Abstract
We propose two new tools to address the evolution of hyperlinked corpora. First, we define time graphs to extend the traditional notion of an evolving directed graph, capturing link creation as a point phenomenon in time. Second, we develop definitions and algorithms for time-dense community tracking, to crystallize the notion of community evolution. We develop these tools in the context of Blogspace, the space of weblogs (or blogs). Our study involves approximately 750 K links among 25 K blogs. We create a time graph on these blogs by an automatic analysis of their internal time stamps. We then study the evolution of connected component structure and microscopic community structure in this time graph. We show that Blogspace underwent a transition behavior around the end of 2001, and has been rapidly expanding, not just in metrics of scale but also in metrics of community structure and connectedness. By randomizing link destinations in Blogspace, but retaining sources and timestamps, we introduce a concept of randomized Blogspace. Herein, we observe similar evolution of a giant component, but no corresponding increase in community structure. Having demonstrated the formation of micro-communities over time, we then turn to the ongoing activity within active communities. We extend recent work of Kleinberg (2002) to discover dense periods of "bursty" intra-community link creation. Furthermore, we find that the blogs that give rise to these communities are significantly more enduring than an average blog. © 2005 Springer Science + Business Media, Inc.