Ultimate Debian Database (UDD) gathers a lot of data about various aspects of Debian in a single SQL database. It allows users to easily access and combine all this data.
You can have a look at the UDD Schema.
More information about UDD is available at wiki.debian.org/UltimateDebianDatabase.
Some example queries are provided as CGI scripts, to make it easy for everyone to run them. You can browse them or view the source code.
If you want to know when UDD is being updated, you can check the crontab file. The timestamps table can tell you when a data source was last updated.
A full dump of the database, generated every two days, is also available. Be careful, it's quite big (400 MB gzipped, and growing).
If you want to reference UDD, please link to udd.debian.org/ and (in publications) use the following citation:
@InProceedings{udd-msr10, author = "Lucas Nussbaum and Stefano Zacchiroli", title = "The Ultimate Debian Database: Consolidating Bazaar Metadata for Quality Assurance and Data Mining", booktitle = {7th IEEE Working Conference on Mining Software Repositories (MSR'2010)}, address = "Cape Town, South Africa", year = "2010" }
Even if its main goal was not to serve as a scientific resarch tool, UDD was already featured in two publications: