An Introduction to Functions › Building Block Approach, an Overview

Building Block Approach, an Overview

Building an application is a matter of defining or choosing the right functions and putting them together to meet your requirements. CA 2E functions serve as the components for applications. When implemented, several functions may work together as a single HLL program. Functions can also call other functions, based on default connections or action diagram specifications.

The process of designing your application should include the step of breaking down your operations into simple building blocks. Each CA 2E function performs a unique, defined task. Correlating your operations with these functions is called function normalization. The structure of CA 2E provides the means for normalizing functions and for constructing more complex functions from the simple building blocks.

Function normalization encourages the use of a single function to perform a single defined action. More complex functions can then be constructed by linking together lower level functions. This approach allows for development and testing to be incremental and reduces the overall development and maintenance effort.

For example, to construct a routine to calculate the days between two dates you should first construct a function to convert a date into one absolute day number. You can then use this function to convert the from and to dates to an equivalent numeric value. Then you can use subtraction to yield the difference. This same low level function can also be used in other functions that add, drop, or subtract days from a date, without the need to redevelop or repeat logic.

The CA 2E building block approach gives you categories of functions, and each category has a specific implementation as follows:

• Standard device functions—Specify interactive or report programs. These functions have device designs attached to them. These functions work together with the database functions to view, add, change, or delete data in your files.
• Internal functions—Are implemented as source code within calling functions.
• External functions—Are implemented as HLL programs such as batch processing and device functions.
• Built-in functions—Execute common low-level functions and such tasks as arithmetic operations and commitment control.
• Function fields—Specify how to calculate derived fields. A derived field is any field with a value that is calculated from other fields when accessed in a routine, rather than physically stored in the database.
• User-written functions—Specify user-written processes with either action diagrams or RPG or COBOL subroutines or programs.

For more information:

• About adding functions, see the chapter Defining Functions.
• About action diagrams, see the chapter Modifying Action Diagrams.