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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Beyond Ontologies
 From: "Simon St.Laurent" <simonstl@s...> > >2) although the world is constantly changing, relationships need not > >so constantly change. For example...the *relationship* > ><#Simon> :sonOf _:1 between [you and your father] need not change > >(I haven't even assigned a URI to your father!) > > If all relationships changed all the time, we'd all be pretty confused. > The questions seem to arise around cases where changes in classification > possible, necessary, and often unpredictable. But relationships do change all the time. <#Simon> :sonOf_:1 is as good an example as any. I assume the 1 is intended to be the cardinality, so the relationship might be better named sonOfFather. But if your mother divorces and remarries, sonOfFather may no longer be many-to-one, but many-to-many. The latter probably better captures the relationship in the US, where roughly half of first marriages end in divorce. Wasn't so in the early part of the last century; it's a culturally induced change. Moreover, if you are cloned, you may not have a father, at all; which is quite a different thing than having a father but not knowing who he is. When this fairly recent eventuality, the examples of Vulcan and Jesus Christ notwithstanding, comes to pass, the cardinality of the father end of the relationship will become 0:n. Now consider the "type" of the father, nominally a male Person. Suppose a woman is impregnated by a sperm donor at a fertility clinic, where the identity of the donor is kept secret. This could be modeled as an unknown father, but in fact the identity of the biological father is known by the clinic, and the name of the clinic can serve as a surrogate for the father. If the type of the father is changed to the union of Person|Clinic, the parentage information is not lost. More children than one might suppose would benefit from this change. The point about relationships being neither homogeneous nor stable over time, in either number or type, nor universally applicable, has been well made by William Kent, e.g., in his classic "Limitations of Record-Based Information Models" ACM TODS paper. Many of Kent's examples are cases where relationships change to meet business needs, e.g., cars can be leased to departments as well as individual drivers, which are changes in business practice. I agree with the other points you made, but I hate to see you concede this one. Bob Foster 
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