You define a VB .NET external method using an operation with the <<External>> stereotype. External methods share the same properties as standard methods. You can also define the following specific properties for an external method:
Alias clause: you can use the Alias name extended attribute to specify numeric ordinal (prefixed by a @ character) or a name for an external method
Library clause: you can use the Library name extended attribute to specify the name of the external file that implements the external method
ANSI, Unicode and Automodifiers used for calling the external method can be defined using the Character set extended attribute of the external method