Apache Sling is an innovative web framework built on top of the Java Content Repository (JCR), that uses OSGi for its component model and fosters RESTful application design. This presentation will showcase how the Apache Sling framework can be used to build a unified REST-based middleware for multiple data sources, such as MongoDB, Apache Cassandra, Apache Jackrabbit Oak or classical relational databases. In doing so it will present the benefits that come from a single Resource API over multiple data stores, both at the library level and at the HTTP boundary.