In the integration engine, building Maps with DML is not so much a hard science as it is a creative art form. Your goal with DML is to write the smallest and most understandable expressions possible to process your data. This can be difficult when dealing with a huge amount of data. DML mapping tasks can often be repetitive, with the same complex patterns recurring in many expressions.

In the early ages of computer sciences, there was no choice but to retype such patterns. Next, most architectures provided explicit call instructions that made tasks easier. In such software architecture, one program might rely on another one to provide a specific service. The service provider is called a subroutine or a function. Subroutines and functions are independent blocks of code that are created only one time and then reused as many times as needed.

Not only do subroutines eliminate repetitive coding, they can also organize massive programs into smaller more structured units that are more understandable and easier to maintain.

You’ve already seen functions earlier in this guide. For example, trimming and padding strings is accomplished using specific functions. These were part of the DML built-in functions. In addition to calling this basic set of functions, you can extend the services that you might use in your DML Block expressions by defining your own specific functions which are called Custom Functions in the integration engine terminology.

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