How do you retrieve data from a WCF Web Service effectively?

Retrieving data from a WCF (Windows Communication Foundation) Web Service effectively typically involves creating an instance of the web service client class. This is because WCF services are often designed with service contracts, and generating a service client class allows you to communicate with the service in a type-safe manner.

When you create an instance of the web service client, you can call the methods defined in the service contract directly, taking advantage of the strongly-typed nature of the client. This method simplifies interaction by automatically handling the serialization and deserialization of data, making it easier to work with complex data types defined in the service.

The other options involve methods that either do not directly relate to WCF, like using a REST API call, which instead pertains to RESTful services, or issuing a direct SQL command, which bypasses the service abstraction entirely. Using a SOAP envelope is more about the protocol used in the communication rather than the effective retrieval of data in the context of WCF service clients. Thus, creating an instance of the web service client class is the most effective and appropriate means of retrieving data from a WCF Web Service.