Compact discs, DVDs: ions of Wikipedia articles have been published on optical discs. An English version, 2006 Wikipedia CD Selection, contained about 2,000 articles. The Polish-language version contains nearly 240,000 articles. T are German- and Spanish-language versions as well. Also, "Wikipedia for Schools", the Wikipedia series of CDs / DVDs produced by Wikipedians and SOS Children, is a , hand-ed, non-commercial selection from Wikipedia tared around the UK National Curriculum and intended to be useful for much of the English-speaking world. The project is available online; an equivalent print encyclopedia would require roughly 20 volumes. Printed books: T are efforts to put a select subset of Wikipedia's articles into printed book . Since 2009, tens of of print-on-demand books that reproduced English, German, Russian and French Wikipedia articles have been produced by the American company Books LLC and by three Mauritian sub sidiaries of the German publisher VDM. Semantic Web: The website DBpedia, begun in 2007, extracts data from the infoboxes and category declarations of the English-language Wikipedia. Wikimedia has created the Wikidata project with a similar objective of storing the basic facts from each page of Wikipedia and the other WMF wikis and make it available in a queriable semantic at, RDF. As of April 2021, it has 93,337,731 items. Obtaining the full contents of Wikipedia for reuse presents challenges, since direct cloning via a web crawler is discouraged. Wikipedia publishes "dumps" of its contents, but these are text-; as of 2007 t was no dump available of Wikipedia's images. Wikimedia Enterprise is a for-profit to this. Several languages of Wikipedia also maintain a reference desk, w volunteers answer questions from the general public. According to a study by Pnina Shachaf in the Journal of Documentation, the quality of the Wikipedia reference desk is comparable to a standa rd library reference desk, with an accuracy of 55 percent.Wikipedia's original was for users to re and edit content using any standard web browser through a fixed Internet connection. Although Wikipedia content has been ible through the mobile web since July 2013, The New York Times on February 9, 2014, d Erik Möller, deputy director of the Wikimedia Foundation, stating that the transition of internet traffic from desktops to mobile devices was significant and a cause for concern and worry. The article in The New York Times reported the comparison statistics for mobile edits stating that, " 20 percent of the reership of the English-language Wikipedia comes via mobile devices, a figure substantially lower than the percentage of mobile traffic for other media sites, many of which approach 50 percent. And the shift to mobile editing has lagged even more." The New York Times reports that Möller has assigned "a team of 10 software developers focused on mobile ", out of a total of approximately 200 employees working at the Wikimedia Foundation. One principal concern cited by The New York Times for the "worry" is for Wikipedia to effectively dress attrition issues with the number of editors which the online encyclopedia attracts to edit and maintain its content in a mobile environment. Bloomberg Businessweek reported in July 2014 that Google's Android mobile apps have dominated the largest share of global smart shipments for 2013 with 78.6% of market share over their next cst competitor in iOS with 15.2% of the market. At the time of the Tretikov appointment and her posted web interview with Sue Gardner in May 2014, Wikimedia representatives me a technical announcement concerning the number of mobile systems in the market seeking to Wikipedia. Directly after the posted web interview, the representatives stated that Wikimedia would be applying an all-inclusive approach to accommodate as many mobile systems as possible in its efforts for expanding general mobile , including BlackBerry and the dows system, making market share a secondary issue. The latest version of the Android app for Wikipedia was released on July 23, 2014, to generally positive reviews, scoring over four of a possible five in a poll of approximately 200,000 users downloing from Google. The latest version for iOS was released on April 3, 2013, to similar reviews.