Status: Version 1 - 12th August 2015 Working Group Goals: The NIH BD2K bioCADDIE Metadata Working Group (WG) 3 is tasked to define a set of metadata specifications that support intended capability of the NIH BD2K Data Discovery Index prototype - as outlined in the bioCADDIE White Paper. This is a joint activity between bioCADDIE and CEDAR, another BD2K centre focused on metadata. This joint Metadata WG3 operates in two phases to produce a ‘core metadata’ (phase 1), designed to be future-proofed for progressive extensions to accommodate ‘domain-specific metadata’ for more specialized data types (phase 2), as needed. Scope of the Document: This document describes the process, the material reviewed (section 1 and Appendix I) and the use cases (section 2) used to identify an initial set of metadata elements and create a JSON schemata (section 3 and Appendix II); this work will be iteratively reviewed, following a test phase. Associated Material: This document, its appendixes and the associated code are available from the bioCADDIE Github repository and the bioCADDIE Metadata WG3 webpage; the latter also serves the original working files, the presentations and notes from the WG3 activities. The schemas and models in Appendix I are also listed in the BioSharing Collection for bioCADDIE. Intended Audience: This document is primarily aimed at the bioCADDIE Core Development Team that will implement and test this model; however this is also informative for other parties such as prospective data sources for the Data Discovery Index and developers of data harvesting and other tools. Contact: Questions and comments to Susanna-Assunta Sansone (WG3 chair) and WG3 members - adding them directly to the live Google document or sending them to biocaddie[at]ucsd.edu.