An ODBC Interface for the
Unicon Programming Language

Federico Balbi and Clinton L. Jeffery

Unicon Technical Report #1b

June 28, 2002


The implementation of an ODBC interface for the Unicon language allows programmers to interface their applications to local and remote database management systems with a high level of interoperability and SQL language support.


Department of Computer Science
The University of Texas at San Antonio
San Antonio, TX 78255

Department of Computer Science
New Mexico State University
Las Cruces, NM 88003







This work sponsored in part by the National Library of Medicine.


1. Introduction

The Unicon ODBC interface consists of a data type and a set of new functions to enable Unicon programs to access database management systems (DBMS). The standard language to retrieve and manipulate data in a DBMS is the structured query language SQL.

1.1 Overview

ODBC is a programming interface (API) to access local and remote database management systems. ODBC is a de facto industry standard and works on many different operating systems and programming languages. It shields programmers from the complexity of different databases and the communications software used to access the data. ODBC defines an object called a "data source" that is referenced by name and maps its name to the exact location of data (network software, server name, database name and user information if needed).

1.2 ODBC Architecture

ODBC allows multiple applications to access to multiple data sources using an architecture (Figure 1) that consists of several layers:

Figure 1: ODBC Architecture

Applications call ODBC functions. The Driver Manager decides which driver is needed and loads it into memory. After this the Driver Manager routes ODBC calls to the driver.

The minimum capability required from a driver is to be able to connect to a server, send SQL statements and retrieve the results. What is important is that the Driver Manager hides all the details related to the server so the application does not need to know if the data is on a local file, a network file server or a remote host.

1.3 Client/Server Model

ODBC was designed to work with the client/server model (Figure 2) in order to satisfy the following requirements:

Figure 2: Client/Server Model

1.4 ODBC Installation

After deciding which DBMS an application is going to use it is necessary to install its related ODBC driver to let the application establish a connection with the DBMS.

For our ODBC tests we decided to use MySQL. MySQL is a free SQL server downloadable at and available for most popular platforms. We tested both Linux and Sun/Solaris version. MySQL comes with MyODBC, the ODBC driver for the server, and it can be downloaded at the same web site. There are driver versions both for Unix and Windows.

MyODBC comes with a standard Windows setup.exe program. At one point during setup you have to physically click on MyODBC within a list-box to install successfully, but otherwise installation is uneventful. If installation is successful, when you are finished you will be able to see your MySQL data source(s) from the ODBC Data Sources control within the Windows Control Panel (Figure 3).

Figure 3: The Control Panel windows

Figure 4: The Driver Manager

This control comprises the main interface of the ODBC Driver Manager (Figure 4). The ODBC Driver Manager lists the ODBC drivers installed for different DBMSes. We can add new drivers, remove or configure existing ones within this control. The MyODBC setup program automatically adds and configures the driver in the Driver Manager's driver list.

After installing MyODBC we can open the Driver Manager and take a look at the different configuration parameters (Figure 5).

Figure 5: MyODBC configuration

The MyODBC configuration panel has the following fields:

All the other check-boxes are driver options. Of particular note are the following options:

1.5 Unicon ODBC Interface

The Unicon ODBC interface is a set of built-in functions that allow an easy way to write SQL database applications.

The function set can be divided in four main groups. A synopsis of these functions is given here. The reference section towards the end of this document describes them in detail.


2. An Example Phonebook Application

A typical database application performs the following tasks:

This section presents a simple Unicon phonebook application that takes advantage of the ODBC interface and work with MySQL server. The example will show how to use the main Unicon ODBC functions in order to connect, read and write data on a DBMS.

Our application will have the following menu:

Note that this application assumes a preexisting database server. a user account on that server, and a table on the server has been created to store the phone book information. Letís create a phones table on our server with the following columns:

Column Name


Name (KEY)






We could create such a table within the application by appropriate Unicon ODBC calls, but perhaps it is more typical for such database administration tasks to be performed separately by a database administrator. From our server machine we invoke the mysql client program to talk to the SQL server:

[fbalbi@icon bin]$ ./mysql -ufbalbi -p mysql
Enter password:
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 96 to server version: 3.22.15-gamma

Type 'help' for help.

