8.Application Development

Why Application?
Ans:
Applications are complete systems that perform specific tasks. The task is defined by the user. For example, you could develop an application to track the location and status of shipping containers.
The goal of an application is to provide information and help users make decisions. To achieve this goal, the application should be easy to use. Applications serve two primary functions:
1. They established and control the user interface
2. They ensure data integrity.
Additionally, applications can be used to build decision support systems and expert systems and expert systems. Each application needs a different combination of these features. As a designer, you need to be aware of the choices and use them to improve your applications.

Application Structure:-
The overall structure is an important feature of any application. The structure or layout define how the user will deal with the application. Most data base applications will use forms and reports as individual components. The first step in designing the structure of the application is to design each form.
The objective of application structure is to organize all of the forms and reports to produce a complete application. It is common to separate a database application into two or three major sections. Sometimes a middle tire is added that consists of program code top define and enforce business rules.


User interface features
Modern windows based applications have several user interface feature that are designed to standardize the look and feel of applications and to make your applications relatively.
Three features are particularly important: Menus, toolbars, help system.

Menus:-
The menu is simply a list of choices that perform some action when selected by the user. Most menus are hierarchical. The windows interface standard specifies that menus should be displayed at the top of the application.


Toolbar:-
A toolbar generally contains a collection of buttons and menu items. When the user click a toolbar button, a predefined operation. A toolbar can contain traditional buttons, and it can contain texture menus. Most toolbars are dockable, when means that users ca drag them to any place on the application windows.


Helps system:-
The goal of this system is to provide the background information and the specific instructions that a user might need to effectively use the application system. Help files can contains text-based descriptions, figures and hypertext links to related topics. The user should be presented with information that is designed to help with the specific task they are working on at the time.


Transactions:-A transaction is defined as a set of changes that must all be made together. Consider the example; you are working on a system for a bank. A customer goes to the ATM and instructs it to transfer $1,000 from savings to a checking account. This simple transaction required two steps: (1) subtracting the money from the savings account balance and (2) adding the money to the checking account balance.
The code to create this transaction will required two updates to the database. For example, there will be two SQL statements: one UPDATE command to decrease the balance in savings and a second UPDATE command to increase the balance in the checking account. If both IPDATE performed successful then transaction is ‘COMMIT’ otherwise ‘ROLLBACK’.


Forms to help user
You can do several things to make your forms easier to use. The key is to understand the business operations and how the forms will be used. For example, you can control combo boxes with the WHERE clause and the NotInList event. You can reduce user keystrokes by user keystrokes by using mouse clicks and double clicks to automatically enter data and perform advanced lookups. Additionally, you can add decisions support features such as statistical analysis, optimization, and simulation. By adding more logic and control to your code, you can add expert system features that automatically computer or estimate key values.


Custom reports
Report writers are good at formatting data for common reports. Some report writers are powerful enough to handle complex reports. Some times you might encounter reports that are difficult to create with a report writer. Sometimes you want to conditional formatting, where the output changes based on the data. So, we should use a report writer to display the final report. Creating reports with the programming is time-consuming.
The fist step is to create a query that provides the data on the report. Then you can write a program that start at top of the query and examines each row. Your code becomes more complex if you want to keep all elements within a group on one page. Then you have to do termine the size of the group before it is printed.
You code must identify the breaks for each group. You should also keep track of the number of lines so that you can identity the end of the page.