The domain name space is a name space that shows:
- a basic tree structure (ie hierarchical)
- where the hierarchy levels are separated by the dot character .
Each node on the tree corresponds to a resource set (which may be empty).
The term domain name is used to refer to the name of a node but has no relation to the DNS because a name can also be used in other mean such as mail addressing.
See Domain Name
Each node has a label, which is zero to 63 octets in length.
The domain name of a node is the list of the labels on the path from the node to the root of the tree.
By convention, the labels that compose a domain name are printed or read left to right, from the most specific (lowest, farthest from the root) to the least specific (highest, closest to the root).
The root node has a null string for label.
Syntax as specified by the rfc: 1)
<domain> ::= <subdomain> | " " <subdomain> ::= <label> | <subdomain> "." <label> <label> ::= <letter> [ [ <ldh-str> ] <let-dig> ] <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str> <let-dig-hyp> ::= <let-dig> | "-" <let-dig> ::= <letter> | <digit> <letter> ::= any one of the 52 alphabetic characters A through Z in upper case and a through z in lower case <digit> ::= any one of the ten digits 0 through 9