Metrical task systems (MTS) are abstract models for competitive analysis of online computation. Metrical task systems play roles in online problems such as paging, list accessing, and the k-server problem (in finite spaces). Metrical task systems were formulated by Borodin, Linial, and Saks.
In general terms, a metrical task system consists of a metric space with a metric and a transition table. These are used to represent all possible configurations.