A computer identifies a relationship among a subset of a set of data blocks, a basis of the relationship forming a context shared by the subset of data blocks. The computer selects a code data structure from a set of code data structures using the context. The context is associated with the code data structure, and the code data structure includes a set of codes. The computer computes, for a first data block in the subset of data blocks, a first code corresponding to a content of the first data block. The computer determines whether the first code matches a stored code in the code data structure. The computer replaces, responsive to the first code matching the stored code, the first data block with a reference to an instance of the first data block. The computer causes the reference to be stored in a target data processing system.