About Open Dylan CORBA¶
Object Management Group, Inc. describe their CORBA architecture as follows:
The Common Object Request Broker Architecture (CORBA), is the Object Management Group’s answer to the need for interoperability among the rapidly proliferating number of hardware and software products available today. Simply stated, CORBA allows applications to communicate with one another no matter where they are located or who has designed them. CORBA 1.1 was introduced in 1991 by Object Management Group (OMG) and defined the Interface Definition Language (IDL) and the Application Programming Interfaces (API) that enable client/server object interaction within a specific implementation of an Object Request Broker (ORB). CORBA 2.0, adopted in December of 1994, defines true interoperability by specifying how ORBs from different vendors can interoperate.
The ORB is the middleware that establishes the client-server relationships between objects. Using an ORB, a client can transparently invoke a method on a server object, which can be on the same machine or across a network. The ORB intercepts the call and is responsible for finding an object that can implement the request, pass it the parameters, invoke its method, and return the results. The client does not have to be aware of where the object is located, its programming language, its operating system, or any other system aspects that are not part of an object’s interface. In so doing, the ORB provides interoperability between applications on different machines in heterogeneous distributed environments and seamlessly interconnects multiple object systems.
In fielding typical client/server applications, developers use their own design or a recognized standard to define the protocol to be used between the devices. Protocol definition depends on the implementation language, network transport and a dozen other factors. ORBs simplify this process. With an ORB, the protocol is defined through the application interfaces via a single implementation language-independent specification, the IDL. And ORBs provide flexibility. They let programmers choose the most appropriate operating system, execution environment and even programming language to use for each component of a system under construction. More importantly, they allow the integration of existing components. In an ORB-based solution, developers simply model the legacy component using the same IDL they use for creating new objects, then write “wrapper” code that translates between the standardized bus and the legacy interfaces.
CORBA is a signal step on the road to object-oriented standardization and interoperability. With CORBA, users gain access to information transparently, without them having to know what software or hardware platform it resides on or where it is located on an enterprise’s network. The communications heart of object-oriented systems, CORBA brings true interoperability to today’s computing environment.
(At the time of writing, the text above was available at: http://www.omg.org/corba/whatiscorba.html It has been reproduced with permission.)
About the Open Dylan ORB¶
The Open Dylan ORB is a CORBA-compliant ORB written in Dylan, with a native implementation of the Internet Inter-ORB Protocol (IIOP).
The Open Dylan ORB lets you build and run distributed applications in Dylan, straight out of the box. When combined with the Dylan interface to ODBC, you can build 3-tier client-server applications completely in Dylan.
However, the fundamental purpose of the CORBA architecture is interoperability. The ORB’s IIOP implementation provides immediate interoperation with any other ORB you may be using. For example, given a Java ORB you could write GUI clients in Swing or AWT that communicate to servers written in Dylan. Conversely, given a C++ ORB you can build DUIM (Dylan User Interface Manager) clients that talk to C++ servers.
Apart from proving that Dylan could tackle another complex domain, the advantages of building an ORB in Dylan were:
- ORB-vendor independence
The Open Dylan ORB can be married to any existing ORB infrastructure, or introduced first without affecting later ORB procurement decisions.
- “Batteries included”
No need to purchase a separate ORB to get a full system. The Open Dylan ORB provides “instant CORBA” to get distributed Dylan applications up and running without additional procurement or installation.
- Lower impedance mismatch
There is no need to trampoline from Dylan to IIOP via another language binding or via a non-Dylan IIOP engine API.
The Open Dylan ORB is open source, allowing bug fixes and customizations.
- 100% pure Dylan
Providing users with enhanced debugging and interaction facilities available in a homogeneous implementation model.
- Inter-language compatibility
ORB implementations are designed to be interoperable; Open Dylan’s ORB should interoperate with other ORBs that support IIOP version 1.1.
Features of Open Dylan CORBA¶
The following features are supported in Open Dylan’s CORBA implementation:
CORBA 2.0 with parts of CORBA 2.2 (notably the POA)
Internet Inter-ORB Protocol (IIOP) 1.1 (GIOP 1.1)
Portable Object Adapter (POA)
Dynamic Invocation Interface (DII)
Dynamic Skeleton Interface (DSI)
Dylan Language Binding
Open Dylan includes example applications to help you start writing client/server applications in CORBA.
- Hello World
A client/server implementation of the standard Hello World application.
A three-tier client/server implementation of a banking application.
An implementation of a chat program that allows users to communicate across a network.
We study the Hello World and Bank applications later in this book. The Hello World example is ready to build and run, straight out of the box. Before you can use the Bank example, you might need to install some (free) Microsoft ODBC drivers, depending on what you have installed on your computer already. The documentation for the Bank example provides instructions.