Java Interface for LDL++

The Java Interface and its Agent provide the LDL++ Deductive Database System (LDL++) with the remote access capability and a user-friendly graphical user interface. With these two new components, the users can interact with the LDL++ using a Java-enabled web browser from anywhere on the Internet.

The Java Interface and its Agent are integrated with the LDL++ using a three-tier architecture. The Java Programming Language and the HyperText Markup Language (HTML) provides a great combination for creating a presentation application. The Java Programming Language is used to create a user-friendly, menu-driven graphical user interface, with which the users interact to create queries and send commands to the LDL++ server. The query results are translated into HTML, then are presented to the users through an internet browser. The HTML allows the query results to be organized into a table format with is easily comprehensible. The Java Interface provides the following functions:

A User-Friendly, Intuitive, Menu-Driven Graphical User Interface
Eliminates Text-Based Commands
Form-Driven LDL++ Queries
Dispatches HTML Formated Query Results to the Internet Browser
A Simple Text Editor: This allows the users to edit program and data files on-line.

The Agent program mediates between the Java Interface and the LDL++. As illustrated by the little slide-show below:

Click on the applet to move on to the next slide.

The Agent program provides the following services:

Security and User Authentication: Limited access only to authorized users
Communicating to the LDL++ Servers: Due to its security feature, the Java applet can only talk to the server where it originates. The Agent allows the Java Interface to connect to multiple LDL++ servers.
Server Load Balancing: The Agent program keeps track the number of connections from the Java Interfaces to each LDL++ server, and dispatches the new user to the server with the least load.
Translating Query Results into HTML: The Agent program intercepts the query results and translate them into tables using HTML.
HTML and User Files Management: The Agent program stores the intermediate HTML files and manages the user created program and data files.