An edge definition is the definition of a path to follow to get from a starting object to one or more related objects. An edge definition can also include criteria to filter the objects across the specified relationships to only include a specific set.
Edge definitions have the following properties:
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A starting interface definition (required)
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A path definition that specifies the relationships to traverse from the starting interface definition along related interface definitions and the direction to traverse those relationships (required)
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Discrimination criteria that can be applied to objects at the end of the path (optional)
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Position criteria that can select a specific object from the set of objects that satisfy the discrimination criteria at the end of the path (optional)
Implicit Edges
Two implicit edge definitions exist for every relationship definition in the schema: one that is positive (going from end 1 to end 2 of the relationship), and one that is negative (going from end 2 to end 1). The following graphic shows the positive and negative relationship edges (+Rel1 and -Rel1) between object A and object B.
Explicit Edge Definitions
In addition to the automatically generated edge definitions (called implicit edges), you can explicitly define edge definitions for a variety of purposes in the Schema Editor. Explicit edge definitions can be used to traverse across multiple relationships, to select only certain objects from the destination end, or to do a combination of multiple relationship traversal and selective discrimination.
The following graphic shows an explicit edge definition that traverses multiple relationships by going from object A to object C through the relationship that each object has with object B. The path for this relationship is +Rel1, -Rel2.
Discrimination Criteria
Edge definitions can specify discrimination criteria, including position, to help you filter the objects at the end of the path defined by the edge definition. For example, you can use position criteria in an edge definition to return the fifth nozzle on a piece of equipment by specifying a numeric position of 5 when you define the edge definition. Another option is to specify that you want the first or last object in the path by defining named criteria for the edge definition. You can also use discrimination criteria based on property values to specify that you only want to see objects with a Process Case of Minimum by creating an edge definition whose discrimination criteria included ProcessCase = Min.
Another way to use discrimination criteria to filter results is to specify that all objects at the end of the path must support a particular interface. For example, if you want to create an edge definition to display the P&ID an object is on, you could specify that all objects at the end of the path must support IPIDDrawing to make sure that only P&IDs and not other objects that participate in the DwgRepresentationComposition relationship are returned by the edge definition.
The following UML diagram shows an edge definition that uses discrimination criteria to go from a piece of equipment to the P&ID on which the piece of equipment appears:
Edge Definitions in SmartPlant Foundation
In SmartPlant Foundation, edge definitions are custom relationship expansions that appear on the shortcut menu when a user right-clicks an object that exposes the relationship referenced by the edge definition. Instead of requiring the user to go directly from object A to object B in the tree view, an edge definition can be created to allow the user to traverse through multiple intermediate objects and display an object at the end of the relationship that meets specific criteria. For example, an edge definition could be created to expand to only the first nozzle on a vessel.
Without an edge definition, to get from object A to object D you would have to traverse from A to B, B to C, and then from C to D. With an edge definition, you could traverse directly from Object A to Object D.
System administrators might also create an edge definition to traverse directly from a plant to a unit. In SmartPlant Foundation, units are directly related to functional areas. However, a custom edge definition would allow the user to expand the plant to see the units without expanding a functional area first.
You can a set flag on the edge definition to determine whether all users have access to the edge definition. If the Filter out edge in display option is selected on the edge definition, then only those users in user groups that have been associated with the edge definition can see the edge definition in the SmartPlant Foundation client. Edge definitions show up in the relationships section of the shortcut menu for user groups that have access to the edge definitions.