Is WSDL binding optional?

Question

I have a wsdl file without binding section:

<?xml version="1.0" encoding="utf-8" standalone="no"?>
<wsdl:definitions xmlns:msc="http://schemas.microsoft.com/ws/2005/12/wsdl/contract" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:soap12="http://schemas.xmlsoap.org/wsdl/soap12/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:tns="http://tempuri.org/" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:wsa10="http://www.w3.org/2005/08/addressing" xmlns:wsam="http://www.w3.org/2007/05/addressing/metadata" xmlns:wsap="http://schemas.xmlsoap.org/ws/2004/08/addressing/policy" xmlns:wsaw="http://www.w3.org/2006/05/addressing/wsdl" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns:wsp="http://schemas.xmlsoap.org/ws/2004/09/policy" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:wsx="http://schemas.xmlsoap.org/ws/2004/09/mex" xmlns:xsd="http://www.w3.org/2001/XMLSchema" name="Engage" targetNamespace="http://tempuri.org/" xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/" xmlns:http="http://schemas.xmlsoap.org/wsdl/http/">
  <wsdl:types>
    <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" targetNamespace="http://tempuri.org/">
      <xs:element name="OtherData">
        <xs:complexType>
          <xs:sequence>
            <xs:element minOccurs="0" name="id" nillable="true" type="xs:string" />
          </xs:sequence>
        </xs:complexType>
      </xs:element>
      <xs:element name="OtherDataResponse">
        <xs:complexType>
          <xs:sequence>
            <xs:element minOccurs="0" name="OtherDataResult" nillable="true" type="xs:string" />
          </xs:sequence>
        </xs:complexType>
      </xs:element>
      <xs:element name="MyData">
        <xs:complexType>
          <xs:sequence>
            <xs:element minOccurs="0" name="id" nillable="true" type="xs:string" />
          </xs:sequence>
        </xs:complexType>
      </xs:element>
      <xs:element name="MyDataResponse">
        <xs:complexType>
          <xs:sequence>
            <xs:element minOccurs="0" name="MyDataResult" nillable="true" type="xs:string" />
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:schema>
    <xs:schema xmlns:tns="http://schemas.microsoft.com/2003/10/Serialization/" xmlns:xs="http://www.w3.org/2001/XMLSchema" attributeFormDefault="qualified" elementFormDefault="qualified" targetNamespace="http://schemas.microsoft.com/2003/10/Serialization/">
      <xs:element name="anyType" nillable="true" type="xs:anyType" />
      <xs:element name="anyURI" nillable="true" type="xs:anyURI" />
      <xs:element name="base64Binary" nillable="true" type="xs:base64Binary" />
      <xs:element name="boolean" nillable="true" type="xs:boolean" />
      <xs:element name="byte" nillable="true" type="xs:byte" />
      <xs:element name="dateTime" nillable="true" type="xs:dateTime" />
      <xs:element name="decimal" nillable="true" type="xs:decimal" />
      <xs:element name="double" nillable="true" type="xs:double" />
      <xs:element name="float" nillable="true" type="xs:float" />
      <xs:element name="int" nillable="true" type="xs:int" />
      <xs:element name="long" nillable="true" type="xs:long" />
      <xs:element name="QName" nillable="true" type="xs:QName" />
      <xs:element name="short" nillable="true" type="xs:short" />
      <xs:element name="string" nillable="true" type="xs:string" />
      <xs:element name="unsignedByte" nillable="true" type="xs:unsignedByte" />
      <xs:element name="unsignedInt" nillable="true" type="xs:unsignedInt" />
      <xs:element name="unsignedLong" nillable="true" type="xs:unsignedLong" />
      <xs:element name="unsignedShort" nillable="true" type="xs:unsignedShort" />
      <xs:element name="char" nillable="true" type="tns:char" />
      <xs:simpleType name="char">
        <xs:restriction base="xs:int" />
      </xs:simpleType>
      <xs:element name="duration" nillable="true" type="tns:duration" />
      <xs:simpleType name="duration">
        <xs:restriction base="xs:duration">
          <xs:pattern value="\-?P(\d*D)?(T(\d*H)?(\d*M)?(\d*(\.\d*)?S)?)?" />
          <xs:minInclusive value="-P10675199DT2H48M5.4775808S" />
          <xs:maxInclusive value="P10675199DT2H48M5.4775807S" />
        </xs:restriction>
      </xs:simpleType>
      <xs:element name="guid" nillable="true" type="tns:guid" />
      <xs:simpleType name="guid">
        <xs:restriction base="xs:string">
          <xs:pattern value="[\da-fA-F]{8}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{12}" />
        </xs:restriction>
      </xs:simpleType>
      <xs:attribute name="FactoryType" type="xs:QName" />
      <xs:attribute name="Id" type="xs:ID" />
      <xs:attribute name="Ref" type="xs:IDREF" />
    </xs:schema>
  </wsdl:types>
  <wsdl:message name="IMyService_OtherData_InputMessage">
    <wsdl:part element="tns:OtherData" name="parameters" />
  </wsdl:message>
  <wsdl:message name="IMyService_OtherData_OutputMessage">
    <wsdl:part element="tns:OtherDataResponse" name="parameters" />
  </wsdl:message>
  <wsdl:message name="IMyService_MyData_InputMessage">
    <wsdl:part element="tns:MyData" name="parameters" />
  </wsdl:message>
  <wsdl:message name="IMyService_MyData_OutputMessage">
    <wsdl:part element="tns:MyDataResponse" name="parameters" />
  </wsdl:message>
  <wsdl:portType name="IMyService">
    <wsdl:operation name="OtherData">
      <wsdl:input message="tns:IMyService_OtherData_InputMessage" wsaw:Action="http://tempuri.org/IMyService/OtherData" />
      <wsdl:output message="tns:IMyService_OtherData_OutputMessage" wsaw:Action="http://tempuri.org/IMyService/OtherDataResponse" />
    </wsdl:operation>
    <wsdl:operation name="MyData">
      <wsdl:input message="tns:IMyService_MyData_InputMessage" wsaw:Action="http://tempuri.org/IMyService/MyData" />
      <wsdl:output message="tns:IMyService_MyData_OutputMessage" wsaw:Action="http://tempuri.org/IMyService/MyDataResponse" />
    </wsdl:operation>
  </wsdl:portType>
  <wsdl:service name="MyService">
    <wsdl:port name="xmlPort">
      <http:address location="http://localhost:59109/MyService.svc/xml" />
    </wsdl:port>
    <wsdl:port name="jsonPort">
      <http:address location="http://localhost:59109/MyService.svc/json" />
    </wsdl:port>
  </wsdl:service>
</wsdl:definitions>

Is this wsdl valid? Or in other words can we have wsdl without a binding section or it is required and this wsdl is invalid? Some tools (like SoapUI) throws exception but the other (like this https://www.wsdl-analyzer.com/) says that this is valid wsdl.

Answer 1

According to the W3C note about WSDL 1.1:

There may be any number of bindings for a given portType

Does it mean there can be no bindings? Well, taking look at the XML schema for WSDL 1.1, binding element can have no occurences at all.

The practical behavior probably depends on a SOAP library. Note that the binding specifies whether we use document or RFC-style call and whether we encode the data or not.