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In information management, persistence and availability are in constant tension. This tension has led to separate technologies for Uniform Resource Names (URNs) and Uniform Resource Locators (URLs). Meanwhile, Uniform Resource Identifiers (URIs) are designed to serve as both persistent names and available locations. This article explains how to use the current URI standards with XML technologies, gives a history of URNs and URLs, and provides a perspective on the tension between persistence and availability.