Initially, only one organization, DARPA, was responsible for handling the registration of domains. In the 1980s, WHOIS was standardized to look up domains and the information necessary for domain registration. There was a single centralized system for WHOIS queries. Because of that, it became effortless to look up such information. WHOIS, therefore, is a query and response protocol that queries databases which are responsible for the storage of assignees of IP addresses, domain names, and other internet resources, and registered users.
The referral WHOIS is just a continuation of the original version. Network Solutions first specialized it in 1994. Referral WHOIs is more scalable and hierarchical, so it gives the system a tree-like structure. Queries get transmitted to servers based on their hierarchical labels. It is more organized than the original WHOIS. It is possible to connect to any referral WHOIS server and request for a look-up. You will automatically get a notification of where to find the right server. RWHOIS is technically more functional than WHOIS, but most people have not adopted it yet. The referral features are different and services are mainly communicated through the Transmission Control Protocol.