Major Arcana 10: The Copy
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In the traditional Tarot, the 10th trump card is the Wheel of Fortune. For computers, it is the copy.
Information has a location, but those locations are ephemeral and changing. To use data from your disk, it must be copied into memory; when you retrieve a document on over the Internet, you reproduce the entire document on your own computer. Our intuitions about identity start to fail under these conditions - is there an original version of this or that information? How does it differ from the version I have in my hands? Does it matter?
Consider matters of identity in your design. What are the implicit differences between nodes, services, transactions? How can these differences be eliminated? How must different parts of your system remain in sync?