A New Look at Schema Instance Recoverability with the Notion of ´Information Carrying´

In database schema transformation, whether the instances of a schema may be recovered from those of another is a question, which seems profound., and yet having not been well investigated. We shed some light on it. In the literature, the work that is closest to this question is the notion of `relevant information capacity´, which is concerned with whether one schema may replace another without losing the capacity of the system in storing data. We observe that this is over simplistic and we reveal that it is the phenomenon that one or more instances of a schema can tell us truly what an instance of another schema is that underpins a convincing answer to this question. This is a matter of one thing carrying information about another. This requires looking at detailed levels of informational relationships, namely random events and particulars of random events.