The Learning Registry is an effort jointly sponsored by the Department of Education and the Department of Defense. The effort began in 2010 and creates a set of technical protocols for the exchange of data in support of educational goals by multiple providers. It is not a portal, but a platform for aggregating metadata and other data about learning objects.
NSDL publishes its learning object metadata to the Learning Registry in LRMI/JSON-LD format and paradata in LR paradata 1.0 format. Additions, changes, and deletions are published on a weekly basis.
The NSDL first published a static snapshot of its metadata to the Learning Registry in NSDL DC format in 2011. These were superseded in November 2013 when NSDL began publishing using LRMI/JSON-LD and LR paradata 1.0 formats.
As of November 2013:
Learning resource metadata are published in LRMI/JSON-LD format and include standards tagged with ASN URIs, CCSS URIs, CCSS dot notation, and other standards identifier schemes; Grade Level (typicalAgeRange), Audience, Resource Type, and others.
Paradata are published in LR Paradata 1.0 format and include user comments (full text) and usage summaries (no of times viewed, favorited, commented, average star rating, etc).
Example paradata with usage summary:
http://node01.public.learningregistry.net/slice?any_tags=oai:nsdl.org:2200/20120131140505697T
NSDL has been collaboratively engaged with the Learning Registry from its inception, along with additional collaborators, Butte County Office of Education/CADRE, Navigation North, and others.