  A Web API (WAPI) is a type of API whose interaction with its consumers is
done through the Internet. While being accessed through the Internet can be
challenging, mostly when WAPIs evolve, it gives providers the possibility to
monitor their usage, and understand and analyze consumers' behavior. Currently,
WAPI usage is mostly logged for traffic monitoring and troubleshooting. Even
though they contain invaluable information regarding consumers' behavior} they
are not sufficiently used by providers. In this paper, we first consider two
phases of the application development lifecycle, and based on them we
distinguish two different types of usage logs, namely development logs and
production logs. For each of them we show the potential analyses (e.g., WAPI
usability evaluation, consumers' needs identification) that can be performed,
as well as the main impediments, that may be caused by the unsuitable log
format. We then conduct a case study using logs of the same WAPI from different
deployments and different formats, to demonstrate the occurrence of these
impediments and at the same time the importance of a proper log format. Next,
based on the case study results, we present the main quality issues of WAPI log
data and explain their impact on data analyses. For each of them, we give some
practical suggestions on how to deal with them, as well as mitigating their
root cause.
