This topic uses examples to illustrate the interaction between the (the Provider) and a CDSC when VDATA and HDATA are implemented. The examples are based on the example survey described in Handling hierarchical data, earlier in this section.

When the Provider retrieves the records for the Area, Age, and Transport columns from the example survey's VDATA table, the Provider first creates a new Command object by calling the Source object's CreateCommand property. The Provider indicates to the CDSC which columns to retrieve by creating three DataBinding objects (one for each of the Area, Age, and Transport columns) and adding them to the Command object. When the Provider calls the Command object's MoveFirst subroutine, the CDSC stores the values North, 30, and Car in the three DataBinding object's Value objects, ready for the Provider to retrieve. When the Provider calls MoveNext, the CDSC stores the values North, 30, and Bike in the Value objects.

The Provider calls MoveNext a further six times to update the value of the three DataBinding objects. The CDSC tells the Provider when to stop by setting the EOF property on its Command object to true. The Provider therefore obtains the following information:

To illustrate how the Provider adds new data records, consider an extra person being included in the example survey. The inclusion of the new person in the VDATA table requires an additional row to be added to the table. Suppose an additional person moves into the flat in the North. The details for this person are:

The sequence when a new record is added is as follows:

To cancel the addition of the new record, the Provider would call Delete instead of Update, and no data should be written by the CDSC.

When writing data, the CDSC should store NULL (or the best default it can use) for any variables that weren't bound.

The data would then resemble the following table: