Traditionally, DNS is a zone-based system in that all of the records for a zone are kept together in the same file. This has the benefit of simplicity and atomicity of zone updates, but when transposed to ENS can result in significant gas costs for simple changes. As a result, the resolver works on the basis of record sets. A record set is uniquely defined by the tuple (domain, name, resource record type), for example the tuple (example.com, www.example.com, A) defines the record set of A records for the name www.example.com in the domain example.com. A record set can contain 0 or more values, for example if www.example.com has A records 126.96.36.199 and 188.8.131.52 then the aforementioned tuple will have two values.