document: On the bursty evolution of blogspace 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 750K links among 25K 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 over the past year , not just in metrics of scale , but also in metrics of community structure and connectedness . This expansion shows no sign of abating , although measures of connectedness must plateau within two years . 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 ( 11 ) to discover dense periods of `` bursty '' intra-community link creation .
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