This document discusses leveraging the DDI (Data Documentation Initiative) model for linked statistical data in the social, behavioral, and economic sciences. It outlines how the DDI was developed as an ontology, including using use cases to identify important elements to model and mapping existing DDI-XML documents to DDI-RDF. A key use case is discovering microdata connected across multiple studies based on dimensions like time, country, and subject. The document walks through examples of queries this ontology would support, such as finding questions associated with a concept or the maximum value of a variable. It concludes by identifying some open issues to address in the DDI ontology.