Abstract: In this paper, we present a corpus for use in automatic readability assessment and automatic text simplification of German. The corpus is compiled from web sources and consists of approximately 211,000 sentences. As a novel contribution, it contains information on text structure, typography, and images, which can be exploited as part of machine learning approaches to readability assessment and text simplification. The focus of this publication is on representing such information as an extension to an existing corpus standard.

Introduction: Simplified language is a variety of standard language characterized by reduced lexical and syntactic complexity, the addition of explanations for difficult concepts, and clearly structured layout. Among the target groups of simplified language commonly mentioned are persons with cognitive impairment or learning disabilities, prelingually deaf persons, functionally illiterate persons, and foreign language learners BIBREF0. Two natural language processing tasks deal with the concept of simplified language: automatic readability assessment and automatic text simplification. Readability assessment refers to the process of determining the level of difficulty of a text, e.g., along readability measures, school grades, or levels of the Common European Framework of Reference for Languages (CEFR) BIBREF1. Readability measures, in their traditional form, take into account only surface features. For example, the Flesch Reading Ease Score BIBREF2 measures the length of words (in syllables) and sentences (in words). While readability has been shown to correlate with such features to some extent BIBREF3, a consensus has emerged according to which they are not sufficient to account for all of the complexity inherent in a text. As [p. 2618]kauchak-et-al-2014 state, “the usability of readability formulas is limited and there is little evidence that the output of these tools directly results in improved understanding by readers”. Recently, more sophisticated models employing (deeper) linguistic features such as lexical, semantic, morphological, morphosyntactic, syntactic, pragmatic, discourse, psycholinguistic, and language model features have been proposed BIBREF4, BIBREF5, BIBREF6, BIBREF7, BIBREF8. Automatic text simplification was initiated in the late 1990s BIBREF9, BIBREF10 and since then has been approached by means of rule-based and statistical methods. As part of a rule-based approach, the operations carried out typically include replacing complex lexical and syntactic units by simpler ones. A statistical approach generally conceptualizes the simplification task as one of converting a standard-language into a simplified-language text using machine translation. nisioi-et-al-2017 introduced neural machine translation to automatic text simplification. Research on automatic text simplification is comparatively widespread for languages such as English, Swedish, Spanish, and Brazilian Portuguese. To the authors' knowledge, no productive system exists for German. suter-2015, suter-et-al-2016 presented a prototype of a rule-based system for German. Machine learning approaches to both readability assessment and text simplification rely on data systematically prepared in the form of corpora. Specifically, for automatic text simplification via machine translation, pairs of standard-language/simplified-language texts aligned at the sentence level (i.e., parallel corpora) are needed. The paper at hand introduces a corpus developed for use in automatic readability assessment and automatic text simplification of German. The focus of this publication is on representing information that is valuable for these tasks but that hitherto has largely been ignored in machine learning approaches centering around simplified language, specifically, text structure (e.g., paragraphs, lines), typography (e.g., font type, font style), and image (content, position, and dimensions) information. The importance of considering such information has repeatedly been asserted theoretically BIBREF11, BIBREF12, BIBREF0. The remainder of this paper is structured as follows: Section SECREF2 presents previous corpora used for automatic readability assessment and text simplification. Section SECREF3 describes our corpus, introducing its novel aspects and presenting the primary data (Section SECREF7), the metadata (Section SECREF10), the secondary data (Section SECREF28), the profile (Section SECREF35), and the results of machine learning experiments carried out on the corpus (Section SECREF37).

Question: Which information about text structure is included in the corpus?
Answer: paragraph, lines, textspan element (paragraph segmentation, line segmentation, Information on physical page segmentation(for PDF only))