Using PowerPivot in Excel 2013 - Business Intelligence in Microsoft SharePoint 2013 - page 110

FIGURE 4-16 The Relationships button on the Data tab.
Note The Relationships button is disabled if there is no Data Model or if the Data Model
has only one table (to create relationships, you need at least two tables).
In the Manage Relationships dialog box that opens (see Figure 4-17), click the New button. The
Create Relationships dialog box opens, as shown in Figure 4-18.
FIGURE 4-17 The Data Model Manage Relationships dialog box.
FIGURE 4-18 The Data Model Create Relationship dialog box.