  Digital Twin (DT) technology is far from being comprehensive and mature,
resulting in their piecemeal implementation in practice where some functions
are automated by DTs, and others are still performed by humans. This piecemeal
implementation of DTs often leaves practitioners wondering what roles (or
functions) to allocate to DTs in a work system, and how might it impact humans.
A lack of knowledge about the roles that humans and DTs play in a work system
can result in significant costs, misallocation of resources, unrealistic
expectations from DTs, and strategic misalignments. To alleviate this
challenge, this paper answers the research question: When humans work with DTs,
what types of roles can a DT play, and to what extent can those roles be
automated? Specifically, we propose a two-dimensional conceptual framework,
Levels of Digital Twin (LoDT). The framework is an integration of the types of
roles a DT can play, broadly categorized under (1) Observer, (2) Analyst, (3)
Decision Maker, and (4) Action Executor, and the extent of automation for each
of these roles, divided into five different levels ranging from completely
manual to fully automated. A particular DT can play any number of roles at
varying levels. The framework can help practitioners systematically plan DT
deployments, clearly communicate goals and deliverables, and lay out a
strategic vision. A case study illustrates the usefulness of the framework.
