  We introduce the notion of an online matroid embedding, which is an algorithm
for mapping an unknown matroid that is revealed in an online fashion to a
larger-but-known matroid. The existence of such embedding enables a reduction
from the version of the matroid secretary problem where the matroid is unknown
to the version where the matroid is known in advance. We show that online
matroid embeddings exist for binary (and hence graphic) and laminar matroids.
We also show a negative result showing that no online matroid embedding exists
for the class of all matroids. Finally, we define the notion of an approximate
matroid embedding, generalizing the notion of {\alpha}-partition property, and
provide an upper bound on the approximability of binary matroids by a partition
matroid, matching the lower bound of Dughmi et al.
