Green and Payne's (1984) analysis of
command language structure suggested that Language 3 is particularly difficult to learn because it utilizes two conflicting organizational principles.
Parlane, the natural language database interface system produced by BBN Laboratories (BBN), translates natural language input into structured query language (SQL), the standard
command language used with many database management systems, and the SQL commands are then applied to the underlying database.
According to Shneiderman [25], even expert users are penalized by poor design: "Even expert users of interactive editing or
command languages were found spending one-third of all commands in making or correcting errors." Although it may not always be possible to translate the costs of these errors on a per-error basis, it is obvious that the time required for error correction imposes costs in both staff and computer time.
2a) Useful documentation on using the STN Messenger
command language is: Getting Started on STN, December 1990, STN International; Getting Started in CAS ONLINE, February 1988, Chemical Abstracts Service; Finding and verifying CAS Registry Numbers on STN, January 1991, STN International; STN FaSTNotes, various titles, June 1990, STN International; Searching STN.
Shneiderman [8] described five primary interaction styles available to a software designer: (1) form fill-in, where the user moves from field to field on the screen to enter the necessary or requested data; (2) menu selection, where the user chooses from among a set of options displayed on the screen; (3)
command language, where commands are entered directly into the system; (4) direct manipulation, where the user moves the cursor around the screen with a pointing device in order to manipulate a representation of some action or object; and (5) natural language, which is much like a
command language except that it uses a spoken language such as English.