What does an Entity-Relationship (ER) diagram depict?

An Entity-Relationship (ER) diagram serves as a powerful tool in database modeling, illustrating the entities involved in a system, along with their attributes and the relationships between them. This visual representation helps in understanding how different data elements interact with one another within the context of the database.

By identifying entities—such as people, places, or things—and their relationships, an ER diagram allows designers to construct a clear blueprint of the data structure before implementation. This aids in ensuring that the database is organized in a way that supports the necessary data requirements of a system, facilitating efficient data retrieval and manipulation.

The other options do not accurately capture the purpose or function of an ER diagram. For instance, while the first option mentions the logical flow of data, it's more focused on processes rather than the static structure of entities and their connections. The third option, which refers to a layout design for database tables, is related but does not specifically encompass the conceptual modeling aspect that ER diagrams provide. Lastly, the fourth option describes a graphical user interface, which deals with how users interact with a database rather than the underlying relationships and structure depicted in an ER diagram.