The DSSP program standardizes protein secondary structure assignment.
DSSP is a database of secondary structure assignments (and much more)
for all protein entries in the Protein Data Bank (PDB). DSSP is also
the program that calculates DSSP entries from PDB entries. DSSP does
not predict secondary structure.
"A series of PDB related databases for everyday needs.", Robbie
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Nucleic Acids Research 2011 January; 39(Database issue): D411-D419.
"Dictionary of protein secondary structure: pattern recognition of
hydrogen-bonded and geometrical features.", Kabsch W, Sander C,
Biopolymers. 1983 22 2577-2637.