3 Jun 2002 raph   » (Master)


Review of Linked: The New Science of Networks, by Albert-László Barabási, ISBN 0738206679.

Highly recommended. Over the past few years, there has been a flowering of academic research into the nature of networks such as the link structure of the World Wide Web and social networks. This book collects some of the highlights of this research, and presents them as well-written stories. Barabási makes a strong case that network thinking will have profound implications over the coming years, not just for the World Wide Web, but for biology, social networks, and other areas of science as well.

"Scale-free" networks have a central place in the book, not surprising as Barabási is co-author of a groundbreaking paper on the subject. The original paper dealt with the Web, but subsequent research has turned up a number of other networks with similar topology. Even within the Internet, scale-free topology applies both to the network of routers and backbones as well as the link structure of the Web.

Scale-free networks are instantly recognized by their characteristic power-law degree distribution. There are a few highly-connected nodes, and many nodes with just one or two links. By contrast, the degree distribution in random networks tends to be a tightly clustered bell curve.

A simple model generates randomized scale-free networks. Start with a small seed network, possibly a single node. For each new node, add a link from that node to existing nodes, with probability proportional to the indegree of the existing node. Thus, the model captures both growth and preferential attachment. If either element is missing, the resulting network is not scale-free.

These networks have a few important properties. First, their diameter is very small. This property has been known in social network theory since the brilliant "small world" experiments of Milgram in 1967. The idea was popularized in the 1990 play by John Guare, "Six Degrees of Separation", and has since entered the popular vocabulary.

Second, such a network stays well connected even when random nodes are removed. This is an "attack resistance" property of the network, not directly related to the attack resistance of trust metrics, my own specialty (although the underly concept of network flow plays an important role in the analysis of both).

However, when a few highly connected nodes are removed, the network fragments. Thus, scale-free networks are in this way more vulnerable than random networks.

Barabási does not address trust metrics. This is a bit surprising, because Google plays a part in the book, as a "more fit" search engine that rapidly becomes a hub even though existing search engines such as Inktomi and Altavista have already established names for themselves. Barabási misses the opportunity to explain why Google is better. Also, Gaure's play deals with a con artist who is expert at playing his social network to further his own goals, but Barabási does not pursue the theme of trust (and violation of that trust) in social networks.

Even if you are familiar with scale-free network theory, the book is still a fun read, and the presentation may be helpful in talking with others. For people involved in Internet software design, and in design of p2p networks, this book is essential reading. The book nicely balances an accessible presentation with meaty intellectual content. Most people who enjoy thinking about the world will find something of interest.

Thanks to Jim McCoy for recommending this book to me.

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