Most applications do not explicitly create instances of TDataSetField. Instead, the field components are created automatically, as persistent field components defined in the Fields editor at design time or as dynamic field components created automatically by the dataset. 

Create sets the DataType property to ftDataSet. The AOwner parameter specifies the component, typically a dataset, that becomes the new field's Owner. The Owner is responsible for freeing the component. 

In the rare cases when you must create a persistent field component at runtime, call Create to create and initialize an instance of TDataSetField. After instantiating a TDataSetField, associate it with a specific field by setting its FieldName property to the name of the field. Give the TDataSetField a unique identifier in the Name property. Establish where the field appears in the collection of fields by providing an ordinal number in the Index property. Specify the dataset that contains the dataset field by setting its DataSet property.