Three-Tier Architecture

MiniSQL, developed by Hughes Technologies, is an exceptionally fast DBMS with very low system requirements. It supports a fairly useful subset of the Structured Query Language (SQL). Using it for commercial purposes requires purchasing a license, although free licenses are provided for academic and charity organizations.

The software is distributed in source code form, all bundled up in a gzipped tar file (currently, the latest distribution file is msql-2.0.11.tar.gz). It may be downloaded from the Hughes Technology web site (see Resources). The MiniSQL manual, with all the necessary installation and usage information, is contained in the files msql-2.0.11/doc/manual.ps.gz and msql- 2.0.11/doc/manual-html/manual.html, once the distribution file is extracted. The reader is encouraged to carefully review and follow the instructions contained there. However, it must be noted that two important details are missing from the MiniSQL manual:

In addition to the database server, MiniSQL comes with some other useful utilities: a server administration program, an interactive SQL monitor, a schema viewer, a data dumper and a table-data exporter and importer. The server administration program is required to create the Hangman database that will contain the mystery words. The following command must be executed as root:

/usr/local/Hughes/bin/msqladmin create hangman

/usr/local/Hughes/bin/msql hangman

create table mystery (word char(40), category char(15))\g
insert into mystery values ('elephant', 'animals')\g
insert into mystery values ('rhinoceros', 'animals')\g
insert into mystery values ('gone with the wind', 'movies')\g

The application's middle tier uses Blackdown's Linux Port Java Development Kit 1.2.2, release candidate 4, and CIE's mSQL-JDBC driver for JDBC 2.0. The Java tutorial is one of many excellent places to learn how to access databases from within a Java program; that's why only the specific issues on accessing MiniSQL will be dealt with here.

Before attempting to access the MiniSQL server from a Java application, the corresponding JDBC driver must be installed. The driver may be freely downloaded from The Center for Imaginary Environments web site (see Resources). The distribution file comes with many things, but the most important part is the JAR file that contains the driver itself (currently, the file is msql-jdbc-2.0b5.jar). The easiest way to install the driver is to copy the JAR file to the /usr/local/jdk1.2.2/jre/lib/ext directory (root privileges are required to copy files to this directory).

In order to load the driver from the Java program, the following statement should be executed:

Class.forName("com.imaginary.sql.msql.MsqlDriver");

The connection to the database server is established when executing this statement (ignore line wrap):

Connection con = DriverManager.getConnection
 ('jdbc:msql://localhost:1114/hangman');

The three-tier architecture is a versatile and modular infrastructure intended to improve usability, flexibility, interoperability and scalability. Linux, Java and MiniSQL result in an interesting combination for learning how to build three-tier architecture systems. Nevertheless, more convenient implementations than the one presented here may be produced using component technology in the middle tier, such as CORBA (Common Object Request Broker Architecture), EJB (Enterprise Java Beans) and DCOM (Distributed Component Object Model). The interested reader should review these topics to get a better understanding of the current three-tier architecture capabilities.

Resources