10.3 Location Independence

< BACK  NEXT > [oR] 10.3 Location Independence When you begin to implement a distributed application on a real network, several conflicting design constraints become apparent: Components that interact more should be closer to each other. Some components can only be run on specific machines or at specific locations. Smaller components increase flexibility of deployment, but they also increase network traffic. Larger components reduce network traffic, but they also reduce flexibility of deployment. With DCOM, these critical design constraints are fairly easy to work around, because the details of deployment are not specified in the source code. DCOM completely hides the location of a component, whether it is in the same process as the client or on a machine halfway around the world. In all cases, the way the client connects to a component and calls the component's method is identical. Not only does DCOM not require changes to the source code, it does not even require that the program be recompiled. A simple reconfiguration changes the way components connect to each other. DCOM's location independence greatly simplifies the task of distributing application components for optimum overall performance. Suppose, for example, that certain components must be placed on a specific machine or at a specific location. If the application has numerous small components, you can reduce network loading by deploying them on the same LAN segment, on the same machine, or even in the same process. If the application is composed of a smaller number of large components, network loading is less of a problem, so you can put the components on the fastest machines available, wherever those machines are. Figure 10.4 shows how the same "validation component" can be deployed on the client machine when network-bandwidth between "client" machine and "middle-tier" machine is sufficient, and on the server machine when the client is accessing the application through a slow network link. Figure 10.4. Location Independence With DCOM's location independence, the application can combine related components in machines that are "close" to each other onto a single machine or even into the same process. Even if a larger number of small components implement the functionality of a bigger logical module, they can still interact efficiently among each other. Components can run on the machine where it makes the most sense for them to run: user interface and validation will be on or close to the client, and database-intensive business rules on the server close to the database. < BACK  NEXT >