  Modelling and Simulation as a Service (MSaaS) is a promising approach to
deploy and execute Modelling and Simulation (M&S) applications quickly and
on-demand. An appropriate software architecture is essential to deliver quality
M&S applications following the MSaaS concept to a wide range of users. This
study aims to characterize the state-of-the-art MSaaS architectures by
conducting a systematic review of 31 papers published from 2010 to 2018. Our
findings reveal that MSaaS applications are mainly designed using layered
architecture style, followed by service-oriented architecture, component-based
architecture, and pluggable component-based architecture. We also found that
interoperability and deployability have the greatest importance in the
architecture of MSaaS applications. In addition, our study indicates that the
current MSaaS architectures do not meet the critical user requirements of
modern M&S applications appropriately. Based on our results, we recommend that
there is a need for more effort and research to (1) design the user interfaces
that enable users to build and configure simulation models with minimum effort
and limited domain knowledge, (2) provide mechanisms to improve the
deployability of M&S applications, and (3) gain a deep insight into how M&S
applications should be architected to respond to the emerging user requirements
in the military domain.
