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Domain name system (DNS) is a hierarchical naming system built on a distributed database. This system transforms domain names to IP addresses and makes it possible to assign domain names to groups of Internet resources and users, regardless of the entities' physical location.
The domain name system includes a tree of domain names. Every leaf, or node, in the tree has zero or more resource records, which include information associated with the domain name. The tree further subdivides into zones, starting at the root zone. DNS zones may have one domain, or many domains and subdomains depending on the administrative authority delegated to managers. The client side of DNS, the DNS resolver, is responsible for initiating and sequencing queries that lead to full resolution of the resources sought. These queries are either recursive or nonrecursive.
DNS assigns domain names and maps the names to IP addresses by designating an authoritative name server for each domain. These servers are responsible for particular domains and can assign the authoritative name servers to subdomains. As a result of this process, DNS is both distributed and fault tolerant.
DNS stores a list of mail servers that accept email for an Internet domain. Identifiers such as radio frequency identification tags, universal product codes (UPCs), international characters in email addresses and host names also use DNS.