To select a relationship or role, you must click with the mouse in or near one of its selection areas. For relationships, the selection area is at the meeting point of the role lines, and is either the graphical symbol or label text for the relationship, or a red dot if there is no symbol. For roles, the selection area is the role line and possible symbol at the end of it. When a relationship is selected it displays selection handles around its symbol, or a single selection handle if it has no symbol. When a role is selected it displays a selection handle at both ends of its line, and also for any breakpoints along the line.

To select multiple relationships or roles, select the first element by clicking it with the left mouse button, then holding Ctrl down while you click each of the other elements. Alternatively, you can select all design elements in an area by clicking and dragging with the left mouse button to define the area you want to select.

To select all elements in the drawing area (i.e. all objects, relationships and roles), select Edit | Select All or use the shortcut key Ctrl+A.

Relationships are connections between objects. In the Diagram Editor these are represented as the meeting point of role lines, possibly with an associated symbol. Relationships can be viewed and edited similarly to objects. To edit the properties of a relationship:

To add a new binary relationship (i.e. a relationship between two objects):

As a result a dialog window opens with possible relationships to be added. Each item is a binding, consisting of a relationship, the roles that will be created with the relationship, and which object will be in which role. Selecting an item will show a preview of the selected binding in the drawing area. Depending on your preference settings for relationship creation (Section 3.1.3), the order in which you select objects may affect the choices and assignment of roles to objects. If only one combination of relationships and roles is possible the tool bypasses this dialog and the property dialog appears immediately. This dialog contains tabs for property dialogs on the relationship and each of the roles.

Alternatively, you can also create a binary relationship as in previous versions of MetaEdit+. Selecting the first object, and choose Connect... from its pop-up menu. As you move the cursor to another object, a line will follow it from the first object. Press the left mouse button over the second object, and fill in the property dialogs as above.

To create an n-ary relationship (i.e. a relationship involving more than two objects):

It is also possible to skip step 1, by placing the relationship first. The role to the first object should then be drawn as the first role in step 3.

N-ary relationships can also be created as in previous versions of MetaEdit+: first select all the objects that you want in the relationship (e.g. by Ctrl-clicking them) and then select Connect... from the pop-up menu. You must then click in the drawing area to fix the position of the relationship, where any relationship symbol will appear.

The type toolbar provides two useful options for easing the creation of relationships in certain situations. The first such option is the generic relationship button (as shown in Figure 4–3) that initiates the creation of any relationship type. The type for the created relationship is determined from context, or the user is prompted to choose between legal relationship types in that context when the creation is confirmed.

The other option is the sticky mode for relationship creation, which can be enabled by holding down the Ctrl key when selecting the relationship type. This enables the user to create several relationships of the same type sequentially, without needing to re-select the relationship type after each one is created. The sticky mode is retained until a new type is selected or the right mouse button is pressed to cancel the creation of a relationship. Sticky mode applies also to the generic relationship creation.

As with objects, relationships can be moved. To do this:

The relationship symbol can be moved to the midpoint between its objects, and all existing break points in all roles of the relationship can be removed by selecting Straighten Relationship (or Straighten Relationship(s) if you have selected multiple relationships) from the pop-up menu of the relationship. Normally, this will not affect the target points of roles, but if Shift is held down it will also reset the target points.

It is also possible to move straight binary relationships so that their straightness is preserved, i.e. the target points at the end of both roles are also moved in relation to the position of the relationship (as in Figure 4–14). This can be done by holding down the Ctrl and Shift keys while moving the relationship.

Scaling relationship symbols and aligning them to the grid is described at the end of Section 4.1.6.

Relationships are connected to objects through roles. Each relationship has at least two roles and they too can have properties. An example of a property for a role is a cardinality constraint in an Entity-Relationship-Attribute Diagram.

Because roles are attached to relationships their management is closely related to the management of relationships. When a relationship is created, you are also asked for values for its roles, and when a relationship is removed the roles too are removed.

Property dialogs for roles can be accessed as with relationships. To edit role properties:

Roles consist of a line, possibly with breakpoints along the line, and a target point at the end of the line where the role connects to the object (Figure 4–15). Normally the breakpoints and target point move together with the relationship and objects, but it is also possible to move them separately.

For target points, it is important to understand that they do not lock the end of the role line at a certain fixed point in the drawing area. Rather, role lines aim at target points, which are specified as offsets from the centre of the object’s connectable. This means while moving or scaling an object with roles that have specified target points, the role lines stay aimed at those target points, but do not necessarily stop at the target point. Role lines are always drawn to stop where they cut the object’s connectable. If a line aimed at the target point will not cut the object connectable, the target point is ignored and the line is retargeted to the closest point on the connectable.

To add a new breakpoint to an existing role line:

You can remove a breakpoint either by control-clicking it or by choosing Delete Point from its pop-up menu. All existing break points in all roles of a relationship can be removed by selecting Straighten Role from the pop-up menu of the relationship. Normally, this will not affect the target point, but if Shift is held down it will also reset the target point.

To move the target points, drag them along the symbol perimeter (as in the lower part of Figure 4–15). If the current selection includes multiple roles, dragging one role’s target point drags the target points of all selected roles attached to that object — useful in Sequence Diagrams. To restore a target point into its original position, control-click it or select Restore Target Point from its pop-up menu.

You can add a new role to the relationship by selecting it and choosing Add a New Role... from its pop-up menu. An alternative way to add a role is to activate the respective relationship creation from the type toolbar, then click left mouse button on the relationship you want add a role to (the relationship must be of the same type as selected in the toolbar) and then drag the role line on the target object.

Roles can be deleted either by pressing the Delete key when the role is selected, by choosing Delete from the pop-up menu or toolbar or by selecting Edit | Delete. Note that if the relationship will be left with fewer than two roles the relationship is removed as well.

It is also possible to reconnect a role from one object to another, or to a different port. To do this, select the role then hold down Shift and drag its target point handle from the current object to the new object or port. Alternatively, you can select Reconnect from the role’s target point’s pop-up menu. Unlike the Shift-drag method, selecting Reconnect from the menu will also discard any existing breakpoints along that role line; to keep them, hold down Shift when selecting from the menu. You can cancel the reconnect in either method by right-clicking.

If reconnecting was not possible with the original role, but a role of a different type would work, MetaEdit+ will prompt you to select that type.

To delete a relationship, either press the Delete key when the relationship is selected, choose Delete from the relationship’s pop-up menu or toolbar, or select Edit | Delete. When a relationship is deleted its roles are also deleted.