do applications always need an UI

Web Service clients. Some business applications require no user interface at all. They exist to interconnect with other business partners' applications that may provide their own user interface. For example, consider a scenario where Dell Computer Corporation needs to procure Intel chips to assemble and distribute desktop computers. Here, Intel could expose an Order Parts Web Service that enables the Dell Web Service client to order chips. In this case, the Intel system does not provide a graphical user interface per se, but rather it provides a Web Service interface.