This book is based on a Postgraduate thesis at University of Hertfordshire, United Kingdom. This book investigates the performance (in terms of speed (runtime) and memory usage) of three Database Management Systems (DBMSs) i-e Object Relational (PostgreSQL), Relational (SQL) and Non-relational/NoSQL (MongoDB) Databases using "Airline Information System" case study. This report aims to analyze and compare three databases and to address the research question whether one performs better than the other and are there any significant differences in their performance. By analysis and investigation, the conclusion of the report is based on the fact that "MongoDB is fastest Database in performance (in terms of speed (runtime) and memory usage). On the other hand, SQL Database is slowest in terms of speed (runtime) and PostgreSQL Database is worst in memory consumption".