Web Services for Coarse-Grained Business Logic
Both HTTP and XML are text-based formats and thus are more verbose than binary formats. The choices of technology and formats for web services were inherently not based on optimizing the exchange for performance or verboseness of the transfer. Other factors were more important: interoperability, wide-ranging support, using existing web technologies, leveraging infrastructure to go through firewalls, viewing the messages flowing through the wire easily with XML. As a consequence, the roundtrip delay in response while accessing a web service likely will be far higher compared to other distributed technologies. To keep the response time within acceptable limits, the expectation is that the service module would process a more coarse-grained functionality or even do composite tasks together to avoid multiple roundtrip delays. This plan makes web services better for exposing coarse-grained business functionality rather than a fine-grained operation.
This may be a perfectly reasonable expectation for distributed systems. Until now, we were forced to think about distributed technologies with low-level technical details such as the data objects to exchange, the programming language to communicate, and the platform constraints. The most basic scenario fulfilled by XML web services is that of providing some fundamental piece of business functionality for clients to use and define the interface at that high level.
This is not to say that there can never be web services to expose low-level fine-grained functionality as the web service's interface. Web services have the potential to solve integration issues with legacy systems. In certain cases, the ability to integrate with the legacy systems far outweighs the overhead of the roundtrip response time to low-level functions in that legacy system.