1. http://initd.org/psycopg/docs/index.html
2. Microsoft SQL documentation. https://docs.microsoft.com/en-us/sql/
3. Postgresql. https://www.postgresql.org
4. Arni, F., Ong, K., Tsur, S., Wang, H., Zaniolo, C.: The deductive database system LDL++. TPLP 3(1) (2003)
5. Bishop, C.M.: Pattern Recognition and Machine Learning. Information Science and Statistics, 5th edn. Springer, Heidelberg (2007)