An entry describes the input parameters and the output parameters for the Data Retrieval. Data Retrieval is the core of the ITP Data-Text merge process. The formal parameters of an Entry describe the input parameters of the Data Retrieval method. The Fields of an Entry describe the output parameters of the Data Retrieval method. Which method should be called is defined in the Entry. ITP has no knowledge what the Data Retrieval method does or how it performs its operations. ITP will accept any Data Retrieval method that obeys the calling convention, parameter definitions and field definitions.
Once the actual parameters for an Entry are known the Data Retrieval method is started, obeying the calling conventions of the Connection Type. The actual parameters of the entry are passed to the Data Retrieval method. The actual parameters can be provided through several different mechanisms:
Depending on the connection type one or more mechanisms are available for data retrieval. Some mechanisms make use of ITP internals, other mechanisms use programs or SQL queries. The result of the data retrieval method should always be a data set (record) that obeys the Field definitions of the Entry.
The Connection Types are implemented in the ITP DataManager. Every time that Data Retrieval is required in a Model, the Data Retrieval method and parameters are sent to the ITP DataManager. The ITP Data Manager takes care of all communication involved in executing the Data Retrieval method and receiving the results. The ITP environment only communicates to external databases through the DataManager.