|Developing Client/Server Applications|
This chapter explains the purpose of this book, who should read it, and how it fits into the rest of the Net Express documentation. It also explains the imaginary organization and scenarios that are used for the examples in the rest of the book.
This book is aimed at programmers who are developing complete client/server solutions, and who need a practical understanding of the technologies and issues involved in creating real-world COBOL applications with Net Express.
It concentrates on key concepts and practical examples of some of the main technologies supported by Net Express, illustrating typical challenges in designing, programming and deploying field-strength client/server COBOL applications. Its aim is to provide a choice of possible solutions, enabling you to make informed decisions, and giving you the key technical, implementation and rollout details you need. Realistic examples of the techniques described are provided where appropriate.
This book is designed to be used in conjunction with the other online books, which give more detailed information about using the features available in Net Express, and with the Net Express online help system, which provides comprehensive reference and step-by-step task information. References in the text indicate where we suggest you look at specific topics in the online books or help system.
We want this book to be kept right up-to-date with the latest techniques available in Net Express. If you have any ideas or suggestions that you would like us to explore, or if you find a better way of doing something shown in this book, please let us know and share the benefit with other COBOL programmers. For contact information, look up Contacting Micro Focus in the online help contents.
Many of the solutions outlined in this book use code from applications designed around imaginary scenarios to illustrate their application in a real-world situation. These scenarios, detailed below, are designed to illustrate specific applications as realistically as possible, without making the code too complicated to follow. For example, they incorporate some features that would be essential in a real application (such as data validation), but they are not always implemented in a fully realistic environment (for example, using a transaction processing system in conjunction with a database). We suggest you read the general introduction to get a flavour of the scenario, then refer back to the specific phases of implementation as required later in the book.
Gas Services Incorporated is a utility company that supplies gas to domestic customers. It currently services only the Eastern State area, but is in an advanced state of negotiations with competitor WestGas Corporation with a view to a merger and expansion to service the entire state. Each house in the service area has a gas meter that is read by a Gas Services employee at regular intervals, immediately before the customer's gas invoice for the billing period is produced. If the employee cannot read the meter for any reason, the gas consumption for the period is estimated, and the estimated figure is used to produce the customer's invoice. If the customer doesn't agree with the estimated figure, they can read their own meter and supply a figure which is used to produce a revised invoice.
Gas Services customers can currently supply their own meter reading by using Gas Services' telephone Helpline. There is a requirement, however, for customers to be able to connect to a page on the World Wide Web, and update their meter reading using a Web application. The server-side program will be run on the existing Gas Services Windows NT Web server.
Gas Services require a client/server system to support their Helpline operators in dealing with customer enquiries. Customers can call the Helpline to give their own meter reading, to change their choice of gas tariff, to make enquiries about their invoices, or to make general enquiries. The Helpline operators need a system to provide the necessary customer data from the operational database system, and to accept changes they make to the data. The Helpline supervisor additionally requires the system to generate follow-up letters at the end of each working day to customers who have requested a change in their gas supply tariff.
The system will be deployed on a Windows NT server at the Helpline Center. The Gas Services data is held in an Oracle relational database on a UNIX server. The Helpline application server is linked to the database by a wide area network. The Helpline operators use Windows 95 machines that are connected by a local area network. Each operator must be able to deal with up to four customer enquiries at a time.
The merger with WestGas is complete.
Before the merger, Gas Services and WestGas each operated a telephone Helpline and had independent operating databases. The former WestGas database is held in COBOL files on a mainframe. Since the merger, the Helplines have been combined into a single Helpline Center, but the databases for each area are still separate.
Gas Services offers twelve standard gas tariffs. Due to difficult market conditions, however, the corporation has had to introduce a special tariff that can be tailored to the customer's individual circumstances. A telephone Helpline operator can find out how much gas a customer has used over the last twelve months and, using this to represent a typical year's consumption, explore how the charges vary as the tariff variables are adjusted.
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|Developing Client/Server Applications|