Content centric applications have high requirements on their storage backends. Traditionally, many applications have built their own content storage logic on top of relational or NoSQL databases. The idea of a content repository is to decouple this logic from the actual application. The same idea can be applied to the editing interface. Decoupling a content management system allows to focus on ones strong areas and for the other tasks reuse existing tools.Read more on the concept of decoupled content management on decoupledcms.org.
In the long run, the clean separation between storage, application and editing tools allows for better reuse and leads to better performance, scalability and usability, as each part of the architecture can be highly optimized. This article presents the PHPCR standard that provides a content repository, but the concept applies to other layers like the editing interface as well.