a use case single domain

[Ci98yr]

Greetings 

I need some pointers here; 'understand saml was set out
to solve inter domain user identity 

would like to gain some insights into applying for two different systems but belonging to the same domain

a) would this be a good solution at all based on saml
b) where does user id mapping logic resides (need to be developed separately ?) 

a sort of basic Qs ; many thanks in advance for pointers