 Directed acyclic graphs may also be used as a compact representation of a collection of sequences . In this type of application , one finds a DAG in which the paths form the given sequences . When many of the sequences share the same <unk> , these shared <unk> can be represented by a shared part of the DAG , allowing the representation to use less space than it would take to list out all of the sequences separately . For example , the directed acyclic word graph is a data structure in computer science formed by a directed acyclic graph with a single source and with edges labeled by letters or symbols ; the paths from the source to the sinks in this graph represent a set of strings , such as English words . Any set of sequences can be represented as paths in a tree , by forming a tree vertex for every prefix of a sequence and making the parent of one of these vertices represent the sequence with one fewer element ; the tree formed in this way for a set of strings is called a <unk> . A directed acyclic word graph saves space over a <unk> by allowing paths to <unk> and rejoin , so that a set of words with the same possible <unk> can be represented by a single tree vertex . 
