The method Key Retrieval controls the Key Selection. It determines which Fields are shown in a Key Selection screen and which actual parameters are passed to the Data Retrieval method. Key Retrieval is a variant of Data Retrieval.
Depending on the connection type one or more mechanisms are available for key and data retrieval. Some mechanisms make use of ITP internals, other mechanisms use programs or SQL queries. The result of the Key Retrieval method should always be a data set (record) that obeys the Parameter and Field definitions of the Entry.
The Connection Types are implemented in the ITP DataManager. Every time that Key Retrieval is required in a Model, the Key Retrieval method and parameters are sent to the ITP DataManager. The ITP Data Manager takes care of all communication involved in executing the Key Retrieval method and receiving the results. The ITP environment only communicates to external databases through the DataManager.