In a database management system (DBMS), data models are used to describe how the logical structure of a database is modeled. Data models are fundamental entities that introduce abstraction in a DBMS. They define how data is connected to each other and how they are processed and stored inside the system. A data model gives us an idea of how the final system will look like after its complete implementation. It defines the data elements and the relationships between the data elements.

There are several types of data models used for understanding the structure of the database. The most widely used model is the Relational model, which uses tables to represent data and in-between relationships. Other types of data models include the Hierarchical Model, Network Model, Entity-Relationship Model, Object-Oriented Data Model, Object-Relational Data Model, Flat Data Model, Semi-Structured Data Model, Associative Data Model, and Context Data Model.

Each data model has its own set of symbols and language to represent the information so that members of an organization can communicate and understand it. Data models are used to show how data is stored, connected, accessed, and updated in the database management system. They contain relationships between tables that address cardinality and nullability of the relationships.

In summary, data models in DBMS are tools developed to summarize the description of the database. They provide a transparent picture of data which helps in creating an actual database. Data models contain relationships between tables that address cardinality and nullability of the relationships. They are used to show how data is stored, connected, accessed, and updated in the database management system.