"if I learn, say, about 'A' today, tomorrow about 'B' and then learning about 'C' changes my perspective on the nature of 'A' or its relation to 'B' - re-classification will be needed. so while I can describe my knowledge today, tomorrow may be different; furthermore, relations may of course be conditional, with all that implies for management and structure. I really see piggydb as a tool primarily useful in the early stages of knowledge acquisition"