To begin programming in PRO-IV the developer must first log on to the PRO-IV environment with the appropriate security level. The development environment presents an initial menu from which the appropriate options can be selected. The diagram below gives an overview of the various menus and options within the standard PRO-IV development environment.

An application is created by working through a series of logically linked input screens that define the structure of the program.

Normally the definitions of the data files will have been created by the system designers since they need only be entered once. To create a new file definition we would need to select the file definition option (the first option from the "Files and Variables" sub-menu.

File Definition

This allows us to define a logical file record layout by specifying a logical file name and the associated file attributes (fields). The structure and associate attributes of individual fields is defined on a central "global dictionary". The logical files (or views) can then be related to physical files or datasets. Once files have been defined to the system and the programs that access them have been created no re-programming is necessary to change the physical location or even the file type making PRO-IV an ideal tool for migrating between different file systems. Once defined, these logical files can be referenced from any application, any number of times, the definition does not have to be re-input into each program.

Once the files have been defined the programs can be written. In the PRO-IV environment the term "Function" is used to refer to what would be called a program or module in other computer languages. To create a new function we would select option 2 from the main menu. This would present a series of linked screens within which we would specify the parameters which make up the function.

Function Definition

PRO-IV has four types of function which are linked together to form a complete application :

• A Screen Function controls user interaction through forms displayed on the VDU.
• A Menu Function allows selection of other functions from a simple list.
• A Report Function allows for the creation and routing of printed output and the manipulation of data records.
• An Update Function manipulates data contained in the files in a "batch" manner.

The Function definition screen records the name, type and title of the function together with such information as the authors name, date entered and descriptive documentation. The default security level and links to following function are also established at this time.

Format/Report Heading

If a Screen or Report function is being written then the system displays a screen for the input of on screen prompts or report headings.

Data Fields

A screen then requires the programmer to defines which fields are to be displayed or printed and they should be to processed.

Characteristics

This integrates the structure of the program with the file access sequence. It allows for sorting and selection of the data items and the nesting of mult-level reports and screens. PRO-IV provides facilities for defining scroll areas (which can optionally be "expanded" or "contracted" by the user) and windows.

Logic

This allows the developer to define subroutines in a BASIC like code for controlling validation, calculation and selection.

Messages

Each function can refer to a list of error and warning messages.

Once the function has been defined, by entering the appropriate responses against screen prompts, the code must be validated and the linkage-table (or object code) generated. This normally takes a few seconds. The function can then be executed (or modified if an error is detected) and tested. As errors are detected during testing (or as the function is developed) the individual screens (or components) can be directly modified without stepping through the sequence again.

The write, test and modify sequence can continue without the need to develop special support environments and without leaving PRO-IV.