15.2.6. Implicit perspectives
In Figure 1 we presented two user roles with a perspective on the same role R, that did not see each other. We speculated that if one of those roles modified R, the other would never know. Thus, to synchronize properly, we must add a perspective from the modifying user to the other user. In Figure 11 we’ve reiterated that situation. We’ve drawn the context as well and we’ve indicated which of the users modifies the role R (by starting the perspective arrow with a closed circle). We’ve also drawn the inverted query that originates in R and leads to user role 2. This is the inversion of 2’s perspective on R.
Figure 11. User role 1 can modify role R. User role 2 can ‘see’ role R. This implies that 1 should send his modifications of R to 2, hence has an implicit perspective on 2.
As shown in the figure, we might consider the combination of the modifying perspective on R and the inverted perspective from R to be an implicit perspective of user role 1 on user role 2. In other words, we interpret this situation as if there really was a perspective of 1 on 2.
Consider the impact of that interpretation. It would mean that as soon as an instance of 2 was added to context C by some role 3 (not drawn), 3 would send that instance to 1, because 1 has a perspective on role type 2.
Similar reasoning applies to the inverse situation that arises as an instance of 1 is added to C. This new peer would receive the user role instance of 2.
In other words, under this interpretation of inverse perspectives, there is no need for explicit perspectives on user roles for the good of synchronization.
However. It would constitute a security breach as we’ve discussed in the paragraph Hidden peers. In the example of the peer-reviewed article, the identity of the Authors would be disclosed to the Reviewers, and the other way round (as their comments on the Article would be directly sent by their PDR’s to the Authors’). We may be able to limit the disclosed information to just that needed to send transactions (omitting the identities and other personal information). However, the address information that must be exchanged could be a real giveaway.
For this reason we will not interpret inverted perspectives as implicit user perspectives.