Ask five people what "web services" are and you will likely get at least six different opinions. Because the term evokes such ambiguity, we need to set ground rules for this chapter and define what we mean by "web services". Therefore, for the purposes of this book, "web services" are the interactive exchange of messages from one system to another using the Internet as the network transport and HTTP/HTTPS as the messaging protocol. Message exchange transpires without human intervention and may be one-way—that is, called without an immediate response expected—or two-way.

Web services operate as producer/consumer systems where the producer—called the "service provider"—offers one or more "services" to the "consumer"—sometimes referred to as the "client". In the web services world, Internet-based service providers advertise and deliver service from locations throughout the Web. The Internet, and the Web in particular, serve as the highway over which potential web service clients travel to find service providers, make contact, and deliver products.

Service-oriented by design, OFBiz is a natural for building and deploying both web service clients and web service providers. Any OFBiz web application (webapp) may both consume web services and act as a web service provider within the same application or in an unlimited number of OFBiz webapps.

Within the web service producer/consumer model, service providers are responsible for accepting and validating requests for service and delivering the product. Consumers must find service providers, request service, and accept delivery of the product. There are a number of ad-hoc and formal standards that have evolved over the last few years to help facilitate the business of enabling web services, including, but not limited to, URL parameter passing, XML-RPC, and Simple Object Access Protocol (SOAP) based messaging. OFBiz provides built-in support with tools and integration points to make implementing both service provider and consumer web services a snap.