WSDL - Message Exchange Patterns (MEP)

What is MEP?

Message Exchange Pattern (MEP) in WSDL defines how messages flow between a client (service consumer) and a web service (service provider).
It specifies the sequence and direction of messages for each operation in a portType.

In simple terms:

• PortType + Operations = What service can do

• MEP = How messages are exchanged for those operations

Types of Message Exchange Patterns in WSDL

1. One-Way

• Description: The client sends a request message, but the service does not send back a response.

• Example: Logging service where the client sends log data.

• Flow: Client → Service

<operation name="SubmitLog">
  <input message="tns:LogMessage"/>
</operation>

2. Request-Response

• Description: The most common MEP. The client sends a request message, and the service responds with a reply.

• Example: Weather service where the client sends a city name and gets the forecast.

• Flow: Client → Service → Client

<operation name="GetWeather">
  <input message="tns:GetWeatherRequest"/>
  <output message="tns:GetWeatherResponse"/>
</operation>

3. Solicit-Response

• Description: The service initiates communication by sending a request, and the client replies.

• Example: A stock trading service might solicit updated portfolio data from the client.

• Flow: Service → Client → Service

<operation name="SolicitPortfolioUpdate">
  <output message="tns:PortfolioRequest"/>
  <input message="tns:PortfolioResponse"/>
</operation>

4. Notification

• Description: The service sends a message to the client, but no response is expected.

• Example: A news service pushing breaking news alerts.

• Flow: Service → Client

<operation name="BreakingNews">
  <output message="tns:NewsMessage"/>
</operation>

Summary Table: WSDL MEPs