Properties and classifications - peterlegrand/SIPx GitHub Wiki
Classifications and properties are to link additional attributes to objects. The main difference between classifications and properties is that classificatioons support a multi level structure.
Both properities and classifications have values. These values are then related to the objects.
The following image shows the type of relation between objects and properties / classifications.

For content, persons, projects, and organizations. One object (e.g. one person) can have multiple properties related to that and each of these properties can be related to multiple objects. (Same for classifications.)
Processes in general have a limited number of properties and classifications (and their values) related to them.