typedef struct a_text_source {
   a_sql_uint32 ( SQL_CALLBACK *begin_document )( a_text_source *This );
   a_sql_uint32 ( SQL_CALLBACK *get_next_piece )(
                                a_text_source *This
                                , unsigned char ** buffer
                                , a_sql_uint32* len );
   a_sql_uint32 ( SQL_CALLBACK *end_document )( a_text_source *This);
   a_sql_uint64 ( SQL_CALLBACK *get_document_size )( a_text_source *This );
   a_sql_uint32 ( SQL_CALLBACK *fini_all )( a_text_source *This );
   a_server_context     *_context;

   // Only one of the following two members can have a valid pointer in a given implementation. 
   // These members point to the current module's producer
   a_text_source        *_my_text_producer;
   a_word_source        *_my_word_source;

   // Following members have been reserved for
   // future use ONLY
   a_text_source        *_my_text_consumer;
   a_word_source        *_my_word_consumer;
} a_text_source;