  The presented work continues the line of recent distributed computing
communityefforts dedicated to the theoretical aspects of blockchains. This
paper is the rst tospecify blockchains as a composition of abstract data types
all together with a hierarchyof consistency criteria that formally
characterizes the histories admissible for distributedprograms that use them.
Our work is based on an original oracle-based constructionthat, along with new
consistency deffnitions, captures the eventual convergence processin blockchain
systems. The paper presents as well some results on implementability ofthe
presented abstractions and a mapping of representative existing blockchains
fromboth academia and industry in our framework.
