How does a search engine find a dynamic URL address that's based on values in a DB?

[eluser]Dandy_andy[/eluser]
No you understood correctly and I thought the answer would be something like that. I haven't built my dynamic structure yet - I'm just playing around with it and I was just curious to know. So does the dynamic system need to address the fact that search engines will search for the information? Or do I just assume that as long as the data exists and a particular dynamic page extracts and processes information from my DB, a search engine will also find it? Do I work on the basis that if I can type it into the URL address bar and it produces a page, google will find ti? I'm quite amazed at how this all works and I'll try and explain my thinking...

Suppose I have dynamically created pages called

www.domain.com/profile/member1
www.domain.com/profile/member5
www.domain.com/profile/member6
www.domain.com/profile/member7
www.domain.com/profile/member8 etc.

How does google know that member2 doesn't exist for example? Or how does it know that something completely different like abcdefg123 doesn't exist? Does it actually search for every possible dynamic variation or does something tell google which dynamic addresses are possible?