JADE (programming language)

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The JADE logo
The JADE logo

JADE is an object-oriented programming language that exhibits a seamlessly integrated object-oriented database management system. It is designed to be an end-to-end development environment, which allows systems to be coded in one language from the database server right down to the clients.

As a programming language, its main competitors are Java and C#, while as a database it competes with other object-oriented database and post-relational databases such as Caché and Matisse as well as traditional relational database software packages such as Oracle and Microsoft SQL Server.

As a proprietary language its usage requires per-process fees to be paid. A free limited licence is available for development.

Contents

[edit] Language

In terms of syntax, JADE is very similar to Pascal; its syntax is based on the language Modula-2, which itself was derived from Pascal. As a newer language, JADE includes innovations not present in either Pascal or Modula-2, however it lacks certain features of other modern object-oriented languages such as C# and Java.

[edit] Programming model

Like all of the other popular programming languages used to create database-driven software, JADE is object-oriented to the core. JADE was designed to have all the most important features of object-oriented programming, but it was also designed to make programming simple, and so does not exhibit the full range of tools that some other languages do. For example, JADE does not support the overloading of methods or operators. This may seem like a big loss to some programmers, but for programming database applications which is what JADE is designed for, the parts that are left out do not end up being major drawbacks, as they are almost never needed. One notable feature that JADE lacks is parameterised constructors and this leads to some dangerous consequences in that one can never know if an object has been properly initialized.

Classes in JADE are kept together in schemas. Schemas serve the same purpose as Java packages or namespaces in .NET, but they are much different in the fact that schemas have a hierarchy, and inherit classes from superschemas. This becomes useful especially when programming using the Model-view-controller methodology, as model classes can be put in one schema, then the controller and view classes can be built on top of the model classes in a subschema.

[edit] Program structure

JADE applications are structured quite differently from most programming languages in the fact that JADE programs are not developed by writing code into long files and then compiling all the files together in one go. JADE programs are actually developed using a user interface that allows programmers to visually create classes and define their properties and methods. Instead of locating methods in large files, programmers select the method they would like to edit and only the code for that particular method is displayed. Also instead of compiling all the code of a program at once, in JADE, each method is compiled individually as soon as the method is completed, meaning code can be checked immediately.

All the code for a JADE application is stored in its object-oriented database. This has a number of advantages. First, it allows for multi-user development, as the database maintains concurrency control. Second, with each piece of the code being a separate object in the database, in a lot of the cases it is possible to recode the system while it is live and online as long as the parts of the system being changed are not in use.

[edit] Features

The main goal of JADE was to give programmers what they wanted — a seamlessly integrated programming language that would allow developers to just create one application that would go from end-to-end instead of having to write three separate applications for the database server, application server and presentation client and then write the code for them to communicate with each other.

[edit] Object-oriented Database

The most striking difference between JADE and other object-oriented programming languages is that its object-oriented database is a native part of its language. For example, when creating an object in JADE, it can be created as transient or persistent. Creating an object as transient is just the same as creating objects in other object-oriented programming languages. The object is simply created in memory, and then lost when the program ends. On the other hand, when an object is created as persistent, when the program ends, the object will still exist and be there the next time the program starts up. In other words, when an object is persistent JADE automatically works in the background to store and retrieve the object in the database when necessary.

There are very few differences between manipulating transient and persistent objects. It has been said that JADE makes it appear to the programmer as if all the objects in the entire database were in local memory. Most of the time, JADE's object-oriented database is used in a multi-user system, and so this statement could be extended to say that JADE makes it appear to the programmer as if all the objects in the database were stored in some shared memory that all users connected to the system could access, even from different computers.

With all of the program code centralised on the database server as well the data, JADE achieves its goal of an end-to-end system, as JADE presents such a level of abstraction that all the client nodes can be programmed as if they were running on the database server. This is very desirable to most database programmers as they don't have to take a number of different technologies and link them together, they just create one application for everything.

The object-oriented database JADE uses is also inherently object-oriented, and so it eliminates the performance loss in an Object-relational mapping system where objects must constantly be converted from their object-oriented form to their relational form. Also like all other commercial database products, JADE has all of the standard features such as atomic transactions, locking, rollback, crash recovery and the ability to keep a Secondary database server synchronised with the main database for reliability and performance reasons.

[edit] Three-tier model

Often for database-driven software, the three-tier methodology is followed. This involves applications being split into three tiers — data storage, processing and presentation. Multiple computers, called nodes may be involved in each tier, and each has a different name. Database servers handle data storage, application servers handle processing and presentation clients provide the user interface. Traditionally, these three tiers would be created by combining three programs and having them talk to each other to create a single system. Having the different programs separate like this has many advantages, the main point that the system becomes scalable — that is, increasing the power of the system simply involves adding more nodes.

Designing a system like this gives the programmer a decision to consider every time they want to code in a particular function. They need to decide whether the function would run best on the database server, application server or presentation client before they begin coding as it will be difficult to change that decision once the functionality is coded into one of the tiers.

