A virtual, centralized and structured database or portal that allows one to list, do a structured search, and to identify and retrieve metadata and possibly data that are distributed around a network. Registries are places where various types of resources are indexed and made visible and available for use throughout a community; they do not include clustered servers or depend on harvesting approaches to access their contents. Some survey organizations register measures (question wording and response options, for example) in order to standardize the way they elicit information from respondents. The implication is that there is one correct way for an organization to measure, say, income. Examples of DDI registries could be question banks, concept banks, social science data survey catalogs, and variable banks.