Now let's create the example table with the column Name as primary key:

mysql> create table phones (name varchar(40) primary key, phone varchar(12), address varchar(60));

Query OK, 0 rows affected (0.04 sec)

mysql> describe phones;

| Field   | Type        | Null | Key | Default | Extra |
| name    | varchar(40) |      | PRI |         |       |
| phone   | varchar(12) | YES  |     | NULL    |       |
| address | varchar(60) | YES  |     | NULL    |       |
3 rows in set (0.01 sec)

Now the table is properly created and empty, in fact the following select commands returns an empty set:

mysql> select * from phones;

Empty set (0.00 sec)

Here the full list of our phonebook application. As an exercise, you may wish to consider how you would extend this application to include the above table-creation task as another menu option. Hint: the function sql() may come in handy.

# global variables

global db
global user, password

record person(name, phone, address) # database row

procedure main() # main program
  write("*** Unicon ODBC phonebook ***\n\n")
  login() # get user name and password
  # connect to mysql data source and open table "phones"
  db := open("mysql", "o", user, password)

  if &errornumber~=0 then { # error during login
  else {
    getdbinfo() # print database information
    repeat {
      menu() # print menu options 
      option := read()

      case option of {
        "i": insertphone()
        "d": deletephone()
        "u": updatephone()
        "l": listphones()
        "q": break
        default: write("*** wrong selection ***")
    close(db) # close table and database connection

# user information
procedure login()
  writes("user: ")
  user := read()
  writes("password: ")
  password := read()

# get database name and version
procedure getdbinfo()
  info := dbproduct(db)
  write("\nDBMS: ", info["name"])
  write("version: ", info["ver"])

# display menu options
procedure menu()

# insert a new record
procedure insertphone()
  writes("name: ")
  name := read()
  writes("phone: ")
  ph := read()
  writes("address: ")
  addr := read()
  sql(db, "INSERT INTO phones VALUES(" ||
           name || "," || ph || "," || addr || ")")
  if &errornumber~= 0 then
    write("*** couldn't insert person ***")

# remove a record 
procedure deletephone()
   writes("name to remove: ")
   name := read()

   # delete row with specified name column
   sql(db, "DELETE FROM phones WHERE name='"||name||"'")

# update a record
procedure updatephone()
  writes("name to update: ")
  name := read()

  # select all columns of rows with specified name column
  sql(db, "SELECT * FROM phones WHERE name='"||name||"'")

  if row := fetch(db) then { # data found
    writes("phone (",row["phone"],"): ")
    writes("address (",row["address"],"): ")

    # update row on server
    sql(db, "UPDATE phones SET " ||
                   "phone='" || row["phone"] || "'" ||
                   ",address='" || row["address"] || "'" ||
                   " WHERE name='" || row["name"] || "'")
  else write("\n\n*** person not found ***")

# list all people in the database
procedure listphones()
   sql(db, "SELECT * FROM phones") # select all columns and all rows

   while row := fetch(db) do { # while data found
      # write row fields
      every i:=(1 to *row) do writes("[",row[i],"]")

3. Unicon ODBC Function Reference

With the exception of open() which returns a file reference to an ODBC connection, all these functions generally take an initial parameter (designated by f which must be an ODBC file previously opened with open(...,"o"). Since it is used consistently everywhere, this initial parameter is not given in the detailed description of the rest of the function parameters.

: closes an ODBC file

Code Example

procedure main()
  # ...program body...

  close(db) # close table and disconnect

dbcolumns(f,t) : L
: return column information related to table t in database f


Return Type: list of records with the following string fields:

Code Example

procedure main()
   f := open("mysql","o","federico","") # open table
   colinfo := dbcolumns(f) # get columns information
   write("column info\n")

   every i := 1 to *colinfo do { # for each column
      writes("col #",i,": ")
      every j := 1 to *colinfo[i] do # write column's info
   close(f) # close table and connection to the database

: returns information about the driver being used

Return Type: Record with the following string fields:

Code Example

procedure main()
   f := open("mydb","o","fbalbi","") # open mytable

   dinfo := dbdriver(f) # get driver information record

   write("driver name     : ", dinfo["name"])
   write("driver version  : ", dinfo["ver"])
   write("driver ODBC ver : ", dinfo["odbcver"])
   write("connections     : ", dinfo["connections"])
   write("statements      : ", dinfo["statements"])
   write("data source name: ", dinfo["dsn"])

   close(db)	 # close database connection

: returns information about the primary key columns

Return Type: list of records with the following string fields:

Code Example

procedure main()
   f := open("mydb","o","fbalbi","passwd") # open table

   write(*f, " row(s) selected")
   write("\ntable keys")

   krec := dbkeys(f) # retrieve primary key information

   every i := 1 to *krec do {
      r := krec[i]
      write("[", r["col"], "]") # print key name
   close(f) # close table

: returns information about the limits applied for identifiers and clauses in SQL statements.

