Different
Specification - Specifies how to make or supply something, materials, inspection and related items
Data sheet provide information (data) on the particular item you want (tag no, pressure rating, flange type and sizes, material, type of orifice etc ) and provides space for the vendor to fill in details that he needs to supply.
Lots of people mix these together or sometimes add the data sheet as an appendix to the specification, but much better to have as two separate documents
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.