In which of the following systems is the data usually organized in a relational model?

The correct answer is Database Management Systems (DBMS). In a relational model, data is organized into tables (or relations), where each table consists of rows and columns. This structure allows for the establishment of relationships between different tables through the use of keys, enabling efficient data retrieval and manipulation.

Database Management Systems are specifically designed to manage large quantities of structured data, offering functionalities that include querying, updating, and ensuring data integrity and security. They utilize Structured Query Language (SQL) to enable users to communicate with the database for operations such as retrieving and modifying data.

In contrast, file management systems typically do not organize data in this structured way and may simply manage individual files without relational capabilities. Transaction processing systems focus on the execution of transactions and ensuring data integrity over individual operations but do not inherently organize data in a relational model. Content management systems are designed for the creation, management, and storage of digital content, which may not follow a strictly relational format either, as they often handle unstructured or semi-structured data.