1) Citation metrics have evolved over time from bibliometrics in the 1960s to more recent metrics like altmetrics and webometrics. They are used to assess the influence of published research.
2) Key citation metrics include the journal impact factor, h-index, and article-level metrics like citation counts and altmetrics. Data sources include Web of Science, Scopus, and Google Scholar.
3) Citation indexing links cited and citing articles, allowing researchers to trace the development of ideas over time. Citation analysis helps understand why authors cite other works.