View relations (ViewRelation objects) are depicted in a data set diagram with arrows connecting nodes - table views. View relations are optional; it is possible to have a data set without them. View relations play the following roles:

• They define the master-detail (parent-child) hierarchy between table views. When you use a data set with view relations as the DataSource for data bound controls, you can bind one grid to a master (parent) table view and another grid to a detail (child) table view. Then the detail grid will show the child rows related to the parent row that is current in the master grid at the moment. See also, How to Access Table View Data.
• They allow programmatic access to parent and child rows of a table view row, using methods GetParentRow and GetChildRows. Note that even without view relations; it is possible to navigate from parent to child rows and vice versa between tables, for table rows, using the same C1DataRow methods GetParentRow /GetChildRows and relations between tables. For more information, see Simple Relations and Composite Relations.

A view relation between table views is usually based on the relation (Relation object) between the two tables represented by those two table views (except for custom view relations, see Custom View Relations). This relation can be simple or composite (see Simple Relations and Composite Relations). It is determined by the ViewRelation.Relation property. A view relation, as an arc in the data set diagram, can have direction opposite to the direction of the table relation on which it is based. For example, having a one-to-many relation Customers – Orders, we can create a many-to-one view relation Orders – Customers, based on Customers – Orders, but in inverse order (direction). So, if the Relation object Customers – Orders has Parent = Customers, Child = Orders, the view relation, if inverted, will have Parent = Orders, Child = Customers. This inversion does not change the original Relation object. Usual practice is to define all simple relations, Relation objects shown in the Relations window as one-to-many, and then apply them in diagrams, create view relations based on them, in direct (one-to-many) or inverse (many-to-one) order. To invert a view relation, right-click the relation in the diagram and select Invert from the context menu that appears.