  Today's permissioned blockchain systems come in a stand-alone fashion and
require the users to integrate yet another full-fledged transaction processing
system into their already complex data management landscape. This seems odd as
blockchains and traditional DBMSs share large parts of their processing stack.
Thus, rather than replacing the established data systems altogether, we
advocate to simply 'chainify' them with a blockchain layer on top.
  Unfortunately, this task is far more challenging than it sounds: As we want
to build upon heterogeneous transaction processing systems, which potentially
behave differently, we cannot rely on every organization to execute every
transaction deterministically in the same way. Further, as these systems are
already filled with data and being used by top-level applications, we also
cannot rely on every organization being resilient against tampering with its
local data.
  Therefore, in this work, we will drop these assumptions and introduce a
powerful processing model that avoids them in the first place: The so-called
Whatever-LedgerConsensus (WLC) model allows us to create a highly flexible
permissioned blockchain layer coined ChainifyDB that (a) is centered around
bullet-proof database technology, (b) makes even stronger guarantees than
existing permissioned systems, (c) provides a sophisticated recovery mechanism,
(d) has an up to 6x higher throughput than the permissioned blockchain system
Fabric, and (e) can easily be integrated into an existing heterogeneous
database landscape.
