FieldDefList points to an internal list of field definitions for the dataset. FieldDefList represents a flattened view of the data, meaning that object fields in the dataset may be represented by several simple field definitions that represent the constituents of the object field. To determine the definitions in a hierarchical view, use FieldDefs instead. 

To access fields and field values in a dataset, use the Fields, AggFields, and FieldValues properties, and the FieldByName method. 

FieldDefs 

ObjectView 

TObjectField 

Fields 

AggFields 

FieldValues 

FieldByName