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When designing a mobile solution, there are some business
issues that need to be considered before the architecture can be designed. Is
the application going to be connected to the host server continuously? Or is
it going to be connected intermittently? Or rarely? These scenarios can greatly
affect the behavior of the final product.
Connection scenarios
Many companies are moving toward the continuously connected
model. With the wireless market growth that we have today, this scenario is
becoming more feasible. With the always-connected model the app should be designed
to continually poll for changes in data and transmit
those changes immediately. This puts the host and the mobile device at real
time, however it still has some drawbacks. The hardware and wireless services
are still fairly expensive, whether the technology used is blue tooth or cell
phone. Also, the range with blue tooth is limited, and cell phones have dead
zones.
Thus, many solutions involve using the intermittently connected
model. This model still has the high expenses as the continuous model, but solves
the issues with dead zones and ranges. However this introduces issues to consider
as well. The program has to have a process polling for a connection status,
so it knows when it can catch up. Also, the program has to consider coding for
disconnections during transfers.
In an attempt to solve the expensive hardware and service
issue, there is the rarely connected model. This limits the data to only be
synchronized a limited number of times in a day. Disconnections must also be
considered. Once these decisions have been answered, you need to
figure out what data needs to go to the handheld and what data needs to go back
to the server. The replication method can then be selected.
Replication Options
With SQL Server CE Edition, there are two replication options; merge replication and
remote data access (RDA). Merge replication requires a backend SQL Server 2000 server and is
implemented by distributing data between subscribers and publishers. Using RDA, you can execute
a pass through SQL statement, which will be executed on the backend or the program can be set up
to push or pull data.
Getting Started
No matter which replication method you choose, you
cannot connect unless you have an IIS server configured to act as a bridge to
the database. To do this, copy the sscesa10.dll from the directory Microsoft
SQL Server CE\Server\ to a directory on your IIS server and add a virtual directory
to it. Note: This cannot by default run in the current directory on an NTFS partition
due to insufficient read / write permissions. If you choose to use this directory,
add 'Read & Execute' permissions to the IIS anonymous user's (IUSR_) account
on that directory.
First, kick off the virtual directory wizard.
Then, give the alias a name.
Point the virtual directory to the directory where
you have located the sscesa10.dll file.
Set the 'Execute' check.
Done!
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