A quick tour of automatic metadata updates
When you view an ArcGIS item's metadata, metadata is created for the item if it doesn't already exist. Then the metadata is updated to include any properties that can be recorded for the item. For example, when you open a feature class' metadata, the current extent and count of its features will be recorded. You will always see the most current information. Metadata elements whose values were updated automatically have an asterisk (*) next to the element's name or value.
The process of automatically updating the metadata to contain an item's current properties is known as synchronization—values in the metadata are being synchronized with the item's properties.
Editing metadata works together with synchronization such that automatic updates won't overwrite information typed in by a person. Suppose an item is named parcels. When metadata is created automatically, the item's name is recorded in the metadata as a default title. If the item is renamed as cityParcels, the next time the metadata is updated automatically, the default title is changed to reflect the item's current name. If you edit the metadata and provide a more descriptive title, such as City Land Parcels, the next time the metadata is updated automatically, the title you provided won't be replaced with the item's current name.
You must have permission to edit the item's metadata for automatic updates to occur:
- For file-based items, this requires write access to the folder or network share where the item is located, and the item's files must not be read-only.
- For items in an ArcSDE geodatabase licensed with ArcGIS Server at the enterprise level, you must have permission to edit the item's data to edit its metadata.
- For ArcIMS Image and Feature Services, the ArcIMS server must have authentication enabled and you must have logged in as a user with permission to author metadata for those services.
For example, you can't automatically update metadata for data accessed from a DVD-ROM drive even if the media is writable when using a different drive.
Keeping metadata current
If you change a feature class's projection or add fields using its Properties dialog box or edit its features in ArcMap, the metadata won't be automatically updated to reflect the new projection, fields, or extent when those changes are saved. Some geoprocessing tools update an item's metadata when the process is complete, while other tools do not.
There will be periods of time when the properties recorded in an item's metadata are out of date. However, tasks you perform on an item's metadata in ArcGIS incorporate synchronization to ensure the metadata you are working with is current as long as you have write access to the metadata. Metadata is automatically updated not only when it is viewed, but before it is validated and exported, and after it is imported or upgraded.
Managing when synchronization occurs
In some circumstances, you might want more control over when automatic metadata updates occur. You can change the default behavior of ArcGIS to turn off automatic metadata updates if you prefer—updates won't occur when you view the metadata and metadata won't automatically be created if it doesn't already exist. However, this setting won't affect synchronizing metadata before it is validated and exported and after it is imported or upgraded.
You can initiate automatic updates at any time with the Synchronize Metadata geoprocessing tool. This tool gives you more control over the circumstances in which metadata is created and updated and over what information in the metadata will be updated. If you have a custom geoprocessing model or Python script that handles metadata, it should incorporate the Synchronize Metadata tool to ensure the information being handled is current.
Some organizations prefer to turn off automatic updates. When people look at metadata during the day, it isn't updated. After hours, an automated Python script updates the metadata to reflect all changes that occurred during the day. Such a script could take advantage of the Synchronize Metadata tool's option to only update metadata if it already exists.
If you access an ArcGIS item's metadata as XML and process it, you might notice many XML elements have the XML attribute Sync. When this attribute is present and its value is TRUE, the metadata element's value will be updated automatically with information derived from the item as long as the item supports updating that piec of information.
For example, when an item's name is added automatically as the default title, it looks like this when the metadata is accessed as XML: <resTitle Sync="TRUE">parcels</resTitle>. This element will have an asterisk next to it when you view the metadata because the Sync attribute is present with the value "TRUE". When you edit metadata and change the default title, the Sync attribute is removed: <resTitle>City Land Parcels</resTitle>. The element won't have an asterisk next to it when the metadata is viewed.
If an element's Sync attribute does not have the value TRUE, or if the Sync attribute is not present, the element's value won't be updated automatically.
- In ArcGIS Desktop 9.3.1 and earlier releases, you could disable automatic metadata updates for individual items using the Metadata Properties dialog box. This capability is no longer supported. If this property is set in an item's existing metadata it will be ignored by the current release of ArcGIS Desktop.
- The software components that perform automatic metadata updates are referred to as synchronizers. In ArcGIS Desktop 9.3.1 and earlier releases, a utility was provided that allowed synchronizers to be turned on or off. Turning off the metadata synchronizers provided with ArcGIS is not supported; therefore, the Set Working Synchronizers utility is no longer provided.
- In ArcGIS Desktop 9.3.1 and earlier releases, an FGDC synchronizer was provided, which exclusively updated information in metadata elements present that follow the FGDC CSDGM XML format. In the current release this same synchronizer is provided and used, but its name no longer reflects what it does—this synchronizer now exclusively updates ArcGIS metadata elements. FGDC metadata elements will not be updated automatically by the current release of ArcGIS Desktop. The FGDC synchronizer now provides the same capabilities previously provided by the ISO and Geography Network metadata synchronizers. It is not supported to disable the FGDC synchronizer programmatically.