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This slide shows (in a simplified fashion) various steps in resolving a URN. That is, given a URN, how do you (a) find out information about the resource, and (b) how do you get a copy of the resource?
In the first step, the client parses urn:inet:netlib.org:pvm3, and determines that the URNis of type inet. It then consults a well-known subtree of DNS to find out about the organization of inet URNs. This is returned as an NAPTR record, which contains instructions as to how to parse this type of URN, as well as where to look next in order to resolve the URN.
In the second step, the client has learned that it must do a DNS query on the portion of the URN after inet: and before the next ":" character. The result of that query is a list of SRV records, which describe RCDS servers for that portion of the name space. (Additional NAPTR records could have been returned instead, indicating sub-delegation of some or all of the portions of URN space delegated to netlib.org.)
In the third step, the client picks one of the RCDS servers, asks it for information about the resource named by the URN, and gets back a description of that resource. Note that a LIFNis one of the fields in the description.
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