deletions | additions       diff --git a/introduction.tex b/introduction.tex  index d8795e8..0f6ea8b 100644  --- a/introduction.tex  +++ b/introduction.tex 
...
Despite their sheer volume, the data collected in the context of large surveys represent only a portion of all the data generated in astronomy. Most discoveries rely upon smaller studies, and/or are based on heavily-processed subsets of many surveys. In any field of scientific endeavor, many different levels of data exist \cite{borgman}: from "raw" data to "processed" data, from "calibration" data to "published" data. If we imagine all data in astronomy to be a pyramid, data from large sky surveys occupies most of the bottom half of the pyramid: \textbf{primary data} from sky surveys are \textit{generic, raw and large}. But, as we just mentioned, these primary data are used by astronomers all over the world to produce more specific studies, where astronomers analyze and process primary data in many ways producing \textbf{derived data} which are \textit{specialized, processed, and small(er)}.  The physical and astronomical sciences have a well established reputation for being disciplines with a strong culture of data sharing. Astronomy has pioneered Open Access to both publications and data. In fact, the data generated by large sky surveys, such as those indicated above, are often  collected under national grants (e.g., NASA), government-sponsored grants,  archived by national government-sponsored  institutions (e.g., the Space Telescope Science Institute, STScI), NASA),  and made publicly available to anyone (e.g., at \url{http://archive.stsci.edu/}). The fact that astronomical data from large surveys are publicly available is remarkable, but by no means surprising. Astronomers collect data about the Universe, and thus, they feel a moral obligation to share collected data openly. Moreover, these data are collected under national programs that require data to be made openly available. Astronomers often have access to efficient and robust mechanisms that serve to archive, curate, and make primary data available (e.g. \url{http://archive.stsci.edu/}, \url{http://ned.ipac.caltech.edu/}, \url{http://skyview.gsfc.nasa.gov/}, \url{http://simbad.u-strasbg.fr/simbad/}). But, very few parallel systems exist for derived data, and none is yet robust. Because most, if not all, scientific articles in astronomy are based on derived data, making such data visible, intelligible and available to the public is of fundamental importance.