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2.5 XML Schemas

2.5 XML Schemas. A quick introduction to XML Schema W3C Recommendation, May 2, 2001: XML Schema Part 0: Primer (readable non-normative introduction; Recommended) XML Schema Part 1: Structures XML Schema Part 2: Datatypes Also under development:

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2.5 XML Schemas

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  1. 2.5 XML Schemas • A quick introduction to XML Schema • W3C Recommendation, May 2, 2001: • XML Schema Part 0: Primer (readable non-normative introduction; Recommended) • XML Schema Part 1: Structures • XML Schema Part 2: Datatypes • Also under development: • XML Schema: Formal Description, W3C Working Draft, 25 September 2001 Notes 2: Document Instances and Grammars

  2. Schema terminology • Schema: a formal description for the structure and allowed content of a set of data (esp. in databases) • “XML Schema” is often used for each of … 1.XML Schema, the W3C Rec. that defines … 2.XML Schema Definition Language (XSDL), an XML-based markup language for expressing ... 3.schema documents, each of which describes a schema ( DTD) for a set of XML document instances (This may cause some confusion!) Notes 2: Document Instances and Grammars

  3. Advantages of XSDL (1) • XML syntax • schema documents easier to manipulate by programs (than the special DTD syntax) • Compatibility with namespaces • can validate documents using declarations from multiple sources • Content datatypes • 44 built-in datatypes (including primitive Java datatypes, datatypes of SQL, and XML attribute types) • mechanisms to derive user-defined datatypes Notes 2: Document Instances and Grammars

  4. XSDL built-in types (Part 2, Chap. 3) Notes 2: Document Instances and Grammars

  5. Advantages of XSDL (2) • Independence of element names and content types; Compare with • DTDs: 1-to-1 correspondence btw. element type names and their content models • CFGs: 1-to-1 correspondence btw. nonterminals and their productions • For example, could define titles of people as “Mr.”/”Mrs.”/”Ms.” and titles of chapters as strings Notes 2: Document Instances and Grammars

  6. Advantages of XSDL (3) • Support for schema documentation • element annotation with sub-elementsdocumentation (for human readers) andappInfo (for applications) • Ability to specify uniqueness and keys within selected parts of document • for example, that titlesof chapters should be unique Notes 2: Document Instances and Grammars

  7. Disadvantages of XSDL • Complexity of XSDL (esp. of Rec. Part 1!) • > a long learning curve • Possible immaturity of implementations (?) • W3C XML Schema Web site mentions a dozen of tools or processors (http://www.w3.org/XML/Schema#Tools, March 2002) • Open-source Apache XML parsers (Xerces C++ 1.7.0 and Xerces Java 1.4.4) seem reasonable implementations, but also document limitations/problems in their XML Schema support Notes 2: Document Instances and Grammars

  8. XSDL through Example • Next: walk-through of an XML schema example • from XML Schema Rec, Part 0, Chap. 2 • Modelling purchase orders like below:<purchaseOrder orderDate="1999-10-20"> <shipTo country="US"> <name>Alice Smith</name> <street>123 Maple Street</street> <city>Mill Valley</city> <state>CA</state> <zip>90952</zip> </shipTo> Notes 2: Document Instances and Grammars

  9. purchaseOrder instance continues <billTo country="US"> <name>Robert Smith</name> <street>8 Oak Avenue</street> <city>Old Town</city> <state>PA</state> <zip>95819</zip> </billTo> <comment>Hurry, my lawn is wild!</comment> <items><item partNum="872-AA"> <productName>Lawnmower</productName> <quantity>1</quantity> <USPrice>148.95</USPrice> <comment>Only if electric</comment> </item> Notes 2: Document Instances and Grammars

  10. End of the example instance <item partNum="926-AA"> <productName>Baby Phone</productName> <quantity>1</quantity> <USPrice>39.98</USPrice> <shipDate>1999-05-21</shipDate> </item> </items> </purchaseOrder> • Next: A schema for this kind of purchase orders Notes 2: Document Instances and Grammars

