The information theory and the collapse of a wavefunction at the measurement of a spin 1/2 projection

From the point of view of the information theory, a model of the collapse phenomena at the measurement of a spin 1/2 projection is developed. This model phenomenologically includes an observer. The model allows not only to determine the state of a system after the measurement but also to compute the state of the observer. The state of the observer is equivalent to the operator of a spin projection which the observer will measure at the next measurement.