One popular notion of a (Scott-Ershov) domain is defined as a bounded complete algebraic cpo. Such an abstract a definition is not always so helpful for beginners. The speaker found recently that there is an easy-to-construct domain of countable semilattices giving isomorphic copies of all countably based domains. This approach seems to have advantages over both the so-called "information systems" and the more abstract lattice/ topological definitions, and it makes the finding of solutions to domain equations and models for the lambda-calculus very elementary to justify. The "domain of domains" also has a natural computable structure in this formulation. Built on top of this construction is a modeling of Martin-Löf type theory.