Generally, DNS represents to Domain Name System. But sometimes it is referred to Domain Name Service too. Anyhow, DNS system is a multi-level distributed naming system for whether computers, services, or any other resource, connected to the internet or else a private network. The main purpose of this system is to join together relevant information and domain names that are allotted to online participating entities. 
Most importantly, it gives meaningful form to domain names for the purposes of identifying networking equipments which are located on the different corners of the world. The DNS can spell out the function, practically of a database service. It can also define the DNS protocol, detailed specifications of the data structures and communication exchanges used in DNS as part of the IP suite.
But as an internet service, the key job of DNS is to transform the domain names of communicating devices into their IP addresses. With this system, it is possible to allocate domain names to different groups of the online resources plus users, independent of their (devices) physical locations. The reason of doing so is just to provide the convenience of understanding devices names over the internet. Domain names are available in the form of alphabetic so one can easily understand and even remember them since IP addresses are assigned to connected devices in the numerical form such as 208.77.189.167.
Whenever you will visit a website that means you are going to use a domain name. Therefore, only a domain name system can translate addressed domain name into its corresponding Internet protocol or IP address.
Certain advantages are associated with the DNS service like:
- no host table management is required
- especially designed for the internet and internet existence will be impossible without DNS system
DNS Construction
The Domain Name System provides a hierarchical structure either it is a matter of delegating naming authorities or maintaining the naming structure within DNS. But at the uppermost level of that hierarchy, you will observe the root domain “.” which is under the control of the IANA (Internet Assigned Numbers Authority). Moreover, root domain administration authority is given to IANA so beneath root, domains allocation can be made.
Delegating
The course of handing over a domain to any organizational body is known as delegating. That is also involved creating sub-domains by administrator of that domain etc. But a hierarchical delegation inaugurates at the DNS “root” while a fully qualified domain name, is acquired after writing simple names (attained as a result of tracing DNS hierarchy and sorting out each one name with a “.”) For example: oma.xyz.edu.au
Name-servers
The DNS maintenance is done by a distributed database that follows a client/server approach. But connecting nodes with a database are known as name-servers. But an “authoritative name server” mechanism is used to make the DNS both distributed and fault-tolerant system. There should be as a minimum one authoritative DNS server in every domain so that can distribute information regarding this domain as well as about the name-servers of any other domain, assisting to this domain. Authoritative name server is itself a name-server but that has an authority to provide configured (specified by the administrator) answers. There are two types of an authoritative name server:
- master server with original zone records copies
- slave server
Domain names will be registered with the help of domain name registrar. The duty of a primary name server is required while installing domain name at top level domain registry. And in any case, one secondary name server is also needed. Primary name server is called master name server and secondary name server is work as a slave server.