1. A driver assistance system for a motor vehicle, comprising: a sensor device for measuring data about an environment of the vehicle; at least two assistance functions dependent on the measured data; and a data processing device, which analyzes the measured data and generates at least one specific environmental hypothesis for each assistance function, which provides output data in a form prepared for the corresponding assistance function, wherein at least one environmental hypothesis which has a structure divided into a plurality of partial hypotheses is predefined in the data processing device, the partial hypotheses having a logical relationship with one another such that output data of one partial hypothesis flow into the generation of another partial hypothesis, and at least two assistance functions directly or indirectly use a shared partial hypothesis, wherein the at least one environmental hypothesis determines how the measured data is interpreted, wherein each of the partial hypotheses represents a term described by an aspect of the environment, wherein the logical relationship between partial hypotheses includes at least one of a subset relation and an implicit relation, and wherein a warning about leaving a lane is provided as an additional assistance function, wherein an additional sensor provides data which is analyzed according to a second environmental hypothesis, which has an interconnected structure having a plurality of partial hypotheses, wherein the plurality of partial hypotheses is as follows: (a) the sensor has detected at least one object, and for a plurality of objects, a corresponding plurality of copies of the first partial hypothesis is generated; (b) the object is a spatial object extending in the vertical direction; (c) the object is a flat object that defines a left boundary and a right boundary of the lane; (d) the spatial object which was detected in (b) is within the lane; and (e) the vehicle is about to cross a lane boundary; wherein for the second environmental hypothesis, efficient data processing is achieved by partial hypotheses (b) and (c) jointly using the results of partial hypothesis (a), and wherein for partial hypothesis (d), the results of partial hypotheses (b) and (c) are combined.