Draft:Multiplicative graph

  • Comment: This may be a notable topic, but the article provides almost no background for readers who aren't versed in the topic. Please provide a general introduction as a lead section. WeirdNAnnoyed (talk) 22:08, 8 August 2026 (UTC)


For comparison, this diagram shows a typical arrow composition in an ordinary category. (Without arrow composition, it is simply a directed graph.) The arrows and in the diagram are consecutive; they connect in In an ordinary category, the composition of any pair of consecutive arrows exists, whereas in a multiplicative graph, a pair of consecutive arrows is not necessarily composable.[1]

In mathematics, a multiplicative graph (in French:graphe multiplicatif or neocategory[2] in some English-language papers) is an algebraic structure in category theory. It is a generalization of an ordinary category in the sense that neither the associativity of arrow composition nor the composibility of a pair of connected arrows are assumed. While an ordinary category is a notion combining a directed graph and a monoidal structure, a multiplicative graph is a partial magma-like structure. Namely, it is a structure in one‑to‑one correspondence with the nodes of a directed graph, and is equipped with partial law of composition that satisfies only left and right identities.[2]

Arrow composition in an ordinary category satisfies the following property: if arrows and connect in the sense that their composition is defined, and, moreover, and In a multiplicative graph, however, condition does not guarantee the existence of within that structure without further assumptions – but if this composition exists, it also satisfies and [3] When drawing a diagram for a multiplicative graph, it is almost always necessary to explicitly draw all existing arrows that play a role in the argument. For example, as shown in Coppey (1980), square diagrams in a multiplicative graph can take one of five types depending on which potential compositions in the diagram are actually defined.[4]

This notion first appears in Ehresmann's book Catégories et structures.[5] The French school bases its definition of sketch on the notion of a multiplicative graph,[6] because this definition required a category-like structure that avoided redundant axioms as much as possible.[7] This structure is the multiplicative graph, and this is a type of relaxed notion of category, such as a semicategory.[8]

Cury is studying enriched multiplicative graph.[9] As a more general notion, there is the compositional graph, and multiplicative graphs can be seen as strongly identitive compositional graphs.[8]

Definition

Group-like structures
Total Associative Identity Divisible
Partial magma Unneeded Unneeded Unneeded Unneeded
Semigroupoid Unneeded Required Unneeded Unneeded
Small category Unneeded Required Required Unneeded
Groupoid Unneeded Required Required Required
Magma Required Unneeded Unneeded Unneeded
Quasigroup Required Unneeded Unneeded Required
Unital magma Required Unneeded Required Unneeded
Loop Required Unneeded Required Required
Semigroup Required Required Unneeded Unneeded
Associative quasigroup Required Required Unneeded Required
Monoid Required Required Required Unneeded
Group Required Required Required Required

A multiplicative graph is couple formed by a set denoted by , and a partial law of composition on satisfying the following axioms:[2][10]

  1. is a mapping from a subset of (denoted by and called the set of composable couples) into ; instead of , we write and we call the composite of .
  2. There exists a reflexive graph[6] (i.e. and are retractions from onto a subset of , denoted by ), such that:
(existence of units[11][12]): For each element of , the composites and are defined, and we have
Here, is the right identity of and is called the source of , while is the left identity of and is called the target of ;
(coherence of dom/cod[12][13]): If the composite is defined, then:

From the condition 2, the reflexive graph is uniquely defined.

Example

  • An ordinary category is a multiplicative graph in which all the couples where are composable (so that is the pullback of ), the law of composition being furthermore associative.[2][12][14]
  • For the two axioms above, a notion got by adding only the associativity axiom to a multiplicative graph, that is, a notion that an ordinary category without the composibility axiom, this is called a precategory.[12] But, this is not standard terminology, a precategory is usually synonymous with a semigroupoid and does not require each object to have an identity morphism.

See also

Notes

  1. ^ Cury 2004
  2. ^ a b c d Bastiani & Ehresmann 1972, §1. Neocategories and neofunctors.
  3. ^ Coppey 1980, Introduction.
  4. ^ Coppey 1980, 2. Produits tensoriels (unitaires) et fermetures.
  5. ^ Ehresmann 1965, ch. I, Dèfinition 8.
  6. ^ a b Wells 2009, 11.3 Compositive graphs
  7. ^ Cury 2004, INTRODUCTION
  8. ^ a b Mateus, Sernadas & Sernadas 1999
  9. ^ Cury 1979
  10. ^ Ehresmann 1965, ch. I, §.B) Graphes multiplicatifs et catègories. For the definition of "classe multiplicative", see ch. I, § A) Classes multiplicatives.
  11. ^ Ehresmann 1965, ch. I, Dèfinition 8. (G1)
  12. ^ a b c d Coppey 1980, 1. Graphes multiplicatifs, foncteurs, transformations naturelles.
  13. ^ Ehresmann 1965, ch. I, Dèfinition 8. (G2)
  14. ^ Ehresmann 1965, ch. I, Dèfinition 11.

References

  • Bastiani, Andrée; Ehresmann, Charles (1972). "Categories of sketched structures" (PDF). Cahiers de Topologie et Géométrie Différentielle Catégoriques. 13 (2). ISSN 1245-530X.
  • Coppey, L. (1980). "Quelques problèmes typiques concernant les graphes multiplicatifs" (PDF). Diagrammes (in French). 3 (2). ISSN 0224-3911.
  • Coppey, L. (1990). "Actes des journées E.L.I.T. (Univ. Paris 7. 27 juin-2 juillet 1988)" (PDF). Diagrammes (in French). 24: 33–76.
  • Coppey, L.; Lair, C. (1984). "Leçons de théorie des esquisses" (PDF). Diagrammes (in French). 12 (4). ISSN 0224-3911.
  • Cury, F. (1978). Graphes multiplicatifs enrichis (Thesis) (in French).
  • Cury, F. (1979). "Systèmes de générateurs et relations pour les catégories enrichies" (PDF). Diagrammes (in French). 1.
  • Ehresmann, Charles (1965). Catégories et structures (in French).
  • Ehresmann, Charles (1969). "Construction de structures libres". Category Theory, Homology Theory and their Applications II. Lecture Notes in Mathematics (in French). Vol. 92. pp. 74–104. doi:10.1007/BFb0080766. ISBN 978-3-540-04611-0.
  • Mateus, Paulo; Sernadas, Amílcar; Sernadas, Cristina (1999). "Precategories for Combining Probabilistic Automata". Electronic Notes in Theoretical Computer Science. 29: 169–186. doi:10.1016/S1571-0661(05)80315-9.

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