《Table 1 Examples of the rules for extracting soil variables1)》

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《Automatic extraction and structuration of soil–environment relationship information from soil survey reports》

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1) prefix，prefix of value；suffix，suffix of value；m，number；q，quantifier；wp，punctuation；“.”，any string；“*”，the frequency of 0 or more occurrences.

In this paper，the CRF++（http://taku910.github.io/crfpp）open source software was used to construct the CRFs model.As shown in Fig.4，the CRFs model is a supervised learning method，so it needs training before application.The commonly used training inputs for CRF++include training files and feature templates.An example of a training file is shown in Table 2:the first three columns are word，part-of-speech and K value.“Word”is the result of word segmentation and the carrier of other information，and part-of-speech is the basic grammatical attributes of words（Bird et al.2009）.Both word and part-of-speech reflect the characteristics of linguistics.The K value is Boolean and stands for whether the current word is in the keyword dictionary，so it embodies the semantic information.The fourth column contains the tags represented in BIO format，which indicates the variable the word belongs to.For example，PM denotes parent material，and the tags B，I，E，and O denote the beginning，inside，ending and out of a variable value entity.B-PM means the current word is the beginning of the parent material value.