To the end user, the client application of a multi-tiered application looks and behaves no differently than a two-tiered application that uses cached updates. User interaction takes place through standard data-aware controls that display data from a TClientDataSet component. For detailed information about using the properties, events, and methods of client datasets, see Using Client Datasets. 

TClientDataSet fetches data from and applies updates to a provider component, just as in two-tiered applications that use a client dataset with an external provider. For details about providers, see Using Provider Components. For details about client dataset features that facilitate its communication with a provider, see Using a Client Dataset with a Provider. 

The client dataset communicates with the provider through the IAppServer interface. It gets this interface from a connection component. The connection component establishes the connection to the application server. Different connection components are available for using different communications protocols. 

These connection components are summarized in the following table:  

Connection components  

also includes a connection component that does not connect to an application server at all, but instead supplies an IAppServer interface for client datasets to use when communicating with providers in the same application. This component, TLocalConnection, is not required, but makes it easier to scale up to a multi-tiered application later. For more information about using connection components, see Connecting to the Application Server.