ch10-2 - Chapter 10 XML Introduction XML Extensible Markup...

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1 Chapter 10: XML Chapter 10: XML ©Silberschatz, Korth and Sudarshan 10.2 Database System Concepts Introduction Introduction ! XML: Extensible Markup Language ! Defined by the WWW Consortium (W3C) ! Originally intended as a document markup language not a database language " Documents have tags giving extra information about sections of the document # E.g. <title> XML </title> <slide> Introduction …</slide> " Derived from SGML (Standard Generalized Markup Language), but simpler to use than SGML " Extensible , unlike HTML # Users can add new tags, and separately specify how the tag should be handled for display " Goal was (is?) to replace HTML as the language for publishing documents on the Web
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2 ©Silberschatz, Korth and Sudarshan 10.3 Database System Concepts XML Introduction (Cont.) XML Introduction (Cont.) ! The ability to specify new tags, and to create nested tag structures made XML a great way to exchange data , not just documents. " Much of the use of XML has been in data exchange applications, not as a replacement for HTML ! Tags make data (relatively) self-documenting " E.g. <bank> <account> <account-number> A-101 </account-number> <branch-name> Downtown </branch-name> <balance> 500 </balance> </account> <depositor> <account-number> A-101 </account-number> <customer-name> Johnson </customer-name> </depositor> </bank> ©Silberschatz, Korth and Sudarshan 10.4 Database System Concepts XML: Motivation XML: Motivation ! Data interchange is critical in today’s networked world " Examples: # Banking: funds transfer # Order processing (especially inter-company orders) # Scientific data Chemistry: ChemML, … Genetics: BSML (Bio-Sequence Markup Language), … " Paper flow of information between organizations is being replaced by electronic flow of information ! Each application area has its own set of standards for representing information ! XML has become the basis for all new generation data interchange formats
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3 ©Silberschatz, Korth and Sudarshan 10.5 Database System Concepts XML Motivation (Cont.) XML Motivation (Cont.) ! Earlier generation formats were based on plain text with line headers indicating the meaning of fields " Similar in concept to email headers " Does not allow for nested structures, no standard “type” language " Tied too closely to low level document structure (lines, spaces, etc) ! Each XML based standard defines what are valid elements, using " XML type specification languages to specify the syntax # DTD (Document Type Descriptors) # XML Schema " Plus textual descriptions of the semantics ! XML allows new tags to be defined as required " However, this may be constrained by DTDs ! A wide variety of tools is available for parsing, browsing and querying XML documents/data ©Silberschatz, Korth and Sudarshan 10.6 Database System Concepts Structure of XML Data Structure of XML Data ! Tag : label for a section of data ! Element : section of data beginning with < tagname > and ending with matching </ tagname > ! Elements must be properly
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ch10-2 - Chapter 10 XML Introduction XML Extensible Markup...

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