Going through my old notebooks and other material to get ready for a talk at the Security Onion Conference on Sep 11, I found an early description of the connection record format I was using in my NSM software. I would tweak it a little bit by the time I finished my Master's Thesis 6 months later, but this page pretty much captured most of it.
If you look at my notes (click on the image to get a larger version, or save to local disk), you will see that it is pretty much the same as session logs from many of today's NetFlow-like systems: connection channel (address and ports), protocol identifier, start & stop times, number of packets and bytes in each direction.
On one hand, it feels kind of nice that my log format is still essentially being used today. On the other hand, it saddens me that so many of us (including me) are still analyzing log data designed almost a quarter century ago.