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From: blakeley@osage.csc.ti.com (Jose' A. Blakeley)
Newsgroups: comp.databases,comp.object,comp.lang.c++
Subject: Use of queries in a programming language.
Message-ID: <1991Jan25.044634.23727@csc.ti.com>
Date: 25 Jan 91 04:46:34 GMT
Sender: usenet@csc.ti.com (USENET News System)
Organization: TI Computer Science Center, Dallas
Lines: 84


  The purpose of this posting is to probe the programming languages
and database communities about the expected need for an associative
query capability in a programming environment.

As a background note, I am part of a research team at Texas Instruments
responsible for building an object-oriented database management system.
Due to a lack of a formal, universally accepted object data model,
we adopted the type system of an object-oriented programming language 
X, where X=C++,CLOS,... as a basic data model for the system. Our approach 
is similar to other efforts currently underway at several OODB companies.
We denote the basic API of the programming language X augmented with
database amenities like persistence, transaction management (concurrency
control and recovery), and type management (data dictionary) as Persistent[X].

To complement Persistent[X] we have built a prototype of an associative
object query capability denoted OQL[X]. One of the primary design goals of
OQL[X] is to provide a smooth integration of query statements with the normal
programming language statements of X. OQL[X] can be seen as a hybrid of
SQL and statements from X. The structure of an OQL[X] query statement is:

  <result> = SELECT <object>
             FROM   <range variable> IN <collection>
             WHERE  <predicate>;

where <result> is a collection-valued variable in a program; <object> describes
the type of the objects in the response collection; <range variable> is a 
variable declared using syntax of a variable declaration in X which ranges 
over the objects of <collection>; <collection> is a collection-valued program 
variable or function, or object stored in the database; and <predicate>
is a Boolean expression describing the condition to be satisfied by the
objects in the response collection.

The following example illustrates the use of an OQL[C++] statement
within a C++ program. People familiar with embeddings of SQL in programs
may wish to compare this code with the amount of code required to 
formulate a similar query in a relational system using embedded SQL.
Note that the use of set-valued variables eliminates the need for cursors.

class Person{public: char* name(); ...};
class Medical_Record{public: Date date(); char* diagnosis();...};
class Patient: Public Person{public: Set<Medical_Record> medical_records();
                                     Physician *physician();...};
...
main()
{
  Set<Patient> mypatients, result;
  Patient p1, p2;
  ...                                   // code that creates instances of
                                        // of patients not shown
  mypatients.Insert_Member( p1 );       // insert a member to the set
  ...
  Query{
  Date *d = new Date( 12, 11, 90 );
  result = SELECT p
           FROM Patient *p IN Patient_Set
           WHERE p->physician()->name()->last() == ``Smith'' 
             &&  EXISTS ( SELECT r
                 FROM Medical_Record *r IN p->medical_records()
                 WHERE r->date() < d  
                   &&  r->diagnosis() == ``flu'' ) ;
  }
};

I would appreciate any information, feedback, or comments from the
programming languages and database communities about the degree of
interest, desirability, and usability of such an associative 
query capability to complement a programming language X. 

Please send your comments to blakeley@csc.ti.com.

If there is enough interest and responses to this inquiry I promise
to summarize them and post them in this news group.

There is also a technical report that provides a full description of
OQL[C++]. I will be happy to send copies to interested people.

Thank you in advance for your help.

// Jose' A. Blakeley
// Information Technologies Laboratory
// Texas Instruments
// P.O. Box 655474, MS 238
// Dallas, Texas 75265   (214) 995-0362.