> For the complete documentation index, see [llms.txt](https://chembl.gitbook.io/surechembl/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/surechembl/chemical-search/structure-search-type.md). # Structure search type There are several approaches to locating chemical structures within patent documents. SureChEMBL focuses on the three most popular methods. By definition, the examined molecule within a patent is called a ***target***, the structure we seek is called a ***query***, and a target molecule matching the query structure is called a ***hit***. The following chemical searches are available: | Search type | Description | | ------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Substructure |

Chemists are most often interested in Substructure search, that is, whether a target structure contains the query structure within it.

Note: If special molecular features are present on the query (eg. stereochemistry, charge, etc.), only those targets containing the feature are considered hits. However, if a feature is missing from the query, it is not checked and targets without that feature may appear as hits.

| | Similarity |

A Similarity structure search looks for target structures that are similar to the query structure. The similarity concept implemented is based on hashed binary chemical fingerprints derived using a Tanimoto metric. That is to say, the presence of molecular features are recorded for both the query and the target and then compared using a standard formula.

Note: See Tanimoto coefficient and fingerprint generation for a complete description of the concept and method used.

Note: If you choose Similarity as your search type, you will be prompted to provide a Tanimoto coefficient between 50 and 100%.

| | Identical | In an ***Identical structure search,*** all molecular features need to be equal (e.g. a non-stereo query will only match a non-stereo target). | | Connectivity | ***Connectivity search*** retrieves compounds with common atomic connectivity but differing stereochemistry or isotopic forms. |