Use TADCustomConnection to establish connection to a DBMS and manage associated datasets. 

This class hides some of properties, allowing to control visibility of properties by descendant classes. End users should use TADConnection.

TADCustomConnection = class(TCustomConnection, IUnknown, IADStanOptions, IADStanErrorHandler, IADStanObject, IADPhysConnectionRecoveryHandler, IADPhysTransactionStateHandler);

Working with Connections, Managing Transactions, TADConnection, IADPhysConnection