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Schema

Schema. Schemas specify the structure of an XML document constraints on its content This is also the purpose of a DTD schema does it better syntax is XML can use existing XML tools. Schema. What you can't do with DTD's constrain the #PCDATA e.g. a telephone number a price

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Schema

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  1. Schema • Schemas • specify the structure of an XML document • constraints on its content • This is also the purpose of a DTD • schema does it better • syntax is XML • can use existing XML tools

  2. Schema • What you can't do with DTD's • constrain the #PCDATA e.g. • a telephone number • a price • a single word • precisely constrain repetition • up to three children on a family ticket • a precise selection of elements • in any combination or permutation

  3. Schema • XML is a meta-language for defining tag languages • A schema is a formal specification (in XML) of the grammar for one language • useful for validating content & interchange • XML Schema is a language for writing the specifications

  4. Schemas • Common Vocabularies • Shared Applications • Network effect • Formal Sets of Rules • Machine-based XML processing • Not human-based document processing • Building Contracts • Core rules for a series of transactions

  5. Schemas • DTDs • good at describing documents • can't manage complex data structures • syntax is not extensible • available tools won't work

  6. Schemas • Schemas build on primitive types • integers, floating point, strings, dates • Types can be based on other types • aggregations • specifications • restrictions • equivalences • Distinction between types and elements

  7. Schemas • Schema building is very like • OO data design • E-R diagrams • Schemas may be complex compared to the documents • because humans 'intuitively understand' tag names

  8. Schema Standards • XML Schema (current W3C standard) • large, full-featured, unimplemented • XML-Data • early contender, supported by Microsoft • reduced set of XML-Data is part of IE5. • DCD • joint creation of Microsoft and IBM • simpler version of XML-Data

  9. Schema Standards • SOX • XML structures via OO-inheritance • Schematron • uses XSLT for schemas • DSD • like Schematron with simpler XML syntax • RELAX • based on hedge automata theory • much simpler than XML Schema

  10. Schema History

  11. Schema Problems • Legal implications of schemas as contracts • Eskimo Snow and Scottish Rain:Legal Considerations of Schema Design • http://www.w3.org/TR/md-policy-design • syntactic operability with semantic fault • occurs because DTDs and schemas mix • syntax • semantics

  12. Schema Problems • W3C standard "XML Schemas" • Too big, too complex • XML 1.0 spec = 30 pages, Schemas >200 • Too much, too soon • it isn't clear that many developers are sure what to do with this enormous toolkit today. • Competitors

  13. Defining A Schema (IE5) • Take an example XML document instance <?xml version="1.0"?> <pizzaOrder> <when>18:04:30</when> <cost>8.75</cost> <pizza>Hot n Spicy</pizza> </pizzaOrder>

  14. Defining A Schema (IE5) • First declare that it uses a schema definition via the default namespace <?xml version="1.0"?xmlns="x-schema:pizzaOrderSchema.xml"> <pizzaOrder> <when>18:04:30</when> <cost>8.75</cost> <pizza>Hot n Spicy</pizza> </pizzaOrder>

  15. Defining a Schema (IE5) • Now create an outline schema <Schemaxmlns="urn:schemas-microsoft-com:xml-data"> ... </Schema> • ie an XML document from the schema language namespace

  16. Defining a Schema (IE5) • First we declare the kinds of elements we have <Schema xmlns="urn:schemas-microsoft-com:xml-data"> <ElementType name="when"/> <ElementType name="cost"/> <ElementType name="pizza"/> <ElementType name="pizzaOrder"/> </Schema>

  17. Defining a Schema (IE5) • and specify allowable content <Schema xmlns="urn:schemas-microsoft-com:xml-data"> <ElementType name="when" content="textOnly"/> <ElementType name="cost" content="textOnly"/> <ElementType name="pizza" content="textOnly"/> <ElementType name="pizzaOrder" content="eltOnly"/> </Schema> • textOnly, eltOnly, mixed, empty

  18. Defining a Schema (IE5) • and then content model <Schema xmlns="urn:schemas-microsoft-com:xml-data"> <ElementType name="when" content="textOnly"/> <ElementType name="cost" content="textOnly"/> <ElementType name="pizza" content="textOnly"/> <ElementType name="pizzaOrder" content="eltOnly"> <element type="when"/> <element type="cost"/> <element type="pizza"/> </ElementType> </Schema>

  19. Defining a Schema (IE5) • and even the content model for text <Schema xmlns="urn:schemas-microsoft-com:xml-data"> <ElementType name="when" content="textOnly" type="time"/> <ElementType name="cost" content="textOnly" type="float"/> <ElementType name="pizza" content="textOnly"/> <ElementType name="pizzaOrder" content="eltOnly"> <element type="when"/> <element type="cost"/> <element type="pizza"/> ...

  20. Defining a Schema (IE5) • But that requires another namespace <Schema xmlns="urn:schemas-microsoft-com:xml-data"xmlns:dt="urn:schemas-microsoft-com:datatypes"> <ElementType name="when" content="textOnly" dt:type="time"/> <ElementType name="cost" content="textOnly" dt:type="float"/> <ElementType name="pizza" content="textOnly"/> <ElementType name="pizzaOrder" content="eltOnly"> <element type="when"/> <element type="cost"/> ...

  21. Schema Components • Schemas build on the declarations and usage of elements and attributes • ElementType elements declare a kind of element • AttributeType elements declare a kind of attribute • element elements show the use of an element within the context of another element • attribute elements show the use of an attribute on an element

  22. Schema Components • Various attributes specify the allowable properties each element or attribute • model specifies whether the element may contain 'foreign' elements, not specified in the schema • minOccurs and maxOccurs put lower- and upper-bounds on the repetition of an element • order specifies whether subelements must appear in the order specified, or whether only a single subelement can be chosen • required states that an attribute must be present • default gives a default value for a missing attribute

  23. Schema Data Types • Microsoft's Schema provides 23 built-in data types to which textual content can conform • various numeric types (float, ints) • date, time, urn, uuid, char, hex, boolean and blob • No derived / extended types are allowed • Separate namespace labels data vocab

  24. Using Data Types • A node's validated data type is directly accessible within the IE DOM • DOMelement.nodeTypedValue • instead of .nodeValue or .text • A node's schema definition is available • DOMElement.definition property seeweather.html

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