## 4 Results and Discussion
### What open challenges does prior art patent search and retrieval face? Numerous studies have identified several key challenges in prior art searches and patent retrieval, as summarized in Table 10 from the analysis of the 78 articles. A primary concern is the 'inconsistent document structure and formats' [42, 59, 60, 63, 71, 72, 85, 89, 93, 107], across patents. This inconsistency complicates retrieval due to the blend of structured and unstructured sections, diverse formats, and multiple languages. These variations stem from the nature of patent filings, which must accommodate a wide range of innovations and legal requirements across different jurisdictions. This leads to variations in how information is organized and presented, including differences in the use of structured (e.g., claims, abstracts) and unstructured (e.g., descriptions, drawings) sections, and the acceptance of documents in various formats and languages to suit international standards and applicent preferences. These variations pose challenges for retrieval systems in effectively interpreting the diverse content. Another significant obstacle is the'sophisticated patent language and vocabulary' [44, 47, 69, 70, 87, 88, 96, 109], which arises from the need for precise descriptions and claims of innovation. The use of intricate technical, legal, and domain-specific terms aims for legal accuracy but introduces complexity in the retrieval process. Search systems must interpret and match the nuanced vocabulary used in patents, which is compounded by the vast array of patent documents across different jurisdictions with varying requirements and languages requiring translation. The challenge of accurately parsing and understanding this intricate language underscores the need for retrieval techniques sophisticated enough to effectively handle these linguistic complexities. Several researchers have also reported 'query reduction and query expansion' to disambiguate the query as a significant challenge for patent retrieval [39, 61, 62, 74, 78, 107]. Patent documents are inherently complex due to their lengthy nature and extensive use of technical and specialized terminology. Accurately capturing the query's requirements and goals is crucial to retrieving the most relevant patent documents. Therefore, researchers have developed techniques to disambiguate the query, sometimes by reducing the query to remove irrelevant and noisy terms, and sometimes by expanding the query to add more relevant keywords using known external sources. Researchers must strike a balance \begin{table}
\begin{tabular}{l c} \hline \hline \multicolumn{1}{c}{**Challenges**} & **Studies** \\ \hline Commercial patent analysis & [115] \\ \hline Sophisticated patent language and vocabulary & [44, 47, 69, 70, 87, 88, 96, 109] \\ \hline Term mismatch & [44, 46, 61, 73, 78, 94, 113] \\ \hline Information asymmetry and overload & [47, 63, 68, 75, 92, 93] \\ \hline Query reduction/expansion and query disambiguation & [39, 61, 62, 74, 78, 107] \\ \hline Inconsistent document structure and formats & [42, 59, 60, 63, 71, 72, 85, 89, 93, 107] \\ \hline Finding the most relevant classification codes & [117] \\ \hline Large quantity of patent applications & [56, 89] \\ \hline Requirement of a high recall & [39, 50, 66, 89, 107] \\ \hline Limitations of keyword-based search & [66, 114] \\ \hline Lack of data for training BERT & [44] \\ \hline Retrieval results accuracy and efficiency & [57, 84, 111] \\ \hline Examiner citations recommendation problem & [81] \\ \hline Patent Ranking & [75] \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Summary of the challenges that prior art searches have to face. between oversimplification and adding complexity to the query to enhance the patent retrieval results. 'Term mismatch' is another crucial challenge [44; 46; 61; 73; 78; 94; 113], with researchers addressing the impact of semantic and conceptual variation as well as multilingual complexities on patent retrieval.