The proven ability of Bitcoin and other cryptocurrencies to operate autonomously on the trustless Internet has sparked a big interest in the underlying technology-Blockchain. However, the portage of Blockchain technology outside its initial use case led to the inception of new types of Blockchains adapted to different specifications and with different designs. This unplanned evolution resulted in multiple definitions of what a Blockchain is. The technology has diverged from its baseline (Bitcoin) to the point where some systems marketed as "blockchain" share only a few design concepts with the original Blockchain design. This conceptual divergence alongside the lack of comprehensive models and standards made it difficult for both system designers and decision-makers to clearly understand what is a blockchain or to choose a suitable blockchain solution. To tackle this issue, we propose in this paper "DCEA" a holistic reference model for conceptualizing and analysing blockchains and 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.