Another set of concerns is raised by the question of whether an identifier
be human readable or not or have implicit semantics.
The reason the DNS is such a hotbed of political intrigue is that there are
names like microsoft.com and there is an expectation that resolving such
identifiers maps to the companies that have been using the names as
trademarks.
Then there is the question of whether the identifier space is open or
closed. There are only 65535 valid IP ports and so assignment or well known
ports has different considerations to assignment of SRV tags which fulfill
the same function.
IP addresses are also identifiers and there are different considerations
for the different parts of the address. An IPv6 address must be globally
unique and the upper 64 bits have to map to some form of routing
information that is unique at a network level.
But another way to look at an IPv6 address is that it is a 64 bit address
and a 96 bit port space.