  11. The Purchase Order Schema (1/5) <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="purchaseOrder” type="POrdType"/> <xs:element name="comment" type="xs:string"/> <xs:complexType name="POrdType"> <xs:sequence> <xs:element name="shipTo” type="USAddr"/> <xs:element name="billTo" type="USAddr"/> <xs:element ref="comment" minOccurs="0"/> <xs:element name="items" type="Items"/> </xs:sequence> <xs:attribute name="ordDate” type="xs:date"/> </xs:complexType> Notes 2: Document Instances and Grammars

  12. The Purchase Order Schema (2/5) <xs:complexType name="USAddr"> <xs:sequence> <xs:element name="name" type="xs:string"/> <xs:element name="street" type="xs:string"/> <xs:element name="city" type="xs:string"/> <xs:element name="state" type="xs:string"/> <xs:element name="zip" type="xs:decimal"/> </xs:sequence> <xs:attribute name="country" type="xs:NMTOKEN" fixed="US"/> </xs:complexType> Notes 2: Document Instances and Grammars

  13. The Purchase Order Schema (3/5) <xs:complexType name="Items"> <xs:sequence> <xs:element name="item" minOccurs="0" maxOccurs="unbounded"> <xs:complexType> <xs:sequence> <xs:element name="productName" type="xs:string"/> <xs:element name="quantity"> <xs:simpleType> <xs:restriction base="xs:positiveInteger"> <xs:maxExclusive value="100"/> </xs:restriction> </xs:simpleType> </xs:element> anonymous type for item anon. type for quantity Notes 2: Document Instances and Grammars

  14. The Purchase Order Schema (4/5) <xs:element name="USPrice" type="xs:decimal"/> <xs:element ref="comment" minOccurs="0"/> <xs:element name="shipDate" type="xs:date" minOccurs="0"/> </xs:sequence> <xs:attribute name="partNum" type="SKU" use="required"/> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> Notes 2: Document Instances and Grammars

  15. The Purchase Order Schema (5/5) <!-- Type for Stock Keeping Units, (codes for identifying products): --> <xs:simpleType name="SKU"> <xs:restriction base="xs:string"> <xs:pattern value="\d{3}-[A-Z]{2}" /> </xs:restriction> </xs:simpleType> </xs:schema> Notes 2: Document Instances and Grammars

  16. XSDL Content Models • Element content of complexType can be regulated using • group elements sequence, choice and all and • occurrence constraint attributes minOccurs and maxOccurs • Elements sequence and choice correspond to catenation and alternativity ( | ) in regular expressions Notes 2: Document Instances and Grammars

  17. default of both is 1 XSDL occurrence constraints • optionality (E?) can be expressed by minOccurs=’0’ • iteration (E*) can be expressed by minOccurs=’0’and maxOccurs=’unbounded’ • Exactly five occurrences of element A:<xs:element name=”A” minOccurs=’5’ maxOccurs=’5’ /> • 10 to 900 occurrences of element A:<xs:element name=”A” minOccurs=’10’ maxOccurs=’900’ /> Notes 2: Document Instances and Grammars

  18. Regular expression vs an XSDL content model • A+ | B (C D)* could be expressed by <xs:choice> <xs:element name=”A” type=”typeA” maxOccurs=’unbounded’ /> <xs:sequence> <xs:element name=”B” type=”typeB” /> <xs:sequence minOccurs=’0’ maxOccurs=’unbounded’ > <xs:element name=”C” type=”typeC” /> <xs:element name=”D” type=”typeD” /> </xs:sequence> </xs:sequence> </xs:choice> Notes 2: Document Instances and Grammars

  19. The all group • XSDL all group is a restricted version of the SGML &-connector • E1 & … & En allows sequences corresponding to any permutation of E1, …, En • XSDL all restricted to appear as the only content model group of a complexType, and its children to (possibly optional) element Notes 2: Document Instances and Grammars

  20. The all group: An example • For example <xs:all> <xs:element name=”A” /> <xs:element name=”B” /> <xs:element name=”C” minOccurs=’0’ /></xs:all>accepts all of the following element sequences: A B C; A C B; B A C; B C A; C A B; C B A; A B; and B A; Notes 2: Document Instances and Grammars

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