Queries regarding WAS (Web Application Server)

Can any one tell about WAS, what is WAS and what are the uses in Integration?

What is use of abap and java engine in webas? If WAS has Integration Engine, can it have Integration Server to integrate two systems which can generate XML? From which SAP version it is available, will it come along with new version or shd it separately install? If I upgrade to new version greater than 4.7c will it automatically come with WAS?