Network topology

Every trace network has a network topology. The network topology manages information about, and maintains connectivity between the features.

Information in a network topology is stored in a graph persisted as binary pages. This allows the tracing and diagram functions to read and process information about the network in an efficient manner (as opposed to retrieving information directly from features in a network). Each time a portion of the graph is accessed, that portion is cached and given a time stamp that records the last moment of access. This allows client applications to access the same portion of the graph, avoiding the need to go to the database directly, which can improve processing time.

States of a network topology

A network topology has two states: enabled and disabled. To learn how to manage the network topology state, see the Tools and commands section below.

You can use the Enable Network Topology geoprocessing tool to generate errors on network features or to enable the network topology for network functionality, such as tracing and generating diagrams.

Before the network topology is enabled, a single dirty area is displayed, covering the extent of the features spatial reference.
After the network topology is enabled, dirty areas are created to track error features and edits made to the geometry or network attributes of network feature classes.

You must disable a network topology to perform management tasks such as creating or assigning network attributes to features. It is recommended that you disable the network topology when loading large amounts of data, as this helps to reduce processing time. When you reenable a topology, the network topology is reconstructed for all trace network features.

The properties for a trace network include metadata for the network topology, found on the Network Topology tab. The metadata includes information such as the current enabled state and dirty area count, as well as the number of error features, time stamps, and duration of various network topology actions executed against the network topology.

Validate a network topology

After a network topology is enabled, portions of the network that have been edited or modified become out of date in the topology. The network topology for a given area of a network is only as current as the last time it was enabled or validated (whichever occurred last). The content you see on a map may not match what is stored in the network topology, and as a result, analytics (tracing and diagrams) that read the network topology may be based on outdated information and return inaccurate results. Dirty areas are used to mark information that is new to the network and is not reflected in the network topology. The network topology must be validated to include these changes in tracing and diagram operations.

Validating a network topology is not an automatic operation performed after every edit. You can validate the network topology using the Validate command on the Trace Network tab, or by executing the Validate Network Topology geoprocessing tool.

See Validate a network topology for more information.

During a network topology validation event, geometry and network properties are evaluated. Items found to contain invalid geometries are tracked through error features.

For the list of error situations, see Error feature management.

Two geographical extent options are available when you initiate the validation process using the Validate command on the Trace Network tab:

  • Current Extent—The network topology is validated for the current extent of the map. This option is typically used and is recommended when edits have been performed in a localized area or work zone.
  • Entire Extent—The network topology is validated for the entire extent of the network. Validating the entire extent involves a potentially heavy operation depending on the size, complexity, and number of dirty areas in your network. This operation is recommended when there are many edits scattered geographically throughout the network that need to be validated.

When you validate the network topology based on a specific extent, the dirty areas that intersect the validation extent are clipped. In the image below, the purple shaded polygons represent dirty areas, and the extent of the validate operation is represented by the black box.

Validate network topology based on current extent
The left graphic represents dirty areas before a validate operation; the extent to be validated is shown by the black box. The right graphic represents dirty areas after a validate network topology operation.

When you validate the network topology based on a specific extent, be aware of the following:

  • The evaluation extent is adjusted to include the entire dirty area when a dirty area is created from an error feature.
  • After you validate a topology, dirty areas may still be present if error features exist or if the current extent was validated and it did not encompass all of the dirty areas in the network.
  • A network feature is not guaranteed to be valid until the full extent of the feature's dirty area is validated. If there are any dirty areas associated with a network feature, it impacts tracing operations that use the validate consistency configuration option.

Dirty areas and error features

Areas of a network topology can become out of date or invalid. Dirty areas and error features are used as markers or flags to indicate these areas.

Dirty areas mark modified features on a map that are out of date in a network topology. Dirty areas are created to flag areas where edits have been made to feature geometry and network attributes or where error features exist. A network topology is validated to keep the network topology updated and remove dirty areas.

Dirty areas associated with error features (UpdateType = 3) are not evaluated when the network topology is validated and will remain until the error situation is addressed through an edit to the feature in error.

While tracing through a dirty area is allowed, it may yield unexpected results and should not be relied on. Validating the topology for the area that will be traced removes dirty areas and helps ensure the trace results reflect what is seen on the map and in the network topology.

To learn more about these concepts, see Error features and Dirty areas.

Tools and commands

There are several tools and commands you can use to manage the state of the network topology in a trace network.

Three geoprocessing tools are available that work with network topology: Enable Network Topology, Disable Network Topology, and Validate Network Topology.

You can also use the Validate command found in the Network Topology group on the Trace Network tab. This command, as well as the Validate Network Topology tool, allows you to validate a network topology for the current extent or the entire geographic extent of a trace network.

You must disable a network topology using the Disable Network Topology tool when performing configuration tasks for a trace network or performing a large data load.

You can enable a network topology to discover errors or to work with dirty areas, network diagrams, and tracing.