• Timeliness period: is the time range between the release date of a library version $v$ and the most recently released version of its library ordered by time, which is not necessarily it next version
    • $v$ is timely if $tim(v) = 1$: $v$ was a success during its timeliness period and users relied on it
    • $v$ is over-timely if $tim(v) > 1$: $v$ has attracted users beyond its timeliness period
    • $v$ is under-timely if $tim(v) < 1$: users relied on older versions during its timeliness period