(7) Removing Choices

• Complex types usually allow variability
  • minOccurs and maxOccurs allow variability in occurrences
  • choice groups allow to choose between a number of alternatives
  • attributes may be flagged as use="optional"
  • simple types allow the individual values to use certain sets of values
• Complex type restriction allows restrictions of all these variations
  • minOccurs and maxOccurs can be made more restrictive
  • alternatives can be removed from choice groups
  • optional attributes can flagged as use="required" or use="prohibited"
  • the simple types of values can be set to more restricted simple types
• The technical way of defining restrictions is cumbersome
  • when the base type changes, the restricted type has to be fixed by hand

(8) Complex Type Restriction (Example)

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 <xs:complexType name="addressType">
  <xs:sequence>
   <xs:element name="name" type="xs:string"/>
   <xs:element name="street" type="xs:string"/>
   <xs:element name="city" type="xs:string" minOccurs="0"/>
   <xs:choice>
    <xs:element name="state" type="xs:string"/>
    <xs:element name="canton" type="xs:string"/>
   </xs:choice>
   <xs:element name="zip" type="xs:decimal"/>
  </xs:sequence>
  <xs:attribute name="country" type="xs:NMTOKEN"/>
  <xs:attribute name="territory" type="xs:string" use="optional"/>
 </xs:complexType>
 <xs:complexType name="USaddressType">
  <xs:complexContent>
   <xs:restriction base="addressType">
    <xs:sequence>
     <xs:element name="name" type="xs:string"/>
     <xs:element name="street" type="xs:string"/>
     <xs:element name="city" type="xs:string"/>
     <xs:choice>
      <xs:element name="state" type="xs:string"/>
     </xs:choice>
     <xs:element name="zip" type="zipType"/>
    </xs:sequence>
    <xs:attribute name="country" type="xs:NMTOKEN"/>
    <xs:attribute name="territory" type="xs:string" use="prohibited"/>
   </xs:restriction>
  </xs:complexContent>
 </xs:complexType>
 <xs:simpleType name="zipType">
  <xs:restriction base="xs:decimal">
   <xs:totalDigits value="5"/>
  </xs:restriction>
 </xs:simpleType>
</xs:schema>

(9) Processing Restricted Complex Types

• Values of restricted types are values of the base types
  • type restriction is defined so that restricted type values are always base type values
  • code processing a type can be reused to process restricted types
• If there is a well-designed type hierarchy, programming becomes easier
  • simple code can be written to handle the basic types
  • if required, more advanced code can be written for the restricted types
  • in many cases, restriction is more for validation than for processing
• XSDs may even use abstract types
  • no element will ever use the addressType
  • concrete elements will only use restricted types
  • there can be code handling the addressType which handles all addresses

(11) Adding Content

• Complex types are element content and attributes
  • extensions can add content, but only at the end of the base content
  • extensions can add attributes (order is not significant for attributes)
• Adding content to existing content may not change the existing content
  • if the content is element only, it has to remain element only
  • if the content is mixed, is has to remain mixed
  • if the content is empty, it may become element only or mixed
  • the reason for these rules is that mixed is a global property of a type
• Adding attributes simply adds these to the list of existing attributes
  • the added attributes may be optional or required

(12) Complex Type Extension (Example)

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 <xs:complexType name="addressType">
  <xs:sequence>
   <xs:element name="name" type="xs:string"/>
   <xs:element name="street" type="xs:string"/>
   <xs:element name="city" type="xs:string" minOccurs="0"/>
   <xs:choice>
    <xs:element name="state" type="xs:string"/>
    <xs:element name="canton" type="xs:string"/>
   </xs:choice>
   <xs:element name="zip" type="xs:decimal"/>
  </xs:sequence>
  <xs:attribute name="country" type="xs:NMTOKEN"/>
  <xs:attribute name="territory" type="xs:string" use="optional"/>
 </xs:complexType>
 <xs:complexType name="businessAddressType">
  <xs:complexContent>
   <xs:extension base="addressType">
    <xs:sequence>
     <xs:element name="company" type="xs:string"/>
     <xs:element name="position" type="xs:string" minOccurs="0"/>
    </xs:sequence>
    <xs:attribute name="relationship" type="xs:NMTOKEN"/>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>
</xs:schema>

(13) Processing Extended Complex Types

• Values of extended types are not values of the base types
  • type extension adds content add/or attributes to a type
  • if content is added, it is always added at the end of the base type's content
• If there is a well-designed type hierarchy, programming becomes easier
  • simple code can be written to handle the basic types
  • if that should handle extended types, it must be written to handle extensions
  • handling extensions can be as simple as skipping them
• XSDs may even use abstract types
  • no element will ever use the addressType
  • concrete elements will only use extended types
  • code handling extended types can build on code handling the base type