This task is a follow-up to a conversation on Wikidata's project chat.
Sometimes, it is necessary to know details about a statement group. Unfortunately, Wikibase does not provide a way to do this.
I am certain that the list of themed areas in the has part property of Universal Studios Florida is complete (in the current sense, not the historical one as themed areas like "Amity Island" are missing, but no longer exist). I am also confident that the list of themed areas in the has part property of Epcot is incomplete (but can be completed). I am aware of this, but there is no way to express this in Wikidata to other users and machines. Therefore, it's impossible to be able to answer: How many themed areas does each theme park have? You might think you have the answer based on what is provided (you may assume the property is complete), and not realize that you don't. For these two results you would have 8 and... >1 would be the proper answer. If you were to assume that it is always incomplete, then you would never be able to answer this question, even if all of the theme parks had a complete set, there would be no way to know they were complete.
Perhaps when statement groups need properties, an intermediate object (like schema.org's Role) could be added so those properties can be added to the statement group itself.
- A common work around on Wikidata is to create another property that has the count of items. For instance number of seasons and season or number of children and child, the former informing the completeness of the latter.
- Another common workaround is to create list items like reasons for deprecation that could have an expected completeness property