.NET Client-Server Technology

Decentralized Applications

Client-server technology developed as applications were decentralized from PCs and mainframe computers. Desktop computers were connected through a network or LANs (Local Area Networks) and WANs (Wide Area Networks). In this equation, ‘clients’ are the machines or programs that request services from another machine or server on the network. The server is linked to databases or the Web and performs the processing of the request and the delivery of the response.

The client provides the interface with which users communicate and make requests. The server programs and data function much like a remote disk drive. The Web is a natural client-server environment. In multi-tier Web servers, the database servers, application servers, and cache servers are all linked. Clients and servers communicate through scripts embedded in Web pages, insuring the intelligibility of requests and responses. The Internet’s main program, TCP/IP (Transmission Control Protocol/Internet Protocol), is written as a client-server program. In a typical client-server communication on the Web, the web browser sends a request for web pages or processing functions from a web or HTTP server located remotely on the Internet. In another configuration, user/client computers use TCP/IP to request files through FTP (File Transfer Protocol) servers locate on the Internet.

.NET is a suite of programs developed by Microsoft that support web services or the ability for personal computers to use the web. This is an alternative to using installed applications to perform services. Web or application services combine human resources, applications, and data. These services are made available through the organization’s web server to respond to a variety of client requests. These requests include broad services like database management or customer relationship management (CRM). However, it can include much smaller detailed services between clients and the Web, such as providing updated bid information in an on-line auction to providing stock or weather quotes. .NET servers support web services by providing clients with interfaces and seamless applications that make the execution of services more centered on the web browser. However, .NET platforms also contribute to the server-side of the equation by providing foundational services for building servers such as web-based data storage and services like Passport, in which users fill in a form once and it is stored for future identity verification.

Development of .NET

.NET developed as a framework in which to build and develop Windows applications. In a traditional Windows application, APIs (Application Program Interfaces) provide the basic tool for building applications. It offers the building blocks for software applications. For example, APIs allowed programmers to write specific functions into programs such as dialog boxes, buttons, etc. However, each new function required a new API to be called upon. Also, APIs required heavy code writing on the part of programmers. Using visual tools products and languages like Visual C++ or Visual Basic simplified, Windows programming developed more sophisticated GUIs (Graphic User Interfaces).

However, Windows APIs needed to be ‘wrapped’ in ‘wrapper classes’. Wrappers are software or data that contain or wrap around other software so that the contained software can exist in another operating environment to insure compatibility. Wrapping is used to make wrapped software behave like an object. OLE (Object Linking and Embedding) was the original technology that allowed applications to communicate with each other in Windows. This technology was upgraded to COM (Common Object Model), Microsoft’s object-oriented programming model. This model defined object interaction within single applications or between different applications.

COM launched ActiveX controls to compete with Java applets. ActiveX controls contain sets of rules defining how applications share information. Microsoft’s ActiveX technology proved more powerful than Java applets because they have access to the entire Windows operating system.

As client-server technology, distributed object-oriented programming (OOP), and the explosion of web services came together, standards like CORBA (Common Object Request Broker Architecture) were developed that specified protocols for transmitting objects over a network. However, this required tight client-server coupling, which meant that these protocols had to be very specific. The client needed to know how to communicate with the server precisely. This required a large deployment effort because of the need for detailed and exact communication.

.NET is Microsoft’s response to the issues described above. Upgrading existing technologies was not enough to compete with Java-based technologies that produced distributed enterprise applications. COM was upgraded to COM+ and DCOM (Distributed Common Object Model). While this addressed distributed programming, it still didn’t address the gaping holes in web services development and distributed application building. .NET did.

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