Palm OS Programming, 2nd Edition

The Logic of Syncing

Because handhelds can be synced to more than one desktop machine, there are two different forms of syncing. These two forms are:

Fast sync

This occurs when the handheld is being synced to the same desktop machine that it was synced to the previous time.

Slow sync

This occurs when a handheld is synced to a different machine from its previous sync. In such cases, a set of problems arise in determining what changes have been made.

Before discussing either type of syncing, however, we need to explain some of the difficulties that can arise in situations in which the same record can be modified in more than one location. After we give you some rules for handling these conflicts, we discuss fast syncing and then turn to the more difficult slow syncing.

Thorny Comparisons—Changes to the Same Records on Both Platforms

There are some very thorny cases of record conflicts we have to consider. When you give users the capability of modifying a record in more than one location, some twists result. The problem occurs when you have a record that can be changed simultaneously on the handheld and on the local database, but in different ways. For example, a customer record in our Sales application has its address changed on the handheld database and its name changed on the local database. Or a record was deleted on one platform and changed on another. The number of scenarios is so great that some formal rules are required to govern cases of conflict.

The rule—first, do no harm ...