DOI Namespace > Syntax of the DOI Name > Considerations about the Use of Check Digits in DOI Names

A DOI name is an opaque string. The DOI System does not itself make use of check digits. This is deliberate, for a number of reasons:

•ability to include an existing identifier string as a prefix in a DOI without any alteration: some common strings like ISO identifiers already have a check digit in them which act as aids to readability or keyboard data entry in the absence of any automated protocol correction;

•performance considerations if a check sum is calculated at each resolution;

•identifier schemes such as URL have no check digit: the underlying TCP/IP protocol they use has an error-correction component. This aids creation and use.

However, other applications may make use of check digits, so a checksum digit may be inserted into a DOI name if it would be useful for some other application. Use of checksums in a particular DOI System application can be introduced as a rule of that application by the Registration Agency concerned. An example is the EIDR application, where the check character is computed only over the DOI suffix. It does not include the prefix because if the prefix is wrong, it is highly probable that the DOI name will go to an incorrect resolution system anyway. The EIDR registry separately validates the prefix of any DOI name sent through its API.