Charles asked "A buddy of mine asked me if I knew anything about Model 204. I've never run across it, but it sure smells like a cousin of the multi-value, or perhaps XML, model. Anyone know anything?"
I studied Model 204 in 1975 in my "Comparative Database" class. It was a new approach to handling data for it could handle both sequential and random reads/writes. Having mastered INDEXED SEQUENTIAL, it allowed for immediate placement into a sequential file, whereby you could continue to read and process sequentially. This was a boon for accounting and scientific applications alike for you didn't have to read thru the whole file. (Whooo Whooo Whooo). Eventually, I programmed in it for about a year in my work study program for NOAA (National Oceanic and Atmospheric Administration). The project was super cool for they were flying planes thru heavily air polluted areas with lasers mounted to the ends of the wings. The lasers had light sensors that picked up the reflection of the laser light off of the particulates in the air. We took the information from magnetic tape and loaded the values into massive files used to track and estimate the dissipation of the particulates. I never considered Model 204 as a multi-value variant due to it's rigid (inflexible) structure. MV's strength lies in the ability of variable length fields and to change any field to a MV field. As a strong competitor to IMS and CICS, it did gain some hefty clients during it's time, however was completely eclipsed by the high availability strengths. An example of the strength of CICS is it's ability to change stuff within the core run engine without taking the DB down. Yep, you discover a bug in the query function in the run engine, and you can replace the code section for the query function on the fly to fix it!!! This lead to many shops moving away from Model 204 to IMS or CICS. A long time ago, there were people who compared COBOL & Model 204 data structures to those of the MV world. When defining the data structure in COBOL & Model 204, there is an OCCURs clause that allows a field to be repeated (at a fixed length) for "X" number of occurrences. While this is really stretching the definition, it did allow for fields to be repeated up to a predefined number of values. I almost laugh ever time I read about the XML capability of any database. All it means is that it "Can" map to a logical / physical data store. But believe me, if you have to restrict the length of a field, and it can have only so many values before it blows up, is not really XML at all. Please remember that when IBM embraced XML, U2 had the fastest, full function system in all of IBM. UniData then developed COBOL Direct Connect (CDC) to solve the reporting / data store problem. CDC is still available within UniData. We need to sell that more. Steve Stephen M. O'Neal U2 Lab Services Sales Specialist Information Management, IBM Software Group ------- u2-users mailing list u2-users@listserver.u2ug.org To unsubscribe please visit http://listserver.u2ug.org/
