  Standpoint EL is a multi-modal extension of the popular description logic EL
that allows for the integrated representation of domain knowledge relative to
diverse standpoints or perspectives. Advantageously, its satisfiability problem
has recently been shown to be in PTime, making it a promising framework for
large-scale knowledge integration.
  In this paper, we show that we can further push the expressivity of this
formalism, arriving at an extended logic, called Standpoint EL+, which allows
for axiom negation, role chain axioms, self-loops, and other features, while
maintaining tractability. This is achieved by designing a
satisfiability-checking deduction calculus, which at the same time addresses
the need for practical algorithms. We demonstrate the feasibility of our
calculus by presenting a prototypical Datalog implementation of its deduction
rules.
