URI and Digital Object Unique Identifier
URI和数字对象唯一标识符*

As the infrastructure of digital library, digital object unique identifier is responsible for identifying, locating and managing of digital objects. This article discusses the types, component and principle of unique identifier, and analysis the demand of unique identifier from the logics,namespace,complexity,integratity and interoperability. Next ,the difference and relation have been compared among URI,URL and URN. Those syntax and identifying framework are also introduced. At last Cool URL is discussed in detail.