Editing Chemical database (section)

=== Substructure ===
{{Main|Substructure search}}
[[File:Lenalidomide substructures.svg|thumb|The drug [[lenalidomide]] contains substructures [[isoindoline]] (red) and [[glutarimide]] (blue)]]
Chemists can search databases using parts of structures, parts of their [[IUPAC]] names as well as based on constraints on properties. Chemical databases are different from other general purpose databases in their support for substructure search, a method to retrieve chemicals matching a pattern of atoms and bonds which a user specifies. This kind of search is achieved by looking for [[subgraph isomorphism]] (sometimes also called a [[monomorphism]]) and is a widely studied application of [[graph theory]].<ref name=Currano>{{cite book |doi=10.1039/9781782620655-00109  |chapter=Chapter 5. Searching by Structure and Substructure |title=Chemical Information for Chemists |date=2014 |last1=Currano |first1=Judith N. |pages=109–145 |isbn=978-1-84973-551-3 }}</ref><ref name=Ullmann>{{cite journal |doi=10.1145/321921.321925 |doi-access=free |title=An Algorithm for Subgraph Isomorphism |date=1976 |last1=Ullmann |first1=J. R. |journal=[[Journal of the ACM]] |volume=23 |pages=31–42 }}</ref><ref name=Warr2011>{{cite journal |doi=10.1002/wcms.36 |title=Representation of chemical structures |date=2011 |last1=Warr |first1=Wendy A. |journal=WIREs Computational Molecular Science |volume=1 |issue=4 |pages=557–579 }}</ref>

Query structures may contain bonding patterns such as "single/aromatic" or "any" to provide flexibility. Similarly, the vertices which in an actual compound would be a specific atom may be replaced with an atom list in the query. [[Cis–trans isomerism|''Cis''–''trans'' isomerism]] at [[double bond]]s is catered for by giving a choice of retrieving only the [[E–Z notation|E form]], the [[E–Z notation|Z form]], or both.<ref name=Currano/><ref name=Pubchem>{{cite web |url=https://pubchem.ncbi.nlm.nih.gov/search/help_search.html |title=PubChem Structure Search |website=pubchem.ncbi.nlm.nih.gov |access-date=2024-08-01}}</ref>