The Request Definitions segment of the WSDL defines Product Advertising API operation requests, as shown in the following WSDL snippet.

<xs:complexType name="ItemSearchRequest">
  <xs:sequence>
  <xs:element name="Actor" type="xs:string" minOccurs="0" /> 
  <xs:element name="Artist" type="xs:string" minOccurs="0" /> 
  <xs:element name="Availability" minOccurs="0">
    <xs:simpleType>
      <xs:restriction base="xs:string">
        <xs:enumeration value="Available" /> 
      </xs:restriction>
    </xs:simpleType>
  </xs:element>
  <xs:element ref="tns:AudienceRating" minOccurs="0" maxOccurs="unbounded" /> 

This snippet shows some of ItemSearch 's input parameters, including Actor, Artist, Availability, and AudienceRating. The element declarations specify that these parameters are valid in an ItemSearch request. Most of the parameters in this example are strings. The type of one, however, Availability, is a variation on the base class, string. In this case, the variation puts a restriction on the strings that can be valid values for Availability. For that reason, the restriction keyword is used. The restriction is that the valid values for Availability are defined by an enumeration. The enumeration, however, has only one valid value, "Available," which means that the parameter, Availability can be set to only one value.

minOccurs refers to the minimum number of times the parameter must appear in an ItemSearch request. If the value is zero, the associated parameter is optional. If the value is 1, the associated parameter is required to be included once in every request involving that operation. The default value is 1, that is, if minOccurs is not included in an element declaration, minOccurs is 1.

maxOccurs defines the maximum number of times the parameter can appear in a request. The default is 1, that is, if maxOccurs is not included in an element declaration, maxOccurs is 1 and the parameter can only appear once in a request. In the preceding example, maxOccurs is "unbounded," which means that the AudienceRating parameter can appear any number of times in an ItemSearch request.

In the preceding example, the parameter types are declared to be simpleTypes. A simple type cannot have child elements or attributes. Complex types can. In practice, any parameter that can take multiple values, such as an array, must be defined as a complex type.

The following snippet shows an example of a complex type.

<xs:element name="ItemSearch">
  <xs:complexType>
  <xs:sequence>
    <xs:element name="MarketplaceDomain" type="xs:string" minOccurs="0" /> 
    <xs:element name="AWSAccessKeyId" type="xs:string" minOccurs="0" /> 
    <xs:element name="SubscriptionId" type="xs:string" minOccurs="0" /> 

This definition snippet shows three of the parameters that can be part of an ItemSearch request.