About   Help   FAQ
Glossary Term
Glossary Term Null
Definition In mathematics, a set with no members or of zero magnitude. If a field has a value of null, it means that the value is unknown. A null value is not the same as a value of zero. (To appreciate the difference, consider the terms "free" and "priceless." If something is free, it has a price of zero. If something is priceless, it has no known price. The difference between null and zero can be crucial; for example, when calculating the average value of a field among many records where one row contains a zero, the zero gets factored into the average. If the field has a null value, it does not get factored into the average.)

Contributing Projects:
Mouse Genome Database (MGD), Gene Expression Database (GXD), Mouse Tumor Biology (MTB), Gene Ontology (GO), MouseCyc
Citing These Resources
Funding Information
Warranty Disclaimer & Copyright Notice
Send questions and comments to User Support.
last database update
11/11/2014
MGI 5.20
The Jackson Laboratory