Ho to make data source web method execute once per a report?

My report works with XMLDP data provider and obtains source data as a

result of a web method call. This memthod returns all data necessary

for the report. Thus, all of about 20 report datasets query the same

web method with the same parameters and then select appropriate data

with different ElementPath expressions. It's so inefficient and

time-consuming! I cant have respective web method for every dataset.

How can I configure SSRS to call web method only once while the report

is executing? Or how can I leverage the performance at all?I seem to have founed the solution. I've configured report datasource to execute in single transaction and extra marked the source web method with [WebMethod(CashDuration=%TIME)] attribute. Hence, the report datasets call the web method one after another and the method is actually executed only once if %TIME value is more than report processing time. That's what I need!