11:21 Mar 22, 2011 

Product File - all the documents associated with the product (see CE marking directive for example) - translation of « Brief Produit »
Specifications - whatever the PRODUCT and other contract DELIVERABLES must comply with
Statement of Work - all the activities to be carried by the PRODUCER (developer in this case) besides the development and manufacturing of the product proper - tests, certification versus various agencies, documentation, etc. = maps into Cahier des Charges IMHO

11:09 Mar 22, 2011 

I agree with Callum's interpretation, that the product brief is referring to the "spécifications", but only in the first of your sample sentences. "Product brief" wouldn't be suitable to translate "spécifications" in the other sentences, and I feel that you need different solutions for the different uses, but don't know if that's possible in the context of your document - are the sentences in different sections? If you can, I'd use "specifications" for the 2nd sentence, "characteristics" for the third, "specifications" for the 3rd and "characteristics" for the 4th (with "specifications" for "cahier de charge"). The inconsistency this implies in the use of "spécifications" would not be unusual in French texts, long and bitter experience tells me...!