[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: The meaning of the "string" datatype?
Somewhere in the comp-text-sgml list is an email from Erik Naggum that goes something like, "Then Eliot explained SGML to me and I realized, it's a string." Is it an anti-data type? In the sense that data type means predictable, yes. In the sense that it could mean "meaningful", no. Characters in practice/use have frequencies and cluster in groups. So DTDs. DTDs do not data type strings as much as they label them. We use DTDs because of the user. Schemas? User input frequencies are paired with data storage frequencies. Frequencies from different sources tend to mud. We have strings because of the user. Is a user a data type? len -----Original Message----- From: Rick Jelliffe [mailto:rjelliffe@a...] Sent: Wednesday, April 15, 2009 8:21 AM To: xml-dev@l... Subject: Re: The meaning of the "string" datatype? Costello, Roger L. wrote: > > The content of <Author> can be characters from any language - English, Chinese, Arabic, Italian, Greek, German, Spanish, Russian, etc - plus punctuation symbols plus math symbols. If I did my arithmetic correctly [1], the total number of different characters is: 1,112,000. > Strictly, languages don't have characters, they have writing systems, and writing systems use scripts, and scripts are made from characters. Furthermore, Unicode has Private Use Areas which allow non-standard characters to be represented. XML Schemas String datatype is perhaps better thought of as an anti-datatype rather than a datatype. What it does is signify an absence of a value-space: it is not asserted to be a number, not asserted to be a date, not asserted to be a boolean. This is of course a little topsy turvy. I had a case with an insurance company who received data from the agents which had standard fields but the fields could contain any notation. There was a separate process where people would check the fields and "re-work" them into the standard notations. So the input might have <date>20th May, 2010</date> and after rework it would contain <date>2010-05-20</date> They were surprised to learn that they could not merely say that the incoming data was a string, and then restrict this string to be a date type. (Since xs:date is not a restriction of xs:string.) The original XML Schemas datatype hierarchy was not designed with document refinement in mind (i.e. marking up the document, passing it as text through several different XML stages): the design only makes sense if you assume that the data is living in a DBMS, i.e. where the types are actually primitive storage types for DBMS. Cheers Rick Jelliffe _______________________________________________________________________ XML-DEV is a publicly archived, unmoderated list hosted by OASIS to support XML implementation and development. To minimize spam in the archives, you must subscribe before posting. [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ Or unsubscribe: xml-dev-unsubscribe@l... subscribe: xml-dev-subscribe@l... List archive: http://lists.xml.org/archives/xml-dev/ List Guidelines: http://www.oasis-open.org/maillists/guidelines.php
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