Qusay H. Mahmoud

Introduction to CORBA CORBA, which stands for Common Object Request Broker Architecture, is an industry-standard developed by the Object Management Group (OMG), a consortium of more than 500 companies. CORBA is actually a specification for creating and using distributed objects. CORBA objects are different from typical programming language objects in three ways: CORBA objects can run on any platform; they can be located anywhere on the network; and they can be written in any language that has IDL mappings. Figure 1 shows a request being sent by a client to an object implementation. The client is the entity that wishes to perform an operation on the object, and the object implementation is the actual code and data that implements the object. The Object Request Broker (ORB), which is the heart of CORBA, is responsible for all the mechanisms required to: (1) find the obj... (more)

Programming Correctness, Assertions and Exception Handling

Program correctness may be viewed as proof that the computation, given correct input, terminated with correct output. The person who invokes the computation has the responsibility of providing the correct input, which is a precondition. If the computation is successful, we say that the computation has satisfied the postcondition. The Eiffel programming language (www.eiffel.com) for example, encourages programmers to provide a fully formal proof of correctness by writing assertions that may appear in the following roles Precondition - a condition an operation's caller agrees to ... (more)

Mobile Agents and Java

Introduction Most of the available distributed systems today are based on the client/server model, which is implemented through some form of remote procedure calls, or remote objects in the case of the object-based model. The client/server paradigm however, has its own limitations. Most notably, all interactions between client and server must go through the network as shown in Figure 1. Another approach that is forming a new paradigm for distributed computing is mobile agents. This approach is attractive since the reliability of the network connection is not crucial. we will see... (more)

Implementing a Security Policy

"Java is the language of network computing," said Lawrence J. Ellison, Chairman and Chief Executive Officer of Oracle Corporation. Basically, there are two main reasons as to why Java is the language of choice for network computing: 1. The APIs provided by the java.net package are very easy to use. Thus, the task of building client/server systems in Java is seamless. 2. It provides an extensible security model that developers can extend to implement their own custom security policies for their client/server systems. Security issues are a major concern in every client/server system. ... (more)