  Graph databases (GDBs) enable processing and analysis of unstructured,
complex, rich, and usually vast graph datasets. Despite the large significance
of GDBs in both academia and industry, little effort has been made into
integrating them with the predictive power of graph neural networks (GNNs). In
this work, we show how to seamlessly combine nearly any GNN model with the
computational capabilities of GDBs. For this, we observe that the majority of
these systems are based on, or support, a graph data model called the Labeled
Property Graph (LPG), where vertices and edges can have arbitrarily complex
sets of labels and properties. We then develop LPG2vec, an encoder that
transforms an arbitrary LPG dataset into a representation that can be directly
used with a broad class of GNNs, including convolutional, attentional,
message-passing, and even higher-order or spectral models. In our evaluation,
we show that the rich information represented as LPG labels and properties is
properly preserved by LPG2vec, and it increases the accuracy of predictions
regardless of the targeted learning task or the used GNN model, by up to 34%
compared to graphs with no LPG labels/properties. In general, LPG2vec enables
combining predictive power of the most powerful GNNs with the full scope of
information encoded in the LPG model, paving the way for neural graph
databases, a class of systems where the vast complexity of maintained data will
benefit from modern and future graph machine learning methods.
