Reference:

T. Honkela, S. Kaski, T. Kohonen, and K. Lagus. Self-organizing maps of very large document collections: Justification for the WEBSOM method. In I. Balderjahn, R. Mathar, and M. Schader, editors, Classification, Data Analysis, and Data Highways, pages 245–252. Springer, Berlin, 1998.

Suggested BibTeX entry:

@incollection{Honkela98klass,
    address = {Berlin},
    author = {T. Honkela and S. Kaski and T. Kohonen and K. Lagus},
    booktitle = {Classification, Data Analysis, and Data Highways},
    editor = {I. Balderjahn and R. Mathar and M. Schader},
    pages = {245-252},
    publisher = {Springer},
    title = {Self-Organizing Maps of Very Large Document Collections: Justification for the {WEBSOM} method},
    year = {1998},
}