In this course you will first learn about entity-relationship diagrams and the basic concepts associated with the relational database model, including the canonical means of interacting with relational databases using queries written in Structured Query Language (SQL). You will learn how to connect the production-quality PostgreSQL database to a web application. Next we will cover a data access topic, namely object-relational mapping. This is used to convert data between incompatible type systems, in our case, between object-oriented data models in a web application and a relational database. You will learn how the Active Record Design Pattern is used to solve the object-relational mapping problem, and you will use it in a web application. Finally, you will learn how to connect a number of NoSQL databases to a web application, including NoSQL databases deployed as cloud services.