In [13], the authors have proposed a gravitation based
model for information retrieval which they have derived
based upon Newton’s laws of gravitation. This model is used
in structured document retrieval and associates the attributes
of a document to three different terms: type, mass and
diameter. The model is peculiar in itself. On one hand, where
it uses rectangular shapes to represent documents that have
continuous values or hidden meanings of the terms in a
document, it uses spheres to represent discrete values or terms
that are explicitly used in it.