It assumed that whom ever you got the relationship will know how to get the other objects referenced by the relationship...
Why is that assumed? Shouldn’t the STIX/TAXII specs say how to do that? If it’s not consistent on how to do that then that is bad for consumers, and it seems like the point of the specs is to make it consistent for how to share information.
there isn't a delete operation in STIX
Why is there not a delete operation? How can the objects live in perpetuity?
In this case, they may choose to use a single "identity" for this group to produce their objects, and anyone in the group is allowed to use it.
Now there are no current technical measures to prevent you from doing this.
There are a couple of challenges with this approach. I’m curious how you plan to solve them.
1. Identity management
I have a lot of potential identities. Every combination of collaboration must be supported. That is exponential growth in the number of groups. While the number of groups is concerning the real heartburn will be when a user needs to select one. They will need to choose from a large set of groups.
For instance, consider the Navy UARC community. There is APL, PSU, UT, UW, and UH. As time goes I expect every possible combination of collaboration to develop. That means my “identity” for creating an object could be [(APL), (APL, PSU), (APL, UT), (APL, UW), (APL, UH), (APL, PSU, UT), (APL, PSU, UW), (APL, PSU, UH), … That’s kind of annoying for users to scroll through the long list to select.
2. Group selection
How do you know which group should be used? In the use case I gave the DHS analyst creating the first event has no idea who will contribute to the group. How would he know that only APL and FBI would contribute? He cannot know that and perhaps tomorrow another organization will want to contribute. Perhaps only DHS will contribute to the object.
I see a couple of options. He can either use an “everybody” group that allows anyone to contribute, or he can create a new group for each new SDO. The “everybody” group allows for anyone to contribute to the object. That is good, but all edits to the object will be attributed to “everyone” in which case you don’t know who made the object. That’s not good.
The other option is to create a new group for each new object. This would allow the group to add and expand members as more requests to contribute are received. The downside is that I now have a new group for each object, and the Identity must be further parsed so I can determine who is in the group. Group names become meaningless. The other downside is that I still don’t know who made what revision of the object. All I know is that someone in the group produced the last version.
Currently, they would need to contact the DHS to update their object
This is the alternate to the single identity approach. The biggest downside to this approach is object attribution. If I create an object then I would be hesitant to update it based upon a request from someone else unless I have a very close relationship with them. Going back to my example with DHS, FBI, and APL let’s assume FBI sends a request to DHS to change the object. Would DHS likely just accept the request? Probably not because anything in that object is attributed to them, and what are the chances that the DHS person that created the object knows and trusts the FBI agent making the request? I would be nervous of bad information being attributed to me. And APL being a consumer may want to know who added which parts to the object.