Our motivation is to build a systematic method in order to investigate the
structure of cluster algebras of geometric type.
The method is given through the notion of mixing-type sub-seeds, the theory
of seed homomorphisms and the view-point of gluing of seeds. As an application,
for (rooted) cluster algebras, we completely classify rooted cluster
subalgebras and characterize rooted cluster quotient algebras in detail. Also,
we build the relationship between the categorification of a rooted cluster
algebra and that of its rooted cluster subalgebras.
Note that cluster algebras of geometric type studied here are of the
sign-skew-symmetric case.Comment: 41 page