identifier As a command 17 categories below identifier Narrow by persistent-identifier 3 code 2 computer-address 2 uniform-resource-identifier 2 agent 1 character-string 1 cognition 1 collection 1 concept 1 data-type 1 group 1 idea 1 name 1 set 1 persistent-identifier 3uniform-resource-identifier 2content-identifierdata-descriptordigital-object-identifierdomain-namefile-pathfilename-extensionforeign-keyhostnameip-addressmac-addressnamespaceprimary-keyuniform-resource-nameuniversally-unique-identifierurl