At what stage and in what part of the system is data selection and processing performed?

Data selection and processing in the system are usually carried out at the business logic layer, which is located between the presentation layer (e.g., user interface) and the data access layer (e.g., database). In PHP applications, this is often implemented in controllers or services.

At this stage, the following occurs:

• retrieving data from the source (e.g., from a database);
• filtering and validating data;
• transforming data into the required format;
• applying business rules.

For example, in an MVC architecture, the controller receives a request, calls the model to fetch data, processes it, and passes it to the view for display.