In OData, a navigation property is a property on an entity that is itself either a single entity or list of entities.
A single-entity navigation property signifies a one-to-one relationship; for example, an OData service might allow a Product to have only one Category. In this service, Category might be a navigation property on Products.
An entity set navigation property signifies a one-to-many relationship; for example, many Products can belong in the same Category. In this service, Products might be a navigation property on Categories.
Working with Navigation Properties Relationally
Navigation properties in OData link related entities. Similarly, in a relational database, a foreign key serves to link tables. For example, a Product record might have a CategoryId column, which uniquely identifies what Category the Product belongs to. However, there is no requirement in OData that an entity must contain a foreign key reference to a related entity. This means sometimes you will get navigation properties without having a foreign key reference to that entity on the parent or back to the parent from the related entity. In cases without a foreign key reference, the navigation property's existence is the only thing that can be used to identify a relationship between the two entities.
NavigationPropertiesAsViews is useful for accessing data in OData services that lack foreign key references. Likewise, it can be used to retrieve related entites that do not exist by themselves such as LineItems on an Invoice. See Views for more information on querying navigation properties.
The driver supports OData deep inserts. See Tables for more information on specifying navigation properties when you create an entity.