Quantum categories. Quantization of the category of linear spaces

We define generalized bialgebras and Hopf algebras and on this basis we introduce quantum categories and quantum groupoids. The quantization of the category of linear (super)spaces is constructed. We establish a criterion for the classical value of the dimension of the polynomial function algebra on the full subcategory of this quantum category specified by Sudbery type commutation relations for quantum vector spaces (the ``Poincare -- Birkhoff -- Witt property''). The criterion is the equality of the ``quantum constants'' $c_\a=c_\b^{\pm 1}$ of the quantum vector spaces. (These constants appeared in earlier works on PBW for the multiparameter quantization of the general linear group.) Links with the Yang-Baxter equation and the Yang -- Baxter structures of quantum linear spaces are established. The role of categories as a generalization of groups is discussed.