Every SYN corpus contains all the synchronic written corpora of the SYN series published up until the time of the given version's publication. The corpus SYN version 3 therefore contains the corpora SYN2000, SYN2005, SYN2006PUB, SYN2009PUB, SYN2010,SYN2013PUB and SYN2015; it additionally contains an as yet unpublished journalistic component predominantly from the years 2010–2014 in yearly volumes exceeding 200 mil. words.

Because all of these corpora are disjunctive (i.e. they do not contain the same texts), the total size of the SYN version 4 is given by their sum, which makes 3,626 billion words (tokens without punctuation). The SYN corpus is not representative; the dominant component is journalism, which is the result of the predominance of journalistic corpora SYN2006PUB, SYN2009PUB, SYN2013PUB and the journalistic component from the years 2010–2014.

The SYN version 4 corpus is referential,and will remain accessible to users even after newer versions have been published. It is however necessary to keep in mind that the linguistic information will become outdated, as a natural result of the referential nature of the corpus. Individual versions of the corpus SYN will continue to be published regularly every year with the addition of current journalistic data, and every new addition will be given the attribute value <doc syn> equal to the version of the SYN corpus in which the given text first appeared; for example a subcorpus corresponding to the above mentioned (as yet unpublished) journalistic component can be created from the SYN version 4 with the help of the condition syn="v4".

The composition of the journalistic part of the corpus SYN version 3 covers the production of most of the national daily newspapers (Mladá fronta DNES, Lidové noviny, Právo, Hospodářské noviny, Blesk, Sport), regional daily newspapers (chiefly Deníky Bohemia and Moravia published by Vltava Labe Media) and non-specialized magazines (Reflex, Respekt, Týden) fron the years 1998–2014; the total number of journalistic titles is 176. The following graphs show the composition of the SYN corpus based on the main text types over the years and offer a closer look at the composition of the journalistic section.

Composition of the corpus SYN version 4

Composition of the journalistic part of the corpus SYN version 4

The corpus SYN version 4 significantly differs from its predecessor, SYN version 3, in its structuring and annotation of texts which correspond with the corpus SYN2015. The changes are manifested in the adoption of the hierarchy of structural tags from SYN2015 (e.g. <opus> was replaced by <doc>, the paragraph <p> was newly introduced etc.) and their attributes (e.g. <opus name> was replaced by <doc title>), and also the classification of SYN2015 texts, which was retrospectively applied to all texts contained in the corpus SYN version 4. One of the results of this decision was also the exclusion of texts (predominantly online periodicals), which did not conform to the newly narrowed concept of written texts.

This correspondance to the corpus SYN2015 in structure and annotation has only two exceptions:

• the corpus SYN version 4 contains the additional attribute <doc syn> for the creation of subcorpora corresponding to the original reference corpora;
• a substantial change is the replacement of syntactic annotation in the corpus SYN2015 with a pilot version of phraseme annotation.

— Michal Křen, Olga Richterová