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XML Validation II Schemas

XML Validation II Schemas. Robin Burke ECT 360. Outline. Namespaces Documents  Data types XML Schemas Elements Attributes Derived data types RELAX NG. XML so far. Languages defined by DTDs names assigned by designers OK for standalone systems Doesn't have

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XML Validation II Schemas

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  1. XML Validation IISchemas Robin Burke ECT 360

  2. Outline • Namespaces • Documents  Data types • XML Schemas • Elements • Attributes • Derived data types • RELAX NG

  3. XML so far • Languages defined by DTDs • names assigned by designers • OK for standalone systems • Doesn't have • The ability to handle naming conflicts • The ability to partition work among different developers

  4. Namespaces • A way to identify a set of labels • element / attribute names • attribute values • As belonging to a particular application

  5. Example • recordings • title • artist • group | artist-name+ • date • label • artworks • title • artist • date • exhibit • books • title • author • date • publisher

  6. Problem • Want to create a list of items related to 50s Beat-era culture • includes music, art, literature • Could create a new DTD • better to reuse existing ones

  7. Namespace idea • Associate a short prefix with an application • Schema or DTD • Use the prefix with a colon to "qualify" names • music:artist • art:artist • book:author

  8. Namespace idea, cont'd • A namespace is an association between • a set of names • a unique identifier (URI) • a prefix used to identify them

  9. Namespace declaration • Standalone <?xml:namespace ns="http://bookpeople.com/book" prefix="book"?> • Part of element <html xmlns="http://www.w3.org/1999/xhtml"> • in this case, no prefix <book xmlns:book="http://bookpeople.com/book">

  10. Namespace URI • Not a URL • there is no resource at the given location • just a unique identifier • URL-like identifiers are good • associated with an organization • must be unique on the Internet

  11. Example • DTDs • Document • Problem • how to import the namespaces?

  12. Solution • Fully-qualified names everywhere • yuk! • DTDs & namespaces don't work well together

  13. XML so far • Languages defined by DTDs • contain text elements • string attributes • OK for text documents • Not enough for • Databases • Business process integration

  14. Other DTD problems • Not XML • different syntax • different processor • No support for namespaces

  15. Solution • Write language definition in XML • Allow more control over document contents • XML document becomes • a complex data type • XML language definition becomes • complex data type specification

  16. XML Schema • Always a separate document • no internal option • Written in XML • very verbose • Can be complex

  17. Schemas and namespaces • A schema • uses elements from one application • the XML Schema language • to define another • Namespaces are necessary • Namespaces apply to elements • not values • Namespace of element assumed to apply to attributes • can have attributes from different namespaces <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">

  18. Example 1, XML <grades assignment="Homework 1"> <grade> <student id="1234-12345">Jane Doe</student> <assigned-grade>A</assigned-grade> </grade> <grade> <student id="5432-54321">John Doe</student> <assigned-grade>B</assigned-grade> </grade> </grades>

  19. Example 1, DTD <!ELEMENT grades (grade*)> <!ATTLIST grades assignment CDATA #IMPLIED> <!ELEMENT grade (student, assigned-grade)> <!ELEMENT student (#PCDATA)> <!ATTLIST student id CDATA #REQUIRED> <!ELEMENT assigned-grade (#PCDATA)>

  20. Data types • grades • a collection of items of type grade • can never have more than 40 students • grade • a structure containing a student and an assigned grade • student • a structure containing an id and some text • probably should constrain the student id • assigned-grade is text • probably should constrain to A-D,F,I

  21. Built-in types • Part of the schema language • Base types • 19 fundamental types • Examples: string, decimal • Derived types • 25 more types that use the base types • Examples: ID, positiveInteger

  22. Built-in types, cont'd

  23. To declare an element <xs:element name="assigned-grade" type="string"> • Equivalent to <!ELEMENT assigned-grade (#PCDATA)>

  24. Simple data type • A renaming of an existing data type <xs:element name="assigned-grade" type="xs:string"> • Or a restriction of a existing type • strings beginning with "D" • more on this later

  25. Complex datatype <xs:element name=“name”> <xs:complexType> compositor element declarations attribute declarations </xs:complexType> </xs:element>

  26. Compositor • sequence • choice • all

  27. Sequence compositor • like "," in DTD • DTD <!ELEMENT foo (bar, baz)> • Schema <xs:element name="foo"> <xs:complexType> <xs:sequence> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:sequence> </xs:complexType> </xs:element>

  28. Elements in sequences • Can specify optional / # of occurrences • ? <xs:element ref="bar" minOccurs="0" type="xs:string"> • * <xs:element ref="bar" minOccurs="0" maxOccurs="unbounded" /> • + <xs:element ref="bar" minOccurs="1" maxOccurs="unbounded" /> • What about... <xs:element ref="bar" minOccurs="2" maxOccurs="4" />

