Centralized Search vs Decentralized Search

Developing a Grid-Based Search and Categorization Tool
http://library.cern.ch/HEPLW/8/papers/1/

In class we use the phrase "decentralized search," but we never discussed a definition, and we never seem to use the phrase "centralized search." What do these mean and how do they relate to each other?

From the introduction: "Today's search engines are extremely centralized. In order to index a document it must be downloaded, processed and its index stored - all in one central location." It sounds like the Binary Search that Professor Hartline discussed during Math Corner is a centralized search. We started with a sorted list of numbers and then we found a random number in that list. Each item in the list was already downloaded, processed, and indexed.

It seems like the goal of this search engine is to search for information within a grid system, like the network models we saw in class. Instead of traversing a sorted list, it jumps from node to node within a network until if finds what it's looking for.