This is a very, very common
type of construction in Bioconductor that has proven to be immensely powerful.
There's an obvious
generalization the expression set into something called an eSet.
And the difference between an expression set and
an eSet is that we don't have single expression matrix.
We have multiple matrices.
So what could that correspond to?
For example, it could correspond to a two
column micro experiment where each matrix is a column of the microarray.
Or it could correspond to data on say DNA methylation,
where one matrix corresponds to the methylation channel and
the other matrix correspond to the un-methylation channel.
