## Abstract

Consider a directed graph (digraph) in which vertices are assigned color sets, and two vertices are connected if and only if they share at least one color and the tail vertex has a strictly smaller color set than the head. We seek to determine the smallest possible size of the union of the color sets that allows for such a digraph representation. To address this problem, we introduce the new notion of a directed intersection representation of a digraph, and show that it is well-defined for all directed acyclic graphs (DAGs). We then proceed to introduce the directed intersection number (DIN), the smallest number of colors needed to represent a DAG. Our main results are upper bounds on the DIN of DAGs based on what we call the longest terminal path decomposition of the vertex set, and constructive lower bounds.

Original language | English |
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Article number | 9236641 |

Pages (from-to) | 347-357 |

Number of pages | 11 |

Journal | IEEE Transactions on Information Theory |

Volume | 67 |

Issue number | 1 |

DOIs | |

Publication status | Published - Jan 2021 |

Externally published | Yes |

## Keywords

- Directed intersection number
- directed acyclic graph
- intersection representation