A Function rule defines a Java method that is accessed through rule resolution. By using rule resolution at run time, a function can express different behavior depending on the application ruleset list. You can invoke functions from expressions, from activities, and from Java.
Functions are defined within a library; both the library and its functions must be defined in the same ruleset. A Function rule defines the parameters and the Java code that is invoked when calling the function.
After you define a function, you can define one or more function aliases to customize the parameter descriptions and default values.
Pega Platform includes many predefined functions. To see if a function you need has already been defined, you can use the Expression Builder to list the functions that are defined in each library.