What is the job of a producer during the making of a movie? And what is the job of an Executive Producer?

Question by E3_E3: What is the job of a producer during the making of a movie? And what is the job of an Executive Producer?
Please post sources if you have them.

Best answer:

Answer by J
http://www.ehow.com/about_4614369_what-job-executive-producer.html

http://www.prospects.ac.uk/p/types_of_job/television_film_video_producer_job_description.jsp

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