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