C1ExpressConnection component is also used for defining relations between tables. To open the Relations editor, select Edit Relations from the context menu or press the Relations property button.

To create a relation, select parent and child tables in corresponding combo boxes (if one or both of them are composite tables, you also need to select a constituent simple table in the "use fields of" combo box below). Then add one or more joins – equalities between a parent field and a child field.

Relations are used for two purposes master-detail relations and referential integrity (foreign key constraints).