This is different for JADE applications, as they are coded as one application from end-to-end. When creating a JADE application, the programmer can think as if they were creating a program that will be running on the database server — as if all the data storage, processing and presentation were happening on one computer. When the program runs on three tiers, JADE automatically knows to run all the code by default on the application server, and to send database requests up to the database server and user interface information down to the presentation client. However, it is very easy for the programmer to switch the location at which a particular method is run and move it up to the database server or down to the presentation client by changing the method properties. Because of this, the decision on where a particular piece of code should run can be made late in the development cycle, and refactoring code to run on different parts of the system ends up being a lot easier because of the way JADE allows end-to-end development of software.

[edit] Types of Clients

Programmers have the facility to allow three different kinds of clients to connect to a JADE system. These three types of clients are named:

  • JADE Forms
  • HTML Documents
  • Web Services

In the same schema, a JADE developer can create many completely separate applications which may provide different interfaces to access the same database.

[edit] JADE Forms

JADE Forms applications are made up of forms, as the name suggests. Client need to connect through the JADE Smart Thin Client or Standard Client to be able to run applications that use JADE Forms.

The Smart Thin Client works by connecting to an Application Server which generally does all the processing on behalf of the Smart Thin Client, meaning the thin client only needs to be responsible for displaying forms and taking input. This means the computer running the thin client does not have to be a very powerful computer, and it does not require a fast network connection as it is not loading data from the database — JADE thin clients are often run over a dial-up connection. This is the reason they are called thin clients, as there is not a heavy requirement on computational power to run these clients. However, as was stated in the last section, it is possible for the programmer to choose to run particular pieces of code on the thin client if it is to the benefit of performance, hence the word smart in Smart Thin Client.

The Standard Client is just the Smart Thin Client combined with the Application Server on one machine. In this case, the node running the client does all of the processing as well as the presentation. Standard clients have greater demands on computational power than thin clients, as they must load data from the database as well as do their own processing.

The advantages of using JADE Forms include:

  • Out of the three kinds of clients, JADE Forms provide the shortest development time of JADE applications.
  • Allows developers to use the same technology end to end.
  • Smart thin clients can be packaged up so they can be installed and run on client computers in several clicks.

The disadvantages are:

  • Cannot reach a worldwide audience as is possible on the world wide web.

JADE Forms have an interesting twist to them though. It is actually possible to run a JADE Forms application through a web browser by changing its mode to web-enabled. When this happens, JADE automatically generates HTML code to make pages that resemble the forms and controls, without any modifications to the code. This is a very quick way for programmers that are not competent with HTML and other web technologies to deliver a program through the web.

[edit] HTML documents

The world wide web is seen as the fastest way to reach vast numbers of people. JADE supports deployment of JADE applications to the web through its HTML documents feature. These work very similarly to ASP.NET, where developers create templates of HTML pages and leave parts in the template for the program to fill in.

The advantages of using HTML documents are:

  • Allows the application to reach a worldwide audience.

The disadvantages are:

  • When JADE applications use HTML documents, they are no longer using the same technology from end to end. Checking at the front end of the system may be done through JavaScript for example.
  • Offloading some of the processing to front-end clients is no longer as easy or secure.

[edit] Web services

Web services are used to allow different programs to communicate with each other from remote locations in an object-oriented form. Web services cannot be accessed directly by human users. One of the uses of web services with JADE is to allow other technologies such as .NET or Java to use JADE as the backend object-oriented database.

[edit] Other client types

JADE is also capable of interfacing with other programs through DLL calls. This allows other programs to access objects and execute methods, and could be used to provide a different interface to a JADE application.

[edit] Multilingual capabilities

JADE natively supports multilingual programs. It does this in several ways:

  • Strings can be marked as translatable, which means they will be change depending on the current language.
  • Many versions of the same form can be created to suit each language. This means interfaces can look entirely different from one language to the next.
  • The developer has methods available to access the current locale of the system and so they can implement their own language-dependent features.

JADE will automatically switch to the language it detects on the system if the language is provided by the developer.

[edit] Portability

Currently JADE applications can be run end-to-end on Windows and Linux. Similar to Java, JADE strives to allow programmers to develop applications once and be able to allow them to run on both of these platforms with minimal changes.

[edit] Code Examples

In this section are some short examples of JADE code.

[edit] Hello World!

In accordance with tradition, the first program that most people ever write in any language is one that says "Hello World!" This is what the code would look like in JADE:

helloWorld();

begin
   app.msgBox("Hello, World!", "Hello, World!", MsgBox_OK_Only + MsgBox_Information_Icon);
end;

or

helloWorld();

begin
   write "Hello, World!";
end;

[edit] History

JADE was originally conceived by Sir Gil Simpson and is currently maintained by the Jade Software Corporation. The first version of JADE was JADE 3, released September 1996. Since then, JADE has grown in popularity and now powers mission-critical information systems that are relied upon by some of the most important corporations in the world. JADE is used throughout all the public hospitals in Australia's Northern Territory and powers the scheduling software for Britain's largest rail freight operator. Currently, the latest version of JADE is JADE 6.1.

[edit] See also

[edit] External links

[edit] Official websites

[edit] Tutorials and resources

[edit] Media coverage

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