In UML modeling, a connector is a line in a diagram that represents a relationship in a model. Connectors show all or part of the semantics of their underlying relationships; however, connectors do not add any semantic information to the model.
Connectors are graphic representations of their respective relationships. You place connectors in diagrams to join diagram elements that represent model elements with a relationship.
You view relationships in the Model Explorer view and connectors in the diagram editor. You can only add relationships to a model by inserting connectors in a diagram; you cannot add relationships in the Model Explorer view. A connector represents only one relationship, and each relationship is usually represented by one connector. However, a relationship can also be represented by multiple instances of a connector or none at all in one or more diagrams.
Each connector has properties that govern its appearance in the diagram editor. The properties for a specific connector do not affect its underlying relationship or any other connectors that represent that relationship.
In addition, each connector has the same properties as its underlying relationship. Changing the value of one of these properties affects both the connector and its underlying relationship. For example, if you modify the Name property, the modification is updated in the relationship and all of the connectors that represent it, whether the name is modified in the Model Explorer view, the Properties view, or the diagram editor.