Can strong structural encoding reduce the importance of Message Passing?
Floor Eijkelboom Erik Bekkers Michael Bronstein Francesco Di Giovanni
The most prevalent class of neural networks operating on graphs are message
passing neural networks (MPNNs), in which the representation of a node is
updated iteratively by aggregating information in the 1-hop neighborhood. Since
this paradigm for computing node embeddings may prevent the model from learning
coarse topological structures, the initial features are often augmented with
structural information of the graph, typically in the form of Laplacian
eigenvectors or Random Walk transition probabilities. In this work, we explore
the contribution of message passing when strong structural encodings are
provided. We introduce a novel way of modeling the interaction between feature
and structural information based on their tensor product rather than the
standard concatenation. The choice of interaction is compared in common
scenarios and in settings where the capacity of the message-passing layer is
severely reduced and ultimately the message-passing phase is removed
altogether. Our results indicate that using tensor-based encodings is always at
least on par with the concatenation-based encoding and that it makes the model
much more robust when the message passing layers are removed, on some tasks
incurring almost no drop in performance. This suggests that the importance of
message passing is limited when the model can construct strong structural
encodings.