The connection between a control and a database is handled by a class called a data link. The data link class that connects a control with a single field in a database is TFieldDataLink. There are also data links for entire tables. 

A data-aware control owns its data link class. That is, the control has the responsibility for constructing and destroying the data link. For details on management of owned classes, see Creating a graphic control

1. Declaring the class field.
2. Declaring the access properties.
3. Initializing the data link.