On the NSF requirement

The (very general) guidelines for data management plans are presented in Section j. Special Information and Supplementary Documentation of the Grant Proposal Guide, Chapter II - Proposal Preparation Instructions. They are the second bulleted item in the linked section.

Data management requirements and plans specific to the Directorate, Office, Division, Program, or other NSF unit, relevant to a proposal are available at: http://www.nsf.gov/bfa/dias/policy/dmp.jsp. If guidance specific to the program is not available, then the general requirements listed at the first web site (i.e., in Section j, linked above) apply.

A break-down of the basics from the Research Remix blog, quoting the NSF documentation and with links to helpful references.

See also NSF Data Management & Sharing FAQs.

On Data Management

The Library's Data Management Committee has compiled this toolkit to help researchers understand the issues involved in data management and provide resources for formulating data management plans. See the links at left for specific sections.