1. A method reliable computer-implemented mashup of data in communications between a client and at least one service, comprising the steps of: intercepting, by an intercepting module, a data update request comprising client modifiable data submitted by a client browser to at least one service of a plurality of services providing mashup page data for a mashup data page before said request arrives at said at least one service, wherein said client browser is in a client computer; generating consistency rules by analyzing the mashup page data; performing consistency validation on client modifiable data in said request by a consistency validator using consistency rules to produce a validity determination indicating whether client modifiable data was modified at the client; and forwarding, by a forwarding module, said request from said consistency validator to said at least one service in response to said validity determination, wherein the consistency rules are generated by (i) analyzing the Document Object Model (DOM) tree of the mashup page, and (ii) analyzing mashup logic in the mashup page data.