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XML Schemas continued..

Attributes

Attributes are always of SimpleType (since tehy don't contain otherelements or attributes)

Attributes always appear in ComplexType elements

Declared in an XML Schema like:

  • <xs:attribute name="coverType" type="xs:string" use="required"/>

Attributes default to OPTIONAL if you don't specify use="required"

Pre-define an attribute's value using value="blah"

Occurence Constructs

Define the number of times an element can occur - correlates to + or * or ? in DTDs

maxOccurs - specifies the maximum number of times an element can occur

  • can be 1 to 'unbounded' (no limit)

minOccurs - specifies teh minimum number of tiems an element can occur

  • can be 0 (optional) or some other integer

Custom Simple Types

Allow a developer to define their own rules for a type declaration - zip code or phone number are great examples


<xs:simpleType name="phoneNumberType">
  <xs:restriction base="xs:string">
    <xs:pattern value="\d{3}-\d{3}-\d{4}"/>
  </xs:restriction>
</xs:simpleType>

Patterns - RegEx

Used to match patterns in strings

XML uses Perl's regular expression dialect. For more details see: https://perldoc.perl.org/perlre.html#Regular-Expressions

Range Constructs

Range constructs limit the range of simple tyoes that are numerically and date based

  • maxInclusive - used to set an upper limit that INCLUDES the value that it is set to
  • maxExclusive - used to set an upper limit that EXCLUDES the value that it is set to
  • minInclusive - used to set an lower limit that INCLUDES the value that it is set to
  • minExclusive - used to set an lower limit that EXCLUDES the value that it is set to

Annotations

Annotations are simply a special type of comment that software programs can read

Used for documenting web services and other public APIs

Declared like:


<xs:annotation>
  <xs:documentation>blah, blah, blah...</xs:documentation>
</xs:annotation>

Scope

Local scope is simply defined as having everything nested

Global scope allows the developer to 'name' a complexType or simpleType so that the type can be reused in the XSD

Global scope element types should be direct child elements of <xs:schema>

Define a global scope for an element by:


<xs:schema>

  // 1. Giving it a name
  <xs:element name="address" type="addressType"/>

  // 2. Creating a definition as a child under <xs:schema>
  <xs:complexType name="addressType">
    <xs:sequence>
      ...
    </xs:sequence>    
</xs:schema>