Designing Functions › Introduction to Functions › Overview of Functions

Overview of Functions

A function defines a list of processes that will operate on the files and fields in your database. CA 2E provides a variety of standard functions to which you can add your own unique processing. CA 2E uses the information contained in your data model to provide all of the default processing for the standard functions.

The set of standard functions consist of database functions, device functions, and user functions. Note that only the first two will be covered in this tutorial. The standard functions consist of a variety of function types, each of which performs a specific process. For example, the Edit File (EDTFIL) function type retrieves data from a file and lets the end user update that data using an interactive panel. The Print File (PRTFIL) function type prints a report of the data from a file. The Create Object (CRTOBJ) database function creates a record in your database.

A function can be implemented either as a separate program or as a subroutine within a program as follows:

• An external function is implemented as a separate high-level language (HLL) program. Each external function is attached to an access path. In general, the standard device functions are external functions; for example, the Edit File function. The only exception is the Print Object (PRTOBJ) function that is covered in a later chapter of this tutorial.
• An internal function is implemented as source code within that of the calling program; in other words, it is implemented as a subroutine. All the standard database functions are internal functions; for example, the Create Object function.

There need not be a one-to-one correspondence between a function and the program that implements it. You can link functions together to create larger processes that become the building blocks of your applications; namely, several internal functions may be implemented as a single program. In other words, a function is a unit of specification, not implementation.

The standard functions may have the following components. Note that not all function types have all four components.

• Device design—Specifies the layout of the panel or report used by the function
• Action diagram—Specifies the processing steps that make up the function (includes default processing and processing that you define)
• Function options—Specifies default features of a function
• Function parameters—Specifies fields to be passed into the function and returned from the function at run time

Each of these components is discussed in this chapter.

In addition to the standard functions, CA 2E provides message functions, function fields, and built-in functions, which perform low-level processing such as arithmetic operations. These will all be discussed in this and the following chapters.