RDAP stands for Registration Data Access Protocol. It is a specification from the Internet Engineering Task Force (IETF) designed as a replacement for Whois data services for Domain Name Registries (DNRs) and Regional Internet Registries (RIRs). RDAP is specified in RFCs 7480, 7481, 7482, 7483, 7484, and 7485.

RDAP is an HTTP-based REST-style protocol. RDAP responses are specified in JSON. Whois is a text based protocol, utilizing a specialized protocol and port. Whois defines no queries or responses, and as a result the interaction with DNRs and RIRs can vary significantly.

Purists can fight over the meaning of a RESTful protocol, but RDAP meets the industry-accepted definition for a web-based RESTful protocol. It serves JSON over HTTP / HTTPS using URLs to distinguish various resources. The only HTTP methods used by RDAP are HEAD and GET.

Yes. ARIN has written a command-line RDAP client called NicInfo (https://github.com/arinlabs/nicinfo). In addition, there are clients available from DNSBelgium (https://github.com/DNSBelgium/rdap/tree/master/client) and CNNIC (https://github.com/cnnic/rdap/tree/master/rdap-client/src/main/java/org/restfulwhois/rdap/client) and CentralNIC (https://github.com/gitpan/rdapper).

It depends but given scripting tools such as curl, wget, and jsawk and services such as bootstrap servers you may be able to script together what you need to get information out of an RDAP.

A bootstrap server is a special type of RDAP server for aiding clients in the process finding an authoritative server to query (this is called bootstrapping). Query bootstrapping can be an expensive process for some clients, and a bootstrap server can alleviate that expense by pre-loading the bootstrapping information. To utilize a bootstrap server, an RDAP client simply sends RDAP queries and receives HTTP redirects to the authoritative server.

Yes. The ARIN bootstrap server is open sourced and can be found here: https://github.com/arinlabs/rdap_bootstrap_server.

Bootstrap files are JSON files specified in RFC 7484. IANA publishes these files: Autonomous System Numbers, IPv4 Allocations, IPv6 Allocations, and Domain Registries.