Mainframe-Centric Client/Server Computing

Mainframe-Centric Client/Server Computing
The mainframe-centric model uses the presentation capabilities of the workstation to front-end existing applications. The character mode interface is remapped by products such as Easel and Mozart. The same data is displayed or entered through the use of pull-down lists, scrollable fields, check boxes, and buttons; the user interface is easy to use, and information is presented more clearly. In this mainframe-centric model, mainframe applications continue to run unmodified, because the existing terminal data stream is processed by the workstation-based communications API.
The availability of products such as UniKix and IBM's CICS OS/2 and 6000 can enable the entire mainframe processing application to be moved unmodified to the workstation. This protects the investment in existing applications while improving performance and reducing costs.
Character mode applications, usually driven from a block mode screen, attempt to display as much data as possible in order to reduce the number of transmissions required to complete a function. Dumb terminals impose limitations on the user interface including fixed length fields, fixed length lists, crowded screens, single or limited character fonts, limited or no graphics icons, and limited windowing for multiple application display. In addition, the fixed layout of the screen makes it difficult to support the display of conditionally derived information.
In contrast, the workstation GUI provides facilities to build the screen dynamically. This enables screens to be built with a variable format based conditionally on the data values of specific fields. Variable length fields can be scrollable, and lists of fields can have a scrollable number of rows. This enables a much larger virtual screen to be used with no additional data communicated between the client workstation and server.
Windowing can be used to pull up additional information such as help text, valid value lists, and error messages without losing the original screen contents.
The more robust GUI facilities of the workstation enable the user to navigate easily around the screen.
Additional information can be encapsulated by varying the display's colors, fonts, graphics icons, scrollable lists, pull-down lists, and option boxes. Option lists can be provided to enable users to quickly select input values. Help can be provided, based on the context and the cursor location, using the same pull-down list facilities.
Although it is a limited use of client/server computing capability, a GUI front end to an existing application is frequently the first client/server-like application implemented by organizations familiar with the host mainframe and dumb-terminal approach. The GUI preserves the existing investment while providing the benefits of ease of use associated with a GUI. It is possible to provide dramatic and functionally rich changes to the user interface without host application change.
The next logical step is the provision of some edit and processing logic executing at the desktop workstation. This additional logic can be added without requiring changes in the host application and may reduce the host transaction rate by sending up only valid transactions. With minimal changes to the host application, network traffic can be reduced and performance can be improved by using the workstation's processing power to encode the datastream into a compressed form.
A more interactive user interface can be provided with built-in, context-sensitive help, and extensive prompting and user interfaces that are sensitive to the users' level of expertise. These options can be added through the use of workstation processing power. These capabilities enable users to operate an existing system with less intensive training and may even provide the opportunity for public access to the applications.
----Patrick Smith