Method for extraction of data by a server in a database of data that is watermarked according to a reversible watermarking mechanism defined by watermarking metadata (M) so as to a dissimulate a mark, said database comprising tuples comprising at least one watermarked attribute (A n ), said method comprising: • a step (E1) of receiving a first extraction request (R1; R11; R12; R13; R14; R15) from a client terminal to select a first set of tuples from said database , according to at least one initial selection condition relating to the value (A) of said at least one watermarked attribute (A n ) with respect to at least one threshold S; • a step (E3) of obtaining, from said first extraction request, a second extraction request (R2; R21; R22; R23; R24; R25) to select a second set of tuples comprising the attributes of the first set of tuples including said at least one watermarked attribute to which said at least one selection condition relates, said second extraction request comprising at least one selection condition obtained by transforming said at least one initial selection condition relating to at least one watermarked attribute A; • an extraction step (E5), during which the tuples of said second set (E) are extracted from said database according to the second extraction request; • a de-watermarking step (E7), during which the tuples of said second set of extracted tuples (E) are de-watermarked (E') according to the watermarking metadata (M); • a step (E9) of obtaining, from the first extraction request (R1), a third request (R3; R31; R32; R33; R34; R35) to select a third set of tuples from said second set of de-watermarked tuples (E'), said third request comprising said at least one initial selection condition; • a filtering or transformation step (E11), during which the third request is applied to the second set of de-watermarked tuples (E'); and • a step (E15) of sending results (R) from the filtering or transformation step (E11) to the client. • a step (E1) of receiving a first extraction request (R1; R11; R12; R13; R14; R15) from a client terminal to select a first set of tuples from said database , according to at least one initial selection condition relating to the value (A) of said at least one watermarked attribute (A n ) with respect to at least one threshold S; • a step (E3) of obtaining, from said first extraction request, a second extraction request (R2; R21; R22; R23; R24; R25) to select a second set of tuples comprising the attributes of the first set of tuples including said at least one watermarked attribute to which said at least one selection condition relates, said second extraction request comprising at least one selection condition obtained by transforming said at least one initial selection condition relating to at least one watermarked attribute A; • an extraction step (E5), during which the tuples of said second set (E) are extracted from said database according to the second extraction request; • a de-watermarking step (E7), during which the tuples of said second set of extracted tuples (E) are de-watermarked (E') according to the watermarking metadata (M); • a step (E9) of obtaining, from the first extraction request (R1), a third request (R3; R31; R32; R33; R34; R35) to select a third set of tuples from said second set of de-watermarked tuples (E'), said third request comprising said at least one initial selection condition; • a filtering or transformation step (E11), during which the third request is applied to the second set of de-watermarked tuples (E'); and • a step (E15) of sending results (R) from the filtering or transformation step (E11) to the client. <EOS>