  Natural language processing supported requirements engineering is an area of
research and development that seeks to apply NLP techniques, tools and
resources to a variety of requirements documents or artifacts to support a
range of linguistic analysis tasks performed at various RE phases. Such tasks
include detecting language issues, identifying key domain concepts and
establishing traceability links between requirements. This article surveys the
landscape of NLP4RE research to understand the state of the art and identify
open problems. The systematic mapping study approach is used to conduct this
survey, which identified 404 relevant primary studies and reviewed them
according to five research questions, cutting across five aspects of NLP4RE
research, concerning the state of the literature, the state of empirical
research, the research focus, the state of the practice, and the NLP
technologies used. Results: 1) NLP4RE is an active and thriving research area
in RE that has amassed a large number of publications and attracted widespread
attention from diverse communities; 2) most NLP4RE studies are solution
proposals having only been evaluated using a laboratory experiment or an
example application; 3) most studies have focused on the analysis phase, with
detection as their central linguistic analysis task and requirements
specification as their commonly processed document type; 4) 130 new tools have
been proposed to support a range of linguistic analysis tasks, but there is
little evidence of adoption in the long term, although some industrial
applications have been published; 5) 140 NLP techniques, 66 NLP tools and 25
NLP resources are extracted from the selected studies.
