# 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. | --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://chembl.gitbook.io/surechembl/chemical-search/structure-search-type.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.