These are SQL User Defined Functions (UDFs). They reside in the SQL database where they are used. This functionality is available in many of the database platforms that Xtraction supports. You can do an Internet search to find information regarding creating UDFs for your specific database platforms.
A quick search turned up this page, which should be a good starting point for MSSQL UDFs: Create User-defined Functions (Database Engine)
The specific functions you referenced, as well as most UDFs we create for Xtraction, are scalar functions. They take in 1 or more parameters, perform some calculation, and then return a single value.
I hope this helps. Let me know if you have any additional questions.