So how does a technomancer build a database, internal or external (honestly there is no functional difference between these things) with threading? A data base is a storehouse of information, raw data. If the technomancer doesnt have that information where does it come from when threading or building a complex form? Everything they build comes from within their own minds
Existing CFs that use "databases" as per your claim:
Analyze
Exploit
Decrypt - oh, I especially reference decrypt:
Decrypt programs are designed to conduct a number of cipher-busting attacks—from pattern analysis to brute-force dictionary assaults to sophisticated mathematical tricks—to break into an encrypted system or service.
Those are the ones clearly need a long list of possible data on which to build - a dataabase. "A data base is a storehouse of information, raw data. If the technomancer doesnt have that information where does it come from when threading or building a complex form? Everything they build comes from within their own mind."
Where is the technomancer sustaining the database of cipher-busting attacks?
Where is the technomancer getting the database of security flaws and weaknesses?
Where is the database of registries, icon functions and types, program types, and so on that are necessary for Analyze to do a matrix perception report?
Saying a CF can't do that flies in the face of the fact that some CFs do, indeed, do that. It is the same reason saying it can't act as an interpreter between a set of sensors and the user fails.
The only valid reason is that the rulebook says it is optional, and it is an option you choose to not use. As I said, I happen to accept that reason from you for your game.