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What are the differences between ArcGIS Desktop and ArcGIS Server Mobile ADF data-sharing models?
Both ArcGIS Desktop and the Mobile ADF allow users to check out spatial data for environments where network connectivity is slow or does not exist. The approaches taken in the two platforms are different in the 9.2 release and not compatible between ArcGIS Desktop and mobile clients. The Desktop model is a full geodatabase replication model, whereas the Mobile ADF model is an implicit two-way data synchronization model.
ArcGIS Desktop creates child replicas (geodatabases participating in replication) for each user. Each combination of a child and parent replica is called a replica pair. Additionally, each replica stores information in its data dictionary about its related replicas. The child replica is a full geodatabase, with all its functionality and capabilities. Therefore, it can also act as a parent replica in a multi-generation geodatabase replication model. When the connection is available, users have an option to post updates, many times using a two-way communication between the parent and the child replica. It can only post updates once by checking in the data, thus completing the edits and removing the child replica. One of the data requirements for ArcGIS replication, in addition to write access to the data, is versioning – all data must be registered as versioned without the option to move edits to base. Also, each dataset must have a GlobalID column.
The Mobile ADF approach is exclusively based on the model similar to the two-way synchronization model. The data between the client and the server can be exchanged many times both to update the client with the changes stored in the server and to progressively post edits performed on the client to the server field. Unlike the Desktop model, this does not require server side versioning. The Mobile ADF model works equally well with both versioned and non-versioned geodatabases. Furthermore, in this model there is no concept of a parent-child paring, therefore many field users can be provided with the same database for their mobile work. This may be very useful in large field deployments when the installation of software and data can be made quickly off a single setup. When working with a versioned server database, each client is capable of creating a unique version to ensure integrity of the data. Unlike in the replication model, when the field edits are completed, the client database remains of the device and can be kept up to date by re-synchronizing it with the server, and as a result, it can be used in future edits. Finally, the Mobile ADF model is limited to the equivalent of a single-generation replication; the mobile database cannot serve as a parent data source for another mobile client.
The differences between spatial databases in Mobile ADF and ArcGIS Desktop are not limited to the synchronization model. The Mobile ADF represents a flat view of the geodatabase. It only supports simple feature classes, and does not support related tables, complex types, like networks, representations, or topology. It is also optimized for use in mobile devices and for communication over slow, wireless networks. Data updates in the Mobile ADF transmitted to the server are limited only the deltas, or to fields that have changed, instead of entire features. This greatly reduces communication overhead and decreases the cost of exchanging the data between the server and the client in the field.