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From: mfb@mbunix.mitre.org (Michael F Brenner)
Subject: Re: Looking for Indexed Sequential File Package
Date: 1997/07/17
Message-ID: <5qlskj$3ka@top.mitre.org>#1/1
X-Deja-AN: 257499985
References: <33CCA95E.167EB0E7@avions.aerospatiale.fr>
Organization: The MITRE Corporation, Bedford Mass.
Newsgroups: comp.lang.ada
Date: 1997-07-17T00:00:00+00:00
List-Id: <comp.lang.ada>


Indexed sequential files are not always called that anymore. An indexed
sequential file is a data structure with two components: an indexing
container which keeps a list of keys in sorted order, and a random
access container (falsely called sequential in the title Indexed Sequential).
For the indexing containter, a finite state machine lookup or hash function
may be used, or else you may use a partially balanced or fully balanced
tree, etc. For the random file, you may use an ordinary Ada Stream (unless
you are using the DOS version 3.07), or a large fixed array in virtual
memory, or a direct_IO file. An indexed_sequential_control package would
then simply combine these two containers and provide an interface 
like text_IO, except that the set_position would work, and there would
be insert_key, delete_key, get_position_from_key, get_key_from_position,
get_key_from_record, set_key_in_record, and of course, something like
set_index and get_index would have to work on the file.