pq
pq is the worlds first Implicit-Relational Database (IRDB). Unlike in more conventional relational databases, the work of figuring out which data elements join with which in a query is done by the server, rather than by the client. Clients in this model are far simpler, making them easier to develop quickly and less likely to have bugs.
The system also has a novel, modular structure internally. Some modules perform intermediate processing on queries or their results, synthesizing some values from others or giving programmatically-defined answers, while others refer to other data sources for their information, such as local files, other pq servers, or other types of database servers.
pq started life at AT&T where it was used for the internal corporate directory. It evolved from a very rigid system into a modular, distributed database capable of pulling data from a wide variety of resources. It is still in use at some of the AT&T spin-off companies, where it serves as a simpler, portable front end to a collection of HR and accounting systems.
This distribution of pq is based on version 4 of the POST group's pq, written by Michael Baldwin while in Bell Labs. Version 4 was the first version to gain significant use outside the POST group, and in 2001 was released as open-source (see the additional software collection for Plan 9, or /n/sources/extra/pq.tgz on Plan 9).
Since its open-source release, pq has been used in several commercial systems, each time extended to the needs at hand. Unfortunately, all these extensions are in companies with no interest in releasing them. Each time that happens, the next party to come along misses out on all the good work that's been done. This project aims to prevent that from happening in the future.
Work is ongoing. We've got a few modules in place which extend the query capabilities of the system, and we've done a lot of work on documentation and packaging to make it easier for folks new to the system. We're currently working with the maintainers at Bell Labs on determining the best distribution system.