Previously, we have learned how we can define our data model through the user interface (UI), such as creating new objects and new fields and linking them to each other by creating specific relationships.
When you define objects, fields, and relationships, they become instantly available for you to use in declarative automation features and also in Apex code. Everything defined through the UI can be used programmatically with Apex and Salesforce Object Query Language (SOQL). I'll explain this in more detail in Chapter 4, Apex Basics, under the Working with data in Salesforce section, but, for now, you need to know when objects and/or fields are used/referenced elsewhere in Salesforce.
You won't be able to delete those fields or objects, as Salesforce won't allow that, and it will come up as a big error message...
