why coding strand is so important?

[bioinfo]

i want to creat program for transcription .
I know programming but confusion is that what should change means
which sequence should taken as query from NCBI.
then what basepair should change
1) T to U or
2) "A" to "U","C" to "G" and so on(Complementary)

which way is true.
In NCBI seq. are coding or template.



If NCBI contains coding strand then why?
Because as per my knowledge transcription is done from template strand.
Are all fasta nucleotide sequence files has sequences of coding strand??
&what is about genomic seq. files???

[JackBean]

wright? Wrights are dangerous!

Anyway, the DNA sequences at databases are of coding strand, AKA they have the same sequence as transcript except of T/U (this is not that much about programming;)