This document is intended as a step towards creating a globally-agreed upon standard for the Slice-based Facility Architecture, or SFA. At the time of writing, there exist some written SFA specifications, but as best we can tell they do not entirely correspond with written, currently functioning code. There also exist a number of functioning implementations, but these are not entirely documented. We take as our starting point SFA as it is implemented by SFAWrap (http://sfawrap.info), which is a generic SFA wrapper for testbeds. SFAWrap is used by, among others, the PlanetLab, SensLAB, and FEDERICA testbeds, as well as by the FITeagle tool. As such , it is deployed both in the FIRE initiative in Europe and in the GENI initiative in the United States. We dub this version the Open SFA specification, as we open it for discussion and contribution to stakeholders worldwide. This draft can be found on the OpenSFA website (http://opensfa.info), and those who wish to participate are invited to join the mailing list discuss@opensfa.info [mailto:discuss@opensfa.info].