Geometric network connectivity rules(ArcInfo and ArcEditor only)
Release 9.2 Last modified February 1, 2008	Print all topics in : "Creating and managing geometric networks"

About geometric network connectivity rules

NOTE: Although geometric networks can be both created and edited in ArcInfo and ArcEditor, they are read-only in ArcView.

In most networks, you don't want all edge types to be able to logically connect to all junction types. Similarly, not all edge types can logically connect to all other edge types through all junction types. For example, in a water network, a hydrant can connect to a hydrant lateral but not to a service lateral. Similarly, in the same water network, a 10-inch transmission main can only connect to an 8-inch transmission main through a reducer.

Network connectivity rules constrain the type of network features that may be connected to one another and the number of features of any particular type that can be connected to features of another type. By establishing these rules along with other rules, such as attribute domains, you can maintain the integrity of the network data in the database. At any time, you can selectively validate features in the database and generate reports as to which features in the network are invalid—that is, are violating one of the connectivity or other rules.
Learn more about attribute domains

Types of connectivity rules

There are two types of connectivity rules: edge-junction rules and edge-edge rules. An edge–junction rule is a connectivity rule that establishes that an edge of type A may connect to a junction of type B. An edge–edge rule is a connectivity rule that establishes that an edge of type A may connect to an edge of type B through a set of junctions. Edge–edge rules always involve a set of junctions.

You can establish and modify the connectivity rules for a network from within ArcCatalog by modifying the geometric network properties. You can establish connectivity rules between two feature classes, a feature class and the subtype of another feature class, or between a subtype of one feature class and the subtype of another. In the water network example described above, a connectivity rule would be established between two subtypes of the same edge feature class and a subtype of a third junction feature class (10-inch and 8-inch transmission mains and reducer valves).

Network connectivity rules describes how to establish an edge–junction rule and edge–edge rule. For simplicity, each is done separately, but any number of rules can be established or modified for the network at a single time.

Default junctions

Both edge–edge and edge–junction connectivity rules can have default junctions associated with them. While default junctions are optional with edge–junction connectivity rules; they are required by edge–edge connectivity rules. Default junctions are automatically inserted by ArcMap when creating connectivity and new features in a network. If the business rules that drive the creation of connectivity rules  do not have a  clear default junction class or type, setting the default junction class to be the Orphan junction feature class is a valid solution.

When an edge pair has an edge–edge connectivity rule defined in the database, and you create a new edge that connects to an existing edge, the default junction is automatically inserted. For an edge–junction connectivity rule, ArcMap automatically inserts the default junction at the free end of new edges that are created in the network.

About establishing connectivity rules

Connectivity rules are established and modified using the geometric network's Properties dialog box in ArcCatalog.

The two examples given here describe how to establish an edge–junction rule and an edge–edge rule. For simplicity, each is done separately, but any number of rules can be established or modified for the network at a single time.

How to establish connectivity rules (ArcInfo and ArcEditor only)

Adding an edge-edge rule in ArcCatalog

1. Right-click the geometric network.
   
2. Click Properties.
   
3. Click the Connectivity tab.
   
4. Click the drop-down arrow and click the feature class for which you want to create a rule.
   
5. Click the subtype of the feature class if your feature class has subtypes.
   
6. Navigate to and check the edge feature class or subtype you want to make connectable to this edge subtype or feature class and check it.
   
7. Browse for and check the junction feature classes and subtypes through which these edge feature classes or subtypes will be permitted to connect.
   
8. The first junction feature class and\or subtype selected for the edge-edge rule will automatically be set as the default junction for the rule. If you want to set a different default junction type, right-click the junction subtype or feature class in the Junction subtypes list, then click Set as default. Only one default junction is allowed per edge-edge rule.
   
9. Click OK or Apply to create the rule in the database.
   

Tips

If an edge–junction rule doesn't already exist between one of the edge subtypes or feature classes and one of the junction subtypes or feature classes, a rule is automatically created. To set a default junction type, right-click the junction subtype or feature class in the Junction subtypes list, then click Set as default. Setting the default junction class to be the Orphan junction feature class is a valid solution if your business rules that drive the creation of connectivity rules  do not have a  clear default junction class or type.

Adding an edge-junction rule

1. Right-click the geometric network.
   
2. Click Properties.
   
3. Click the Connectivity tab.
   
4. Click the drop-down arrow and click the feature class for which you want to create a rule.
   
5. Click the subtype of the feature class if your feature class has subtypes.
   
6. Navigate to and check the junction feature class or subtype you want to make connectable to this edge feature class or subtype.
   
7. Default junctions are not set automatically, if you want to set a default junction type, right-click the junction subtype or feature class in the Junction subtypes list, then click Set as default. Only one default junction is allowed per edge-junction rule.
   
8. If you want to restrict the number of edges of this type that can connect to a single junction of this type, check the check box and enter the minimum and maximum number of permissible edges.
   
9. If you want to restrict the number of junctions of this type that can connect to a single edge of this type, check the check box and type the minimum and maximum number of permissible junctions.
   
10. Click OK to create the rule in the database.
    

Tips

You can use the edge–junction rules to make edge–edge rules more flexible. For example, to add a rule such that an edge of type A must have a junction of type B at one end and a junction of type C at the other end, you must first add the edge–edge rule between the edge types and the two junction types. Then, the edge–junction rules will automatically be created. Navigate to each edge–junction rule and set the edge–junction cardinality so that only one junction of each type may connect to any edge. The cardinality of a junction is the number of edge features to which it is connected. When specifying the cardinality of junctions, be aware of one exception. If the junction is connected at mid-span to a complex edge feature and nothing else, the cardinality of that junction will be two. In this instance, the cardinality of the junction is based on the number of connected edge elements, not the number of edge features. For example, for this junction to be considered valid, its cardinality should be 0 to 2. Standalone junctions may be subsumed when new edges are created if an edge–junction rule has been specified with a default junction. When a new edge feature is created and snapped to a standalone junction of any type, the junction will be subsumed by the default junction type. Setting the default junction class to be the Orphan junction feature class is a valid solution if your business rules that drive the creation of connectivity rules  do not have a  clear default junction class or type.

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