  As privacy protection receives much attention, unlearning the effect of a
specific node from a pre-trained graph learning model has become equally
important. However, due to the node dependency in the graph-structured data,
representation unlearning in Graph Neural Networks (GNNs) is challenging and
less well explored. In this paper, we fill in this gap by first studying the
unlearning problem in linear-GNNs, and then introducing its extension to
non-linear structures. Given a set of nodes to unlearn, we propose PROJECTOR
that unlearns by projecting the weight parameters of the pre-trained model onto
a subspace that is irrelevant to features of the nodes to be forgotten.
PROJECTOR could overcome the challenges caused by node dependency and enjoys a
perfect data removal, i.e., the unlearned model parameters do not contain any
information about the unlearned node features which is guaranteed by
algorithmic construction. Empirical results on real-world datasets illustrate
the effectiveness and efficiency of PROJECTOR.

Machine Learning;Artificial Intelligence