Elements in XML

• Instance example
• Schema example
• Schema template
• Schema restrictions
  • Prohibited types
  • Prohibited attributes

Instance example

<nc:Person>
  <nc:PersonName structures:id="a123">
    <nc:PersonGivenName>John</nc:PersonGivenName>
    <nc:PersonMiddleName nc:personNameInitialIndicator="true">Q</nc:PersonMiddleName>
    <nc:PersonSurName>Smith</nc:PersonSurName>
  </nc:PersonName>
</nc:Person>

• nc:Person is an element that carries complex content.
• nc:PersonName is an element that carries complex content and an attribute.
• nc:PersonGivenName and nc:PersonSurName are elements that carry simple content (values).
• nc:PersonMiddleName is an element that carries simple content (a value) and an attribute.

Schema example

Despite the variations, each of the elements above is defined the same way in a schema. The different representations are defined by the element’s type, not by the element itself.

<!-- Element with complex content -->
<xs:element name="Person" type="nc:PersonType" nillable="true">
  <xs:annotation>
    <xs:documentation>A human being.</xs:documentation>
  </xs:annotation>
</xs:element>

<!-- Element with simple content -->
<xs:element name="PersonMiddleName" type="nc:PersonNameTextType" nillable="true">
  <xs:annotation>
    <xs:documentation>A middle name of a person.</xs:documentation>
  </xs:annotation>
</xs:element>

Schema template

<xs:element name="NAME" type="TYPE" nillable="true">
  <xs:annotation>
    <xs:documentation>DEFINITION</xs:documentation>
  </xs:annotation>
</xs:element>

Schema restrictions

The following is a list of restrictions that the NIEM NDR defines relating to XML element declarations.

Prohibited types

• xs:anySimpleType
• xs:anyType

These types are not allowed to prevent elements acting as wildcards. Substitutions and augmentations should be used instead.

Prohibited attributes

The following attributes may not be used in the declaration of an element in an XML Schema:

• block
• final
• default
• fixed

NIEM is designed to be extensible and customizable, in order to support a wide-ranging variety of requirements. The block and final attributes above prevent further customization by subsequent schemas.

The default and fixed attributes can result in unexpected behavior. A validating parser may construct values for an element assigned a default or fixed value in its schema; a non-validating parser will not. Preventing these attributes ensures that the information in an instance is not altered, depending on which parser is used to process the data.