External routines are routines that have their logic implemented in a programming language application that resides outside of the database, in the file system of the database server.
The association of the routine with the external code application is asserted by the specification of the EXTERNAL clause in the CREATE statement of the routine.
You can create external procedures, external functions, and external methods. Although they are all implemented in external programming languages, each routine functional type has different features. Before deciding to implement an external routine, it is important that you first understand what external routines are, and how they are implemented and used, by reading the topic, "Overview of external routines". With that knowledge you can then learn more about external routines from the topics targeted by the related links so that you can make informed decisions about when and how to use them in your database environment.