  Extracting tables from documents is a crucial task in any document conversion
pipeline. Recently, transformer-based models have demonstrated that
table-structure can be recognized with impressive accuracy using
Image-to-Markup-Sequence (Im2Seq) approaches. Taking only the image of a table,
such models predict a sequence of tokens (e.g. in HTML, LaTeX) which represent
the structure of the table. Since the token representation of the table
structure has a significant impact on the accuracy and run-time performance of
any Im2Seq model, we investigate in this paper how table-structure
representation can be optimised. We propose a new, optimised table-structure
language (OTSL) with a minimized vocabulary and specific rules. The benefits of
OTSL are that it reduces the number of tokens to 5 (HTML needs 28+) and
shortens the sequence length to half of HTML on average. Consequently, model
accuracy improves significantly, inference time is halved compared to
HTML-based models, and the predicted table structures are always syntactically
correct. This in turn eliminates most post-processing needs.
