> For the complete documentation index, see [llms.txt](https://chembl.gitbook.io/unichem/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://chembl.gitbook.io/unichem/submission-of-data-to-unichem/rules-for-loading.md).

# Reasons for data omission

UniChem needs a way to calculate Standard InChI. Depending on whether a tabular or SDF file is provided, the calculation is derived from either the SMILES string or the Molblock. For the chemical calculation RDKit is used. If during the loading process, UniChem can not calculate the Standard InChI, that compound will be omitted.