  Service-oriented High Level Architecture (SOHLA) refers to the high level
architecture (HLA) enabled by Service-Oriented Architecture (SOA) and Web
Services etc. techniques which supports distributed interoperating services.
The detailed comparisons between HLA and SOA are made to illustrate the
importance of their combination. Then several key enhancements and changes of
HLA Evolved Web Service API are introduced in comparison with native APIs, such
as Federation Development and Execution Process, communication mechanisms, data
encoding, session handling, testing environment and performance analysis. Some
approaches are summarized including Web-Enabling HLA at the communication
layer, HLA interface specification layer, federate interface layer and
application layer. Finally the problems of current research are discussed, and
the future directions are pointed out.
