DE plain: A G erman Parallel Corpus with Intralingual Translations into Plain Language for Sentence and Document Simplification (2023)

Abstract: Text simplification is an intralingual translation task in which documents, or sentences of a complex source text are simplified for a target audience. The success of automatic text simplification systems is highly dependent on the quality of parallel data used for training and evaluation. To advance sentence simplification and document simplification in German, this paper presents DEplain, a new dataset of parallel, professionally written and manually aligned simplifications in plain German “plain DE” or in German: “Einfache Sprache”. DEplain consists of a news-domain (approx. 500 document pairs, approx. 13k sentence pairs) and a web-domain corpus (approx. 150 aligned documents, approx. 2k aligned sentence pairs). In addition, we are building a web harvester and experimenting with automatic alignment methods to facilitate the integration of non-aligned and to be-published parallel documents. Using this approach, we are dynamically increasing the web-domain corpus, so it is currently extended to approx. 750 document pairs and approx. 3.5k aligned sentence pairs. We show that using DEplain to train a transformer-based seq2seq text simplification model can achieve promising results. We make available the corpus, the adapted alignment methods for German, the web harvester and the trained models here: https://github.com/rstodden/DEPlain .

## introduction automatic text simplification (ts) is the process of automatically generating a simpler version of complex texts while preserving the main information @xcite . current ts research mostly focuses on english and on sentencelevel simplification. this paper contributes to ts research on german. compared to other european languages, german is more difficult to read due to complex sentence structures and many compound words @xcite . according to @xcite , roughly 6.2 mio. adults in germany (approx. 12.1%) have reading and writing problems on the character-level (0.6%), word-level (approx. 3.4%) or sentence-level (approx. 8.1%). to counteract and make texts accessible to more people, currently two dominant german variants for simplified language exist (maaß, 2020): this is also reflected in a rise in research and application of manual and automatic german text simplification: i) many german web pages are provided in standard german as well as in plain or easy-to-read german, e.g., apotheken umschau foot_0 or the german federal agency for food foot_1 , ii) news agencies are publishing their news in plain or easyto-read german, e.g., austrian press agency foot_2 or deutschlandfunk foot_3 . @xcite were the first who made use of these resources for supervised, automatic german ts. they created a small parallel corpus of approx. 250 web pages with intralingual translations from standard german to easy-to-read ger-man. however, due to copyright issues, they (and also its extension by @xcite ) could not make their corpus publicly available. to avoid such problems, @xcite ; @xcite built ts corpora based on open accessible wikipedia texts simplified for children. due to the high cost of manual sentence-wise alignment or not applicable automatic alignment methods @xcite , these corpora are only aligned on the document level. furthermore, @xcite report results on experiments with some existing automatic alignment methods and show non-satisfying, error-prone results. in this work, we tackle some of the named problems by proposing, deplain, a new parallel german corpus for text simplification with manual and automatic alignments on the document and sentence level. deplain contains intralingual translations mostly into plain german and includes "strong" as well as "mild" simplifications. overall, we propose 4 subcorpora with in total 1,239 document pairs, 14,968 manual sentencewise alignments and 1,594 automatic sentence-wise alignments. one subcorpus is built from professionally simplified news articles in plain language of the austrian press agency foot_4 . the resources of the other 3 subcorpora are compiled by a new web harvester, making use of publicly available parallel documents. we analyze these subcorpora based on human ratings and annotations to get more insights into the quality and the simplification processes within the data. we further show two use cases of our new ts corpus: i) evaluating automatic alignment methods, and ii) exemplifying ts training and evaluation with deplain. our data, web harvester, code for alignment methods and models are publicly available (with some restrictions). german corpora were also proposed in recent years, both on either document level (e.g., lexikacorpus @xcite or sentence-level (e.g., web-corpus, apa-lha, capito-corpus @xcite , but not focussing on both levels 7 . unfortunately, many of the datasets cannot be used for training ts models or only with caution because, for example, i) they are too small for training (e.g., @xcite ), ii) they are automatically aligned with questionable quality (e.g., @xcite , iii) are only available for evaluation (e.g., @xcite , iv) they are not truly parallel as the complex and simple versions are written independently (e.g., aumiller and gertz 2022), or v) are not available (e.g., @xcite ) sometimes due to copyright issues (e.g., @xcite . deplain tackles all of the mentioned problems, i.e., size, alignment quality, simplification quality, and availability. alignment methods and web scraping are already used to overcome some of these issues. for example, similar to our work, @xcite present a web scraper to scrape parallel documents from the web and automatically align them. however, @xcite have shown that automatic sentence alignment is still an open challenge for german by comparing some existing alignment methods. in this work, we will evaluate the alignment methods on our manually aligned data and will adapt them for our purpose, e.g., use german resources and incorporate n:m alignments. ## document-level ts corpora we present two new ts corpora on the document level, deplain-apa and deplain-web, containing parallel documents in standard german and plain german. ## sentence-level ts corpora we aligned both corpora, deplain-apa and deplain-web, also on the sentence level. all 483 available parallel documents of deplain-apa and 147 documents of deplain-web are manually aligned on the sentence level with the assistance of a ts annotation tool. overall, 14,968 sentence pairs of 630 document pairs are manually aligned. we first describe the annotation procedure (see subsection 4.1) and the resulting statistics per subcorpus (subsection 4.2 and subsection 4.3). ## automatic sentence-wise alignment to exemplify the usage of the manual alignments and to provide sentence-wise alignments for the unaligned documents of deplain-web we evaluate different alignment algorithms on the manually aligned data. ## automatic text simplification to exemplify the usage of deplain for training and evaluating ts models, we are presenting results on finetuning long-mbart on our documentlevel corpus as well as finetuning mbart on our sentence-level corpus, using code provided by @xcite 21 . ## conclusion and future work in this paper, we have introduced a new german corpus for text simplification, called deplain. the corpus contains data for document simplification as well as sentence simplification of news (deplain-apa) and web data (deplain-web). the major part of the sentence-wise alignments are manually aligned and a part of it is also manually analyzed. the analysis shows that the subcorpus deplain-apa contains rather mild simplifications whereas deplain-web contains rather strong simplifications. however, for both corpora, a large variety of simplification operations were identified. furthermore, we evaluated automatic sentence alignment methods on our manually aligned data. in our experiments, massalign got the best results but it has only identified a few n:m alignments (where @xmath0. one direction for future work is to further investigate n:m alignments algorithms for ts corporaand include paragraphs into the automatic alignment process. we also showed first promising experiments on sentence and document simplification. however, these are just simple benchmarks and have only been evaluated with automatic metrics yet. in future work, the results should be verified by manual evaluation and could be improved by using more sophisticated approaches. finally, we think that deplain can boost and improve the research in german text simplification, to make more complex texts accessible to people with reading problems.