We examine the concept of Quality of Information (QoI); the idea that networked data systems can better support users if they have a notion of what the data is being used for. We argue that to judge quality it is as important to know how the data was processed as it is to know what the data says. We model QoI systems as a structure that enforces the annotation of data creating processes with the data they produce. Furthermore, we model the evaluation of quality as functions that map information into a closed and bounded, totally ordered set. We define addition and multiplication operations which make a subring out of the set, thus allowing data composed of multiple pieces of information to be evaluated as sums and products of its components. Finally, we give an example to show how our model supports the delivery of high quality information.