# Why do some crystal structure files not include bonds?

Why do some crystal structure files not include bonds (the atoms are just placed in the respective position in the cell without bonds between any atoms)? Shouldn't the bonds always be there? Also, where can I look up these bonds?

There are many algorithms for determining a bond graph from a set of atomic positions with varying "accuracy." I put the word in quotes because it's sometimes unclear what the goal should be when determining bond orders. For example, is a molecule in a keto or enol tautomer form? In some cases, the $\ce{C-O}$ bond is not clearly a single bond distance or a $\ce{C=O}$ distance. Maybe there's an ensemble average of both forms.
The standard seems to be if the CIF file looks more "ionic" (e.g., a salt like $\ce{NaCl}$) bonds probably will be ignored, but otherwise, bonds are interpreted from interatomic distances.