The earth- and ocean-science communities are developing the concept of a "system of systems" (www.epa.gov/geoss) for observing the earth and oceans. Related initiatives in the ocean sciences range from the application-oriented Integrated Ocean Observing System (IOOS) to the research-oriented Ocean Observatories Initiative (OOI). In an ideal world, all ocean observations would support the broad range of activities because all the systems would be interoperable. Such a "system of systems" will surely result from standardization of some kind. One challenge is that we already have many standards that address data-encoding formats, content metadata, protocols for communicating between computers, and ontology languages for knowledge representation. Two grass-roots community initiatives have aligned to make some concrete choices that will advance the "system of systems" concept: the Marine Metadata Interoperability (MMI) interoperability demo (www.marinemetadata.org) and the OpenIOOS interoperability test bed (www.openioos.org). Although they have substantial overlap, each initiative brings a complimentary set of experiences to the table. With funding from NSF and NOAA, the MMI project has been enabling the exchange, integration and use of marine data by emphasizing ontologies that employ the Web Ontology Language (OWL), in anticipation of the Semantic Web. With funding from the Office of Naval Research and NOAA, OpenIOOS participants have been demonstrating that "standards enable innovation" by leveraging web-service and data-model specifications developed by the Open Geospatial Consortium (www.opengeospatial.org). We present the lessons learned from this coordinated and combined effort.