"Theories of objecthood address two problems: the change problem and the problem of substance."
The answer to change problem is the answer to the following question, if object manifest themselves as cluster of properties... if you remove all the properties... what remains? According to substance theory, the answer is a substance (that which stands under the change)... if we apply this to Object Relational mapping... then.. the objectId (primary key) is the substance? Could this be used as a philosophical justification for the immutability of the primary key?
Then the text in the wikipedia continues: "Because substances are only experienced through their properties, a substance itself is never directly experienced." Is that a justification for never using the id (keeping it private)? Of course, there is another theory, the theory that since substance can not be experimented... then it doesn't exist, that is the "bundle theory".
In bundle theory all objects are merely a cluster of their properties and therefore... everything changes always... and no such thing as object ids/ primary keys really exist in the real world. This has an impact in relationships too, because we usually define a relationship as something that binds together 2 or more objects (at their substance level?)... but since object's substance doesn't actually exist then there isn't such thing as a "relationship" between two objects..
According to this relationships can only exist as something defined at the "property cluster level".. two (or more) objects aren't really related at the substance level... they simply "share a property" (is that why in SQL there isn't a way to make queries taking advantage of the integrity relationships? is "shared property" a better name for integrity relationships?)
And the thing gets worse: "Whether objects are just collections of properties or separate from those properties appears to be a strict dichotomy. That is, it seems that objects must be either collections of properties or something else." Is that the philosophical foundation for the "object/relational impedance mismatch"?
It seems that the conflict between a relational (bundle theory) and object (substance) worldview is there since way before a relational database or an object oriented language was invented...
I wonder what else could I learn from reading about this philosophical theories... (could there be a third one? is there a software programming paradigm for it?)