For the program action that reads a record, the caller supplies a book's stock reference number, title, or author in the appropriate field in the lnk-b-details group. The program looks it up in the indexed file and returns the data back to the lnk-b-details group. Therefore, the program uses the fields contained in the lnk-b-details group as both input and output. On input, the program expects the stock number, title, or author to be supplied; the other data items in lnk-b-details are ignored. On output, lnk-b-details is used to return the record indicated by the supplied stock number, title, or author.