Bitcoin's notable success at operating autonomously as a global peer-to-peer network opened the door to a new revolutionary class of distributed systems: blockchain. However, with the rising popularity of this new paradigm, the concept of blockchain shifted greatly to the point where many systems marketed as "blockchain" without sharing the key components introduced by Bitcoin. It has therefore become quite challenging for system designers or decision-makers to achieve a sufficient understanding of different types of existing blockchains or to design and adopt the correct blockchain solution. To overcome this problem, we propose DCEA a holistic reference model for conceptualizing and closely examining blockchains and globally distributed ledger technologies (DLT) using a layer-wise framework that envisions all these systems as constructed of four layers: the data, consensus, execution and application layers.