Any of these can be moved to middleware

Proxies - Local to Server Proxies can perform additional processing (or caching) between the server and the edge of the server network.
Proxies - Local to Client Proxies can perform additional processing or caching between the client application and the edge of the client network - or even any place in between.
Caching XML processing isn't always fabulously efficient, so caching results is a generally useful strategy.