Return Type: record with the following string fields:

Code Example

procedure main()
   f := open("mydb","o","fbalbi","") # open mytable

   dbl:=dblimits(f) # get DBMS limits information

   # print out all DBMS limits
   every i := 1 to *dbl do write(dbl[i])

   close(f) # close table

: returns information about the DBMS accessed by the driver

Return Type: record with the following string fields:

Code Example

procedure main()
   f := open("mydb","o","fbalbi","mypasswd") # open table

   p := dbproduct(f) # get DBMS product information

   write("product name: ", p["name"]) # print product name
   write("product ver : ", p["ver"])  # print product version

   close(f) # close table

dbtables(f): L
: get information about tables stored in database f

Return Type: list of records with the following string fields:

Code Example

procedure main()
   f := open("mysql","o","fbalbi","xxxxxxxx")
   # get current database tables information 
   tablelist := dbtables(f)

   # write number of tables
   write("size list = ", *tablelist) 

   every i := 1 to *tablelist do { # for each table

      # print table information fields
      every j := 1 to *r do writes("[",r[j],"]") 

  close(f) # close table

: fetches and returns a row from a rowset

Return Type: record with fields names equal to the selected table columns (use sql(db, "SELECT...") for column selection)

Code Example

procedure main()
   f := open("mydb","o","fbalbi","mypass")

   # select 3 existing columns from table mytable
   sql(f, "SELECT id, name, amt FROM mytable")

   # *f = number of selected rows
   # may not work with some DBMS
   write(*f, " row(s) selected")

   write("\nrow values")

   # fetch returns a record whose
   # fieldnames are the column names selected with a SQL SELECT
   # in this example we can reference fields using row["id"],
   # row["name"] and row["amt"]

   while row := fetch(f) do { # while rows to retrieve
      every col := 1 to *row do  # for each col of row
         writes("[",row[col],"]") # write row field

   close(f) # close table

open(db, "o", username, password)
: connect to a database and returns the associated ODBC file.


Code Example

procedure main()
   # open "mytable" in mydb data source name defined in
   # ODBC Data Sources (see Windows 9x Control Panel folder)
   # using username "federico" and password "mypassword"

   db := open("mydb","o","federico","password")
   # ...program body...

  close(db) # close table and disconnect

sql(f, query)
: submits an SQL query using the connection opened by f


Code Example

procedure main()
   # connect to DBMS and open table

   # prepare SQL query string to create an employees table
   # of 5 columns

   query := "CREATE TABLE employees (id INTEGER PRIMARY KEY,_
             name VARCHAR(40), phone VARCHAR(12), DOB DATE,_
             pay FLOAT)"

   sql(db, query) # execute query
   close(db) # close

4. Conclusions

This interface is a successful, albeit low-level interface to SQL databases. It has been tested and proven effective on large real world data sets. SQL commands are constructed as strings, and Unicon excels at such text manipulation. This interface does not provide Unicon programmers with higher level abstractions of database capabilities. For example one original design goal was to allow programmers to interact with a database with minimum knowledge of SQL. For example, the built-in table data type does not match the SQL table abstraction exactly, but with proper operator support interactions with SQL tables could look very similar to interactions with Unicon tables.

Appendix: Unicon ODBC Implementation Notes

The implementation of the ODBC interface includes changes to several files of the Unicon runtime system, as well as the addition of a new file for the new functions that were added.

New files

Modified files

ISQLFile type

In Unicon an ODBC connection to a database is similar to a file operation. Internally this is represented by the following C structure:

#ifdef ISQL             /* ODBC support      */
  struct ISQLFile {     /* SQL file          */
    SQLHDBC hdbc;       /* connection handle */
    SQLHSTMT hstmt;     /* statement handle  */

The field hdbc is used to keep the connection information associated to a particular ISQLFile file. hstmt is the statement structure that saves the results or dataset returned by an ODBC operation. The design of the interface is table oriented, which means that for each table we open a new connection.

In the future we will consider the possibility to associate a file to a database. This would let us open a connection for each database and share the same connection for each table within the same database. In this way we can open a file and use more than a table.

Actually when open(DSN,"o",user,password) is called Unicon allocates an ISQLFile object and initializes the structure fields in the following way:



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