variety of subjects, specialising among other things in editing reference works, including (as author) the Cambridge Encyclopedia of Language (1987, 1997, 2010) and the Cambridge Encyclopedia of the English Language (1995, 2003, 2019), and (as editor) the Cambridge Biographical Dictionary, the Cambridge Factfinder, the Cambridge Encyclopedia, and the New Penguin Encyclopedia (2003). He has also written plays and poetry. He has published several books for the general reader about linguistics and the English language, which use varied graphics and short essays to communicate technical material in an accessible manner. In his article "What is Standard English", Crystal hypothesises that, globally, English will both split and converge, with local variants becoming less mutually comprehensible and therefore necessitating the rise of what he terms World Standard Spoken English (see also International English). In his 2004 book The Stories of English, a general history of the English language, he describes the value he sees in linguistic diversity and the according of respect to varieties of English generally considered "non-standard". In 2009 Routledge published his autobiographical memoir Just a Phrase I'm Going Through: My Life in Language, which was released simultaneously with a DVD of three of his lectures. His book Spell It Out: The Curious, Enthralling and Extraordinary Story of English Spelling (2013) explains why some English words are difficult to spell. His companion book, Making a Point: The Pernickety Story of English Punctuation came out in 2015 from Profile Books (UK) and St. Martin's Press (USA). Crystal is a proponent of a new field of study, Internet linguistics, and has published Language and the Internet (2001) on the subject. Crystal's book Txtng: The Gr8 Db8 (2008) focused on text language and its impact on society. He was one of the book series editors of The Language Library. From 2001 to 2006, Crystal served as the Chairman of Crystal Reference Systems Limited, a provider of reference content and Internet search and advertising technology. The company's iSense and Sitescreen products are based upon the patented Global Data Model, a complex semantic network that Crystal devised in the early 1980s and was adapted for use on the Internet in the mid 1990s. These include semantic targeting technology (marketed as iSense by ad pepper media) and brand protection technology (marketed as SiteScreen by Emediate ApS). The iSense technology is the subject of patents in the United Kingdom and the United States. After the company's acquisition by