In my previous two blog posts I have described REST (here) and how the new Oracle SOA Suite 12c REST adapter can be used to call RESTful services (here). I recommend those articles to be read first if you're new to REST in order to better understand this article.
The newly introduced Oracle SOA Suite 12c REST adapter provides options for calling RESTful services but it can also be used to expose RESTful services. These exposed services can use XML or JSON as message exchange format. As described in the previous blog post, JSON support is implemented by implementing NXSD (Native Format Builder schema definition files, more information here) to describe the JSON message and make the transformation to and from XML possible. This XML can then be used as usual by the different components in a composite.