The topic of this thesis is object-relational databases. The thesis is divided into six chapters. The first chapter covers the basics of databases in general. At the end of the first chapter, we describe the data modeling process, which we will refer to for each database type. In the second chapter, we describe the relational databases, the basic terms associated with them, and then we describe the entity-relationship model (ER model) in detail. The first chapter concludes with the relational model, the characteristics of which are described. In the third chapter, for better understanding, we first list the features of object-oriented programming. Next, we describe the UML class diagram and, using the same principle as in the previous chapter, we describe the object data model. The fourth chapter is a comparison of relational and object-oriented databases. We highlight their advantages and disadvantages. In the fifth chapter, we describe an object-relational database. It was created as a com- promise between relational and object-oriented databases and thus has the characteristics of the two previously described data models. The thesis concludes with the sixth chapter, which presents a case study of the modeling and testing of an object-relational database.