  29. Choice compositor • like "|" in DTD • DTD <!ELEMENT foo (bar | baz)> • Schema <xs:element name="foo"> <xs:complexType> <xs:choice> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:choice> </xs:complexType> </xs:element>

  30. All compositor • no simple DTD equivalent • DTD <!ELEMENT foo ( (bar, baz?) | (baz, bar?) > • Schema <xs:element name="foo"> <xs:complexType> <xs:all> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:all> </xs:complexType> </xs:element>

  31. Nesting • Compositors can be combined • DTD <!ELEMENT foo ( (bar, baz) | (thud, grunt) )> • Schema <xs:element name="foo"> <xs:complexType> <xs:sequence> <xs:choice> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:choice> <xs:choice> <xs:element ref="thud" /> <xs:element ref="grunt" /> </xs:choice> </xs:sequence> </xs:complexType> </xs:element>

  32. Example <!ELEMENT grades (grade*)> <!ELEMENT grade (student, assigned-grade)> <!ELEMENT student (#PCDATA)> <!ELEMENT assigned-grade (#PCDATA)>

  33. Local naming • Suppose we want to reuse an element name • different place in the structure • Example • <!ELEMENT url-catalog (link*)> • <!ELEMENT link (link, description?)> • not a legal DTD • schema?

  34. Using namespaces • Schema must say • to use schema namespace • what namespace it is defining • targetNamespace • Document must say • that it is using the Schema Instance namespace • what namespace(s) it is using • what prefix(es) are used • where to find the relevant schemas

  35. Multi-schema documents • Possible to validate multi-schema documents • Must use any element to import namespace • can't restrict to certain elements

  36. Attributes • DTD attribute types • CDATA, enumeration, token • Schema • can be any of the basic or derived types • can also be user-defined types • Declaration <xs:attribute name="x" type="xs:string" use="required" default="abc" />

  37. Attribute declaration • Part of complex type • follows compositor • (one exception) • Declaration <xs:attribute name="foo" type="xs:positiveInteger" /> • What if the attribute is a more complex type itself? • we'll get to that

  38. Example • grades element? • add homework attribute

  39. Exception: simple content • If an element has "simple content" • no compositor used • instead simpleContent element • and extension to declare type of the content

  40. Example <!ELEMENT student (#PCDATA)> <!ATTLIST student id CDATA #REQUIRED > <xs:element name="student"> <xs:complexType> <xs:simpleContent> <xs:extension base="xs:string"> <xs:attribute name="id" type="xs:string" use="required"/> </xs:extension> </xs:simpleContent> </xs:complexType> </xs:element>

  41. How to read this • student is a complex type • it is not simply a renaming of an existing type • its content is simple • being of only one type • string • but with an attribute • id of type string which is required

  42. Standalone types • A type can stand outside of an element definition • must have a name <xs:complexType name="bar-n-baz"> <xs:sequence> <xs:element ref="bar" /> <xs:element ref="baz" /> </xs:sequence> </xs:complexType> • Used in element definition <xs:element name="foo" type="bar-n-baz" />

  43. Deriving types • DTDs do not allow types restrictions • beyond enumeration, CDATA, token • for attributes • PCDATA • for content • Schemas have built-in types • also capability to create your own

  44. Derivation operations • list • sequence of values • union • combine two types • allowing either • restriction • placing limits on the legal values

  45. List <xs:element name="partList"> <xs:simpleType> <xs:list itemType="partNo" /> </xs:simpleType> </xs:element> <partList>PN334-04 PN223-89 PQ1112-03</partList> • Must be separated by spaces • probably more useful to do this with document structure • partList -> partNo*

  46. Union • Allows data of either type to be used • Example <xs:simpleType name="xs:integer"> <xs:union memberTypes="xs:negativeInteger xs:nonNegativeInteger" /> </xs:simpleType> • Bogus!

  47. Restriction • Most useful • Allow design to state exactly what values are legal • prices must be non-negative • SSN must follow a certain pattern • in-stock must yes or no • etc.

  48. Restriction, cont'd • Restrict a base type • according to "facets" • Different facets available for different data types

  49. Facets

  50. Example: enumeration <xs:simpleType name="grade"> <xs:restriction base="xs:string"> <xs:enumeration value="A"/> <xs:enumeration value="B"/> <xs:enumeration value="C"/> <xs:enumeration value="D"/> <xs:enumeration value="F"/> <xs:enumeration value="I"/> </xs:restriction> </xs:simpleType>

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