what is service metadata and why it's necessary to publish?

Question

There is ABC (addres, binding, contract) = endpoint. I thought this information is enough to communicate with clients and vice versa. But what is metadata and mex?

Answer 1

The metadata that the mex endpoint exposes describes the service, the various operations, parameters the opertions require and the return types. In other words, the metadata exposes the contract. With this information the client can create a proxy to interact with the service. Clients use the mex endpoint to access the metadata.