A bowing is a sequence of bow motions that enable a piece of music to be played on a string instrument with an appropriate interpretation and sound. Traditional notation shows only the bow direction for a few notes. We propose a bowing model, which contains information about the bowings of all the notes, and we show how the bowing model can be represented in software and describe how algorithms can use it to perform several tasks that help the performer. The model, and the algorithms, are suitable both for offline editing of music and for presentation on an electronic display during performance. In particular, software can show or hide bowings on various notes, according to the performer's needs; it can calculate a full bowing; it can modify a bowing based on preferences indicated by the performer; and it can allow bowings to be archived and searched. This approach is not prescriptive: the performer is in full control of all artistic decisions, while the software carries out repetitive tasks