The paper presents some topics related to an automatic approach to the generation of symbolic kinematic models of robot mechanisms. The approach applies to direct and inverse kinematics, also in the cases of multiple arms, and can be applied to robot mechanisms made up of drivers and single-loop determined kinematic chains (SLDCs). A robot mechanism is modeled as a hierarchy of such subchains, which form a set of independent kinematic loops. The paper describes the algorithm that recognizes and organizes, in a hierarchical way, all SLDCs of a robot mechanism. Consistent definitions for the entities involved in the modeling steps are given. The algorithm computes the kinematic constraints between all couples of links in the robot mechanism in order to provide mobility information (e.g., dependencies on drivers, types and geometric properties of the relative displacements).