External registry number

External Registry Number. A unique "external" identifier assigned to a structure, reaction, 3D model, assay, etc. The external registry number is usually unique across databases, and it can be used as a key to link data from one database or table to another. Any given database may have its own "internal" identifiers that may not be unique across databases. 

Cydodextrin CAS Registry Number Molecular formula Number of glucose units External Internal Aqueous solubility, M... 

Registry Number. A unique identifier assigned to a chemical structure or other piece of data when it is registered into a database. The registry number may be internal, primarily for use by the database search system, or external, to be used by chemists and to link the data to other databases and files. 

Furthermore, there is a piece of information which establishes the correspondence between the internal numbers of reactants and products and a detailed description of these structures in the example given here, the numbers 3, 4, 5 are associated with external identifiers (e.g., registry numbers) that point to entries in a file of structures. In this particular example (16), two of the molecules, 3 and 4, happen to refer to the same structure, i.e., their external identifiers e.g., their registry numbers, would be the same, but in the reaction they play a different role. Thus the external identifier would appear twice, but in a d erent context. 

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