A datagroup is defined in which type of file?

A datagroup is defined in a model file because the model file serves as the central configuration point in Looker, where the connections to the data sources and the data relationships are established. It allows developers to define how data is fetched and processed, including the use of datagroups, which are important for managing data freshness and caching strategies.

Datagroups specifically control how often Looker refreshes the data in the cache based on defined criteria, making them crucial for ensuring that users work with up-to-date information. By placing datagroup definitions in the model file, developers can easily manage and organize how different datasets are handled across various views and explores, thus maintaining a cohesive data architecture.

Other file types, such as view files, explores files, or dashboard files, serve different purposes. View files are where the structure of dimensions and measures is defined, explores files define how users can query the data, and dashboard files are merely for visualization and layout of data insights, without any data management functionality. Therefore, placing datagroup definitions in the model file aligns with Looker's architecture and best practices for data management.