| A typical example of when you might consider a client/server solution would be the
following: Imagine that you are responsible for a departmental-level application that
accesses data residing on a LAN or file server. Various people within your department may
use this application. As this data becomes of greater use to your department, other
applications are created to make use of this data. Suppose this data becomes of interest
to other departments within your company. Now, additional applications will have to be
built for these departments. This may also require you to move the data to a database
server to make it more globally available. The Client
The client can be either a GUI or non-GUI application. Delphi allows you to develop both
the client and any middle layer application servers in three-tier models. The database
server is most likely developed using an RDBMS such as Oracle. Client applications provide
the interface for users needing to manipulate data on the server end. Through the client,
services are requested of the server. A typical service might be, for example, adding a
customer, adding an order, or printing a report. Here the client simply makes the request
and provides any necessary data. The server carries the responsibility of processing the
request. This doesn't mean that the client is not capable of performing any of the logic.
It's entirely possible that the client can carry out most, if not all, of the business
logic in the entire application. In this case, this is what we refer to as a fat client.
The Server
The server provides the services to the client. It waits for the client to make a request
and then processes that request. A server must be capable of processing multiple requests
from multiple clients and also must be capable of prioritizing these requests. More than
likely, the server will run continuously to allow constant access to its services.
The Three-Tiered Model
Here, the client is the user interface to the data. The remote database server is where
the data resides. The client application makes requests to access or modify the data
through an application server or Remote Data Broker. It is typically the Remote Data
Broker where the business rules exist. By distributing the client, server, and business
rules on separate machines, designers can more effectively optimize data access and
maintain data integrity for other applications in the entire system. Delphi adds powerful
capabilities for developing three-tier architectures with the MIDAS technology.
For more information send request to: info@softcorporation.com
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