I saw an exact sequence of ideals
$0 \rightarrow I \cap J\rightarrow I \oplus J \rightarrow I + J \rightarrow 0$In this sequence, maps are ring homomorphisms or module homomorphisms?
And how the above sequence yield the exact seqeunce
$0 \rightarrow R/I \cap J\rightarrow R/I \oplus R/J \rightarrow R/(I + J) \rightarrow 0$