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Should I cascade or embed one service within another?
Generally, cascading map services is not recommended and could introduce unforeseen problems into both ArcGIS Server and ArcIMS environments.
A cascading service is the notion of a published map service being added to a map document (MXD) and re-published as a map service.
With the 9.3 release, it is not possible to re-publish a password protected map service through ArcGIS Server (even as the owner of the original service).
Some of the known issues with cascading services include:
Third party services
Re-publishing a third party map service or one that is not managed by your organization is not supported. The inability to ensure stability, up-time, or even inspect the original map service at a service level, can create problems for the re-published map service. The following services (to name a few) should not be republished:
-Third party WMS services
-Third party image services
-Third party ArcIMS or ArcGIS Server map services
ESRI Support does not have the ability to troubleshoot a map service that is not directly manage.
Another potentially problematic workflow involves cascading a service and attempting to create a map cache. The map cache mechanism makes many calls for each layer at varying extents and resolution. Not every service provider can keep up with the requests required to build a map cache at the speed the cache mechanism requires. A cascading map service that draws upon a non-ESRI map server may not be able to produce enough maps/tiles per second to satisfy the cache generation process. Additionally, many third party map services have a cap on the map image dimensions that can be requested. This becomes problematic for the map caching tools, which requests an area up to 4096 x 4096 pixels at a time. A complete cache failure or an incomplete cache with blank tiles could result.
Finally, caching third party map services could result in legal issues if proper rights to the original data are not obtained from the owner.
ESRI cannot support, nor guarantee a cache attempt, from a third party map service or any cascaded service.
Working with cascading services
There have only been two identified situations that may require the use of cascading services. Caution is emphasized if these workflows must be used.
The first scenario involves use of the ArcGIS Data Appliance. This appliance contains tiles in the WGS84 geographic coordinate system. If there is a requirement to overlay a service whose cache uses a different coordinate system, it may be necessary to add both services to an MXD and republish. The map service can reproject the cached tiles on the fly.
This could introduce performance concerns, and the ability to zoom to specific cache scales will be lost. If possible, avoid this scenario by matching other services to the WGS84 coordinate system used by the ArcGIS Data Appliance.