In recent years, the so called "Bag of Words" (BoW) representation has drastically grown
in importance in the Pattern Recognition research area: in such representation, the object
is characterized by the repetition of basic, "constituting" elements called words. By
assuming that all possible words are stored in a dictionary, the bag of words vector for
one particular object is obtained by counting the number of times each element of the
dictionary occurs in the object. This paradigm has been introduced in the text processing
community, where all its ingredients have a clear semantic meaning (words, documents,
dictionary). After that, it has been exported to an impressively large set of scenarios
becoming a standard reference representation.
In some cases, however, its usage has been extended too far, having been applied "as it
is" in situations where not all the concepts/tools of this paradigm have a meaningful role.
For example, there are many scenarios where it is impossible to define natural
words/dictionaries, or where such definitions fail in properly capturing all the facets of the
data. In other cases, the straightforward application of the bag of words paradigm is too
simple to capture the complexity of the problem, or can spoil all the information
contained in the data.
Against this background, in this project we aim at critically review and analyse the bag of
words representation paradigm, describing possible structural failures and proposing
We will pay particular attention to the fundamental assumptions and definitions of such
paradigm (like definition of words, the counting procedure, the definition of dictionary);
moreover, significant efforts will be devoted to the formal management of the
uncertainty, which models the fact that some words could be more expressive, or general
than others, deserving novel BoW modelling methodologies, absent so far in the