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Typically, scheme-based services are designed as silos ("walled gardens") to serve a particular identifier type (eg, Handle, DOI, or PURL). Each silo does performs the same basic things main functions – mapping names (identifiers strings) to things (objects or metadata). Excluding all but one type of identifier string may help to capture markets, but it's wasteful and non-inclusive. It requires building the same set of services over and over for each type and violates basic principles of openness, so the N2T (Name-to-Thing) resolver and EZID (identifiers made easy) management interface were designed to work with all identifiers. Work put into any new feature can be efficiently leveraged across all types, which sometimes creates surprising flexibility; for example, ARKs are often stored in EZID with "DOI metadata", and every DOI stored in N2T can benefit from "ARK resolution features" such as inflections and suffix passthrough, which are not available via the main DOI resolver (doi.org).
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Although N2T (Name-to-Thing) is a resolver originally built for ARKs, principles of openness prevented it from becoming just another DOI/Handle/PURL-type silo, which all perform the same basic main functions. Thus the "global ARK resolver" also resolves DOIs, Handles, PURLs, URNs, and 600 other types of identifier.
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