SEARCHFORMER: Semantic patent embeddings by siamese transformers for prior art search

The identification of relevant prior art for patent applications is of key importance for the work of patent examiners. The recent advancements in the field of natural language processing in the form of language models such as BERT enable the creation of the next generation of prior art search tools. These models can generate vectorial representations of input text, enabling the use of vector similarity as proxy for semantic text similarity. We fine-tuned a patent-specific BERT model for prior art search on a large set of real-world examples of patent claims, corresponding passages prejudicing novelty or inventive step, and random text fragments, creating the SEARCHFORMER. We show in retrospective ranking experiments that our model is a real improvement. For this purpose, we compiled an evaluation collection comprising 2014 pairs of patent application and related potential prior art documents. We employed two representative baselines for comparison: (i) an optimized combination of automatically built queries and the BM25 ranking function, and (ii) several state-of-the-art language models, including SentenceTransformers optimized for semantic retrieval. Ranking performance was measured as rank of the first relevant result. Using t-tests, we show that the achieved ranking improvements of the SEARCHFORMER over the baselines are statistically significant ($\alpha =0.01$).