Of the university or college libraries, the collections of Peking University and Zhejiang University libraries lead the nation. The national library network also includes scientific research institution libraries, trade union libraries, plus libraries and reading rooms attached to government institutions, army units, primary and secondary schools, townships, enterprises and local communities. The country's main library, the National Library of China, housed a rich collection of books, periodicals, newspapers, maps, prints, photographs, manuscripts, microforms, tape recordings, and inscriptions on bronze, stone, bones, and tortoiseshells. The National Library of China, with a collection of over 26 million volumes, is the largest library in Asia, housing the largest collection of Chinese books in the world. In the library's collection are over 35,000 oracle bones and tortoise shells carved with ancient Chinese characters, 1.6 million volumes of traditional thread-bound books, over 16,000 volumes of documents from Dunhuang Grottoes, 12 million volumes of foreign-language books, and dozens of electronic databases. The library started to accept the submissions of official national publications in 1916, becoming the main national database; and began to accept submissions of domestic electronic publications in 1987. It is also the country's ISSN (International Standard Serial Number) Center and Network Information Center. At present, the National Library of China has formed a digital library alliance with some 90 other libraries around the country, making joint efforts in promoting the development and application of China's digital public information service. The second phase of the National Library – China Digital Library, whose foundation was laid at the end of 2004, is planned to be completed and commissioned in October 2007. The expanded library will be able to meet book storage demand for the next 30 years. The Digital Library will make it the world's biggest Chinese literature collection center and digital resources base, as well as the most advanced network service base in China. The Shanghai Municipal Library, one of the largest public libraries in the country, contained over 7 million volumes, nearly 1 million of which were in foreign languages. The Shanghai Library, well known at home and abroad, is China's largest provincial-level library. Of its collection, the over 1.7 million volumes of ancient documents are the most valuable and representative, including 25,000 titles of rare ancient books in 178,000 volumes, many being the only copies extant in the world. The oldest document dates back nearly 1,500 years. The Peking University Library took over the collections of the Yanjing University Library in 1950 and by the mid-1980s – with more than 3 million volumes, one-fourth of them in foreign languages – was one of the best university libraries in the country.