  In software development teams, developer turnover is among the primary
reasons for project failures as it leads to a great void of knowledge and
strain for the newcomers. Unfortunately, no established methods exist to
measure how knowledge is distributed among development teams. Knowing how this
knowledge evolves and is owned by key developers in a project helps managers
reduce risks caused by turnover. To this end, this paper introduces a novel,
realistic representation of domain knowledge distribution: the ConceptRealm. To
construct the ConceptRealm, we employ a latent Dirichlet allocation model to
represent textual features obtained from 300k issues and 1.3M comments from 518
open-source projects. We analyze whether the newly emerged issues and
developers share similar concepts or how aligned the developers' concepts are
with the team over time. We also investigate the impact of leaving members on
the frequency of concepts. Finally, we evaluate the soundness of our approach
to closed-source software, thus allowing the validation of the results from a
practical standpoint. We find out that the ConceptRealm can represent the
high-level domain knowledge within a team and can be utilized to predict the
alignment of developers with issues. We also observe that projects exhibit many
keepers independent of project maturity and that abruptly leaving keepers harm
the team's concept familiarity.
