data_jd

I suspect the J package Jd is probably the most non-trivial public codebase. I don’t love the coding style (functions are long and scripted) and it doesn’t make use of newer lambda functions (“direct definitions”) which are easier to read. https://github.com/jsoftware/data_jd

I found this license for jd itself. It is free only for non-commercial use: https://github.com/jsoftware/data_jd/blob/master/doc/License... The link you mentioned only applies to the jsource folder: the jengine code.

Here's one of the more central files that ties into how a Jd database is laid out: https://github.com/jsoftware/data_jd/blob/master/base/common... Not that I claim anyone in particular can read it of course. Jd uses a hierarchy of folder, database, table, column that's handled with an object system to share code between them. A folder is just a place to put databases and hardly needs to add anything, while the other levels have a lot of extra functionality. As an inverted database, Jd stores each column in a file, and accesses it using memory mapping. https://github.com/jsoftware/data_jd/blob/master/base/folder... https://github.com/jsoftware/data_jd/blob/master/base/table.... (I designed this system when I did some of the early work to turn JDB into Jd as a summer intern)

J is fully opensource: https://github.com/jsoftware/jsource Most of jd's source is publicly available: https://github.com/jsoftware/data_jd

An example J file because this link doesn't say much: https://github.com/jsoftware/data_jd/blob/master/csv/csv.ijs