  Label scarcity is a bottleneck for improving task performance in specialised
domains. We propose a novel compositional transfer learning framework (DoT5 -
domain compositional zero-shot T5) for zero-shot domain transfer. Without
access to in-domain labels, DoT5 jointly learns domain knowledge (from MLM of
unlabelled in-domain free text) and task knowledge (from task training on more
readily available general-domain data) in a multi-task manner. To improve the
transferability of task training, we design a strategy named NLGU: we
simultaneously train NLG for in-domain label-to-data generation which enables
data augmentation for self-finetuning and NLU for label prediction. We evaluate
DoT5 on the biomedical domain and the resource-lean subdomain of radiology,
focusing on NLI, text summarisation and embedding learning. DoT5 demonstrates
the effectiveness of compositional transfer learning through multi-task
learning. In particular, DoT5 outperforms the current SOTA in zero-shot
transfer by over 7 absolute points in accuracy on RadNLI. We validate DoT5 with
ablations and a case study demonstrating its ability to solve challenging NLI
examples requiring in-domain expertise.
