Handbook of Local Area Networks, 1998 Edition:LAN-based Application Development Issues and Solutions
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Performance/Scalability
As monolithic systems became poor performers, the cost of increasing their performance was often astronomicala new mainframe could cost tens of millions of dollars. Carefully segmented client/server architectures can reap the benefits of incremental expenditures on new hardware or devices and also may be able to accommodate incremental software expenditures. Capacity planning for client/server systems is generally easier for monolithic systems because the organization is dealing with smaller pieces of the overall application.
The scalability of client/server systems through application segmentation may offer the biggest advantage to many organizations. It certainly is not the initial start-up costsclient/server systems often cost more to build and maintain. However, a well-defined client/server architecture that considers future scalability will mean that the architecture and applications can expand incrementally rather than having to go through major redesigns and rewrites of all the applications. The availability of many low-cost third-party applications that can easily integrate into enterprise-wide systems eliminates the need to develop everything from scratch. For example, the cadre of software available for the MS Windows platform allows ease of integration with other applications and is growing every day.
Data Access and Management
Client/server systems pose their own set of management concerns that must not be overlooked: There are now more users with greater access to the data. This creates data management and availability problems, as well as systems and data security problems.
Some of these problems can be overcome by the middleware choices that are made. Open System Foundations DCE, for example, implements Kerberos security within its security services to help manage data, applications, and systems security. Some data base vendors now provide DCE integration within their products.
The amount of data and the nature of the data available through the client/server introduce the concept of data as an asset. The flatter organizational structures that are being deployed in many organizations today require their managers to know what is happening within the organizations in real time. As an example, a manager goes over budget because the system is always seven weeks behind on current financial datathe manager has no way of knowing he is going over budget until it is too late. The implementation of a client/server system can provide senior managers with the necessary information in real time.
Protocols and Messaging
Monolithic systems did not need messaging protocols because the whole application was usually within one giant program or there were several large programs that operated in a sequential batch mode and used shared data bases or files. Not only do client/server architectures use messaging protocols, but it is their very existence that makes client/server computing possible. Regardless of whether some of the new middleware products are used in an architecture or if it relies on traditional RPCs or SQL-based interfaces to segment the applications, messaging protocols are being used.
The heavy messaging component to client/server means that these systems rely on communications protocols in a way that monolithic systems developers could never have imagined. These communications protocols are generally transparent to both user and developer. However, they should not be transparent to technology architects. The choices made by these people when they are developing an enterprisewide architecture can have a major impact on the future scalability.
People
The designers and developers for the monolithic systems were a select group who usually stayed with their organizations for many years and were capable of supporting the unique applications they had developed. In todays climate of high employee turnover, faster turnaround times on new capabilities, and return on investment expected in months instead of years, client/server architecture is frequently the only choice. The use of commercial tools and products means there are more specialists available who can come into an organizations IS unit and produce right away. It also provides the ability to outsource systems development and systems operations more easily, thus allowing the IS staff to concentrate on core business competencies.
Business Processes
In an age when businesses must reinvent themselves every few years, business process reengineering is crucial. A well-planned client/server architecture will enable an organizations senior management to make fundamental changes in how the organization conducts business and structures itself while still preserving the investment in core systems technologies.
SUMMARY
Although it is clear that the client/server architecture offers many advantages over previous architectures, it is not to be undertaken without first understanding it. This chapter should help with that understanding and knowledge. Chapter 7-2, which follows, examines the OSFs Distributed Computing Environment and the OMGs Object Management Architectureboth of which are current enabling technologies of client/server computing.
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