Please check the explanation below, Let us know if you have further inquiries.

This activity is used to define a default data generator which will insert default (predefined) values or modify data when creating, modifying or deleting a design object or design part. Default values are created in a special package (API Packages) that is written expressly for this purpose. Default data generators are defined with a business object type (e.g., Object, Design Part), a Key (a concatenated value of all Plant Classes and Plant Standards), and an Implementation Package (A package, e.g., TEST_API containing commands such as Pre-insert, Pre-new, Post-new, Pre-delete, Post-insert, among others).

For example, Every new design object created from ‘Pump Centrifugal” class, is added  the ‘centrifugal pump’ text in the Object Description field.

Documented here:

https://docs.ifs.com/ifsclouddocs/23r1/AssetDesignBasics/AboutDefaultDataGen.htm?StandAlone=true