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From: marti@ethz.UUCP (Robert Marti)
Newsgroups: comp.databases
Subject: Call Interfaces to RDBMSs
Message-ID: <168@bernina.UUCP>
Date: Tue, 4-Aug-87 06:33:18 EDT
Article-I.D.: bernina.168
Posted: Tue Aug  4 06:33:18 1987
Date-Received: Sat, 8-Aug-87 08:56:51 EDT
Organization: ETH Zuerich, Switzerland
Lines: 50

The prevalent approach to offer set-oriented access to a relational
database from an application written in a langauge such as C seems
to be pre-compilation.   For example, embedded SQL uses database
statements bracketed by EXEC SQL and END-EXEC keywords while embedded
QUEL uses the ## marker on the beginning of each line.  The pre-
processor strips these statements and replaces them by procedure
calls to the DBMS.

There are two drawbacks to such a solution:  The first and minor one
is that such constructs look unpleasant in the source.  The second
and major drawback is that a pre-processor has to written for each
new host language for which database access has to be supported.
This may be OK for vendors who can easily tailor their existing
pre-processor to a new language, but for customers without access
to source this is a major pain (you know where :-)

Since we would like to use Modula-2 to access relational databases
-- Modula-2 is the language our programmers (students) know best --
we'd much rather have an interface in the form of a library of
procedures.  An example of such an interface is provided by Sun's
enhanced version of UNIFY which supports query_open, query_next
and query_close statements as shown below:

  char[30] emp_name;
  int emp_sal;

  cursor = query_open("select name, salary from emp");
  while (query_next(cursor, "%s %d", emp_name, &emp_sal) == DB_SUCCESS) {
    /* process the retrieved stuff */
  }
  query_close(cursor);
               
(Note that the "%s %d" string in query_next is a format string as used
in the well-known scanf, printf etc. functions.)

Unfortunately, UNIFY is weak in other areas, namely in its support for
transactions and views.  Therefore my questions:  Are there any other
UNIX DBMS products out there which support relational queries via a
call interface as opposed to a pre-processor?  Do INGRES or Oracle
explain in their manuals how to interface to their database system
without using the pre-processor?

Thanks in advance for any explanations on the subject.

Bob
-- 
Robert Marti                    Phone:       +41 1 256 52 36
Institut fur Informatik
ETH Zentrum/SOT                 CSNET/ARPA:  marti%ifi.ethz.ch@relay.cs.net
CH-8092 Zurich, Switzerland     UUCP:        ...seismo!mcvax!ethz!marti