On top of the services framework sit two application models: the Windows (Win Forms) application model and the Web application model. The Win Forms application model is quite similar to existing Windows-based forms packages. It allows developers to take advantage of the rich user interface features of Windows. Win Forms also takes advantage of the Microsoft .NET Framework runtime to reduce the total cost of ownership for Windows-based client applications. Since most of the common services are provided by the runtime, the client application has to only provide application-specific logic. Moreover. Client applications developed using Win Forms can avail of the built-in security model of the runtime.
Application deployment and versioning is quite simple, as has already been seen. Applications do not have to contend with version conflicts while using components.
Web Application Model
The Web application model also sits on top of the services framework. It basically comprises of Web services and Web applications.
1. Web Services
A Web Service is simply an application that is delivered as a service using Internet standards. It has its own URL and can be requested directly by the client. The application is executed and the
requested information is returned to the client. A Web service can be integrated with other Web
services to provide composite functionality to clients. It thus integrates component-based technologies and the Web to provide services to clients. The client only needs to know which Web service to access and the URL of that Web service t6 access it. The client is not concerned with the actual implementation of the Web service. A Web Service thus represents black-box functionality. The black-box provides well-defined interfaces, called contracts that describe the services provided. These services can be used either locally or remotely along with application-specific code to develop custom Web applications. For example, an online store can use Login services, authentication services, personalization focalization services, cataloging services, payment processing services and shipment services to do its business. It may package all these services together to give a distinct look and feel to its site.
The black-box functionality of Web services is akin to that of component technologies. But. Component technologies use specific protocols such as DCOM. RMI. or IIOP These protocols require, specific and homogeneous infrastructures on both the client and service machines. But, on the Intermit. it is very difficult to control or even know the client-side environment. Hence, Web services cannot use the protocols used by component technologies to communicate with clients. Instead, they use Web protocols and data formats such as HTTP and XML.
