This paper investigates the structure and dynamics of the Web 2.0
software ecosystem by analyzing empirical data on web service APIs and
mashups. Using network analysis tools to visualize the growth of the ecosystem
from December 2005 to 2007, we find that the APIs are organized into three
tiers, and that mashups are often formed by combining APIs across tiers. Plotting
the cumulative distribution of mashups to APIs reveals a power-law relationship,
although the tail is short compared to previously reported distributions
of book and movie sales. While this finding highlights the dominant role played
by the most popular APIs in the mashup ecosystem, additional evidence reveals
the importance of less popular APIs in weaving the ecosystem’s rich network
structure.