https://www.w3.org/2004/07/xml2004-hh/wsdl20-update.html
Message exchange patterns
WSDL 2.0 describe a service from the point of view of the service itself. Messages are going in (input messages) and out (output messages). The sequence and cardinality of abstract messages listed in an operation is called a message exchange pattern (MEP). Unlike WSDL 1.1, [WSDL Version 2.0: Predefined Extensions] carefully describe the sequence, direction (in or out) and cardinality of the messages that are involved in the exchange, as well as identifying the parties involved. The eight following MEPs are defined in [WSDL Version 2.0: Predefined Extensions]:
In-Only. This pattern consists of exactly one message received by a service from some other node. No fault may be generated.
Robust In-Only. This pattern can be considered as a variation of In-Only. It also consists of exactly one message received by a service, but in this case faults can be triggered by the message received.
In-Out. This pattern consists of exactly two messages: a message received by a service from some other node, followed by a message sent to the other node. The second message may be replaced by a fault.
In-Optional-Out. This patten consists of one or two messages: a message received by a service from some other node, optionally followed by a message sent to the other node from the service. Each message may trigger a fault in response.
Out-Only. This pattern consists of exactly one message sent to some other node from a service. No fault maybe generated.
Robust Out-Only. This pattern can be considered as a variation of Out-only. It also consists of exactly one message sent to some other node from a service, but in this case faults can be triggered by the message.
Out-in. This pattern consists of exactly two messages: a message sent to some other node from a service, followed by a message received by the service from the other node. The second message may be replaced by a fault.
Out-Optional-In. This pattern consists of one or two messages: a message sent to some other node from a service, optionally followed by a message received by the service from the other node. Each message may trigger a fault in response.
Other MEPs may be defined and used by an interface operation.
Pessoal, no WSDL 1.1 tinhamos 4 tipos básicos de operação: Unidirecional, Request-Response, Solicit Response e Notification. A partir do WSDL 2 essas definições mudaram:
Apenas-Entrada (In-Only): É equivalente ao unidirecional. Um padrão de troca de mensagem unidirecional onde o consumidor envia uma mensagem ao provedor que fornece apenas uma resposta de estado.
Apenas-Entrada Robusto (Robust In-Only): Este padrão é para a troca de mensagens confiável unidirecional. O consumidor inicia com uma mensagem a qual o provedor respondo com o estado. Se a resposta for um estado, a troca está completa, mas se for uma falha, o consumidor deve responder com um estado.
Entrada-Saída (In-Out): É equivalente à solicitação-resposta. Um padrão de troca de mensagens bidirecional onde o consumidor inicia com uma mensagem, o provedor responde com uma mensagem ou uma falha e o consumidor responde com um estado.
Entrada e Saída-Opcional (In Optional-Out): Um padrão de troca de mensagens bidirecional onde a resposta do provedor é opcional.
Apenas Saída
Apenas Saída Robusto
Saída Entrada
Saída Entrada-Opcional