The first versions of most projects are self-contained applications. They work as-is, without any connection to other applications. It often isn't until a later release that there is focus on interoperability. They build import/export functionality into their applications or add webservices that allow other applications to interact with it.
While this is an important steps toward application interoperability, there is often an important step missing. Most interoperable applications lack one final feature that allows full seamless integration: data sourcing, or the ability to get the data it needs from elsewhere.