Relationships.er

/*
 dbdia example - relationship definition examples
 Eduardo Marques
 https://github.com/edrdo/dbdia
*/

EntityA ( ) // with no attributes (just for convenience)
EntityB ( ) // you can in any case ommit attributes in diagrams
EntityC ( ) // using the 'rel' diagram type generation

// Relationship: Rel1 
// Entities involved: EntityA and EntityB
// Cardinality: 1 to N
// Participation: partial for EntityA, total for EntityB
// Relationship attributes: none

EntityA --- 1 --- < Rel1 > === N === EntityB

// Relationship: Rel2
// Entities involved: EntityA and EntityB
// Cardinality: M to N
// Participation: partial for both entities
// Relationship attributes: none

EntityA --- M --- < Rel2 > --- N --- EntityB

// Relationship: Rel3
// Entities involved: EntityA and EntityC
// Cardinality: 1 to 1
// Participation: total for EntityA, partial for EntityC
// Relationship attributes: Rattr1, { RAttr2 } as shown.

EntityA === 1 === < Rel3( RAttr1, { RAttr2 } )> --- 1 --- EntityC