Investors have exchanges for lots of things, like stocks, currencies and commodities. They place buy and sell orders indicating what they want to exchange and at what price, and the exchange automatically executes a transaction whenever compatible buy and sell orders are outstanding. (I’m not an investing geek, so forgive me if this is somehow wrong.)
Why don’t we have a general exchange for every kind of good that can be bought and sold? Why should I have to search Google, Amazon, some price comparison site or Craigslist when I want something, often coming up empty-handed, when I could just place a buy order for it on a global exchange, and have the exchange find the optimal seller, if one exists, based on price, proximity, reputation, etc., transfer them my money, and tell them to mail me my item?
One might object that everyday goods aren’t like financial instruments. There’s an infinite number of kinds of goods, and the instances of one kind of good are going to differ from each other slightly or significantly in various ways that are of concern to the buyer. This is all true, but I don’t think it’s a barrier to automated trading. You’d just need an agreed-upon taxonomy of goods and an ontology for describing them. Then, buyers can state the type and minimum attributes of what they want and sellers can state the type and attributes of what they have. The exchange executes a transaction, optionally taking into consideration factors like how good the seller’s reputation is and how long it will take to ship.
Voila, Semantic Market.