Data transformation after Linearization as per rules of Uhlig (1999)

As in Uhlig (1999), image
Xt(tilde) = Log X - LogXss
At the end of the linearization, the equations are left with Xt(tilde).
How should the data be organized, then?
Should it be Logged?
Uhlig mentions that “log of the variable’s deviation in relation to its steady state”.

Should we denote the variables in the as X for Dynare? OR as LogX-LogXss?

That depends. Have a look at Pfeifer(2013): “A Guide to Specifying Observation Equations for the Estimation of DSGE Models”