  The entanglement wedge reconstruction paradigm in AdS/CFT states that for a
bulk qudit within the entanglement wedge of a boundary subregion $\bar{A}$,
operators acting on the bulk qudit can be reconstructed as CFT operators on
$\bar{A}$. This naturally fits within the framework of quantum error
correction, with the CFT states containing the bulk qudit forming a code
protected against the erasure of the boundary subregion $A$. In this paper, we
set up and study a framework for relational bulk reconstruction in holography:
given two code subspaces both protected against erasure of the boundary region
$A$, the goal is to relate the operator reconstructions between the two spaces.
To accomplish this, we assume that the two code subspaces are smoothly
connected by a one-parameter family of codes all protected against the erasure
of $A$, and that the maximally-entangled states on these codes are all
full-rank. We argue that such code subspaces can naturally be constructed in
holography in a "measurement-based" setting. In this setting, we derive a flow
equation for the operator reconstruction of a fixed code subspace operator
using modular theory which can, in principle, be integrated to relate the
reconstructed operators all along the flow. We observe a striking resemblance
between our formulas for relational bulk reconstruction and the infinite-time
limit of Connes cocycle flow, and take some steps towards making this
connection more rigorous. We also provide alternative derivations of our
reconstruction formulas in terms of a canonical reconstruction map we call the
modular reflection operator.
