Sex?

A Valentine's Day special (yes a day early, I know, but better than a Friday 13th item). What data type should the "sex" attribute be in your database and what values should your form fields have?

No jokes such as the phrases (strings) "yes please" or "no thank you, we're British"... well, I guess a single character for gender of either "M" or "F" is often chosen. You might need to allow null for when this isn't known, or not divulged. Other people might use an alternative coding scheme.

Why not use a standard scheme?

You might be surprised to learn that there is an International Organization for Standardization (ISO) standard ISO/IEC 5218 on "Codes for the Representation of Human Sexes". And interestingly the technical committee have selected a one-character numeric code, with four (yes 4) valid options:

• 0 = Not Known
• 1 = Male
• 2 = Female
• 9 = Not Applicable

The standard points out (see the ISO 5218 entry on Wikipedia) the ordering is not meant to be significant, but UFO watchers and others will be pleased by the spare slots 3-8.

The current four values have also been incorporated as the sex data attribute in the P5 Guidelines for Electronic Text Encoding and Interchange by the Text Encoding Initiative (TEI) who develop and maintain a standard for the representation of texts in digital form. So, for a positive security models where the values passed to and from user input screens and in processing are the same as in the database, the acceptable values (also known as a "white list") is a set of integers: {0,1,2,9}.

The answer is therefore a small positive integer.