Some intros to NoSQL databases

In general, I am a bit late for the whole NoSQL party, but nevertheless here are some interesting articles:

• A gentle introduction to CouchDB for relational practitioners
• Immutability, MVCC, and garbage collection
• Accountants Don't Use Erasers

Mahout

A nice intro slideset to Mahout, a mapreduce enabled hadoop machine learning library in java:

Introduction to Mahout and Machine Learning from Varad Meru

Market Makers & Prediction Markets

A while ago I posted on the idea of futarchy and followed up with a post on implementation and issues of virtual stock markets.

I only posted links on auction markets, i.e. where one party makes an offer, another one a request and the system finds a match. That only works good for systems with high liquidity. Especially on prediction markets with combinatorical outcomes (e.g. of the form "if person A becomes the candidate for party 1, then party 2 will win the election" or even more complex constructions) this is difficult: you need to find people making similar opposite bets to match. A way around of this is to use a market maker instead of an auctioneer. It takes the trades directly instead of leading a negotiation between to parties. The price is set automatically by the system. This, of course, also has drawbacks. In a real life system, the market maker provides liquidity and thus is at risk losing some money. Moreover, the pricing of the goods depends on parameters of the market maker. Wrong values for thick or thin (i.e. markets with many/few participants) might make the price either bounce up and down or move only tiny bits.

• On combinatorial prediction markets
• an aricle on implementing a simple market maker
• article on books and market makers
• Multi-Outcome markets

On (implementation issues of) Virtual Stock Markets

After my recent post on prediction markets, I decided to implement a small auctioneer for virtual stock markets with two parties making deals, i.e. not a market maker mechanism but a (traditional) double auction. But, despite the simple idea behind a bid/ask driven market, the implementation has to take into account quite a number of details: can you buy/sell one unit or multiple units of a good at a time? Does trading occur at discrete events or is it continuous? Is pricing uniform (all trade at the same equilibirum price) or discriminatory (individual matching of bid/ask orders)? And, if one the two options is chosen, how is the price determined?

• Beside the double auction system, bidding can take other forms: Auctions and Bidding: A Guide for Computer Scientists
• Everything you wanted to know about double auctions, but were afraid to (bid or) ask
• And finally a paper on two multi unit k-double auction algorithms