DomainName is the domain name.
KeyTag contains the key tag value of the DNSKEY RR that validates this signature. The algorithm to generate it is here: https://tools.ietf.org/html/rfc4034#appendix-B
Algorithm is an integer identifying the algorithm used for signing. Valid values can be found here: https://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml
DigestType is an integer identifying the algorithm used to create the digest. Valid values can be found here: https://www.iana.org/assignments/ds-rr-types/ds-rr-types.xhtml
Digest is a digest of the DNSKEY RR that is registered with the registry.