how can I make sure a given field is available for a given source type?

[mcbradford]

I am using the following within a search to create a field called link.

eval link=uri_scheme+"://"+dest_host+uri_path

I really just want the field to be an available field for the sourcetype. Is this possible, and if yes how?

[martin_mueller]

You're looking for calculated fields.

http://docs.splunk.com/Documentation/Splunk/5.0/Knowledge/definecalcfields