealt with two vendors: One supplied the LAN software and the second sold the mainframe package," Barr explained. Luckily, Computer Associates purchased both companies, and has tailored the two packages so they are completely compatible."