Difference between SOA and Mashup Technology

Hi,

I am thinking about the differences of SOA and Mashup.

Both of them seam to have the same basic idea: combining existing applications / services / data to a new application / data view.

I would say, SOA is the basis architecture mashup are build on, but I'm not sure.

So, can you help me by defining the difference between SOA and Mashup?

Furthermore I am searching for interesting literature on Mashups, so I would appreciate if you can give me some advice.