From the webpage:
The VLTS acronym stands for “Very Large Transition Systems“.
The VLTS benchmark suite is a collection of Labelled Transition Systems (hereafter called benchmarks).
Each Labelled Transition System is a directed, connected graph, whose vertices are called states and whose edges are called transitions. There is one distinguished vertex called the initial state. Each transition is labelled by a character string called action or label. There is one distinguished label noted “i” that is used for so-called invisible transitions (also known as hidden transitions or tau-transitions).
The VLTS benchmarks have been obtained from various case studies about the modelling of communication protocols and concurrent systems. Many of these case studies correspond to real life, industrial systems.
If you aren’t already working with large graphs in your work on topic maps, you will be.