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Basics of how Sync Services Works

Written for Office 2004

by Andy Ruff MacBU Program Management

I'd like to offer a bit different way to think about Sync Services. It's not the way that it appears within any user interface--be it Apples applications (iCal/Address Book/iSync/.Mac), Entourage, or any other application. It is the way Sync Services works from a "programmer's" perspective. The fact that the back-end, programmer stuff doesn't align necessarily to the easy-to-use front-end stuff is most likely testament to Apples ability to create elegant software, though it leads to some confusion at times.

Apple's iCal, Address Book, iSync, .Mac, Microsoft Entourage, and any other application hooked into Sync Services syncs their items with what is known as the Sync Services Truth. When a new event is added in Entourage, it goes to the Truth. When a new event is added to iCal, it goes to the Truth. When iSync needs to know what events need to be added to a device, it asks the Truth. The Truth knows all :).

Entourage is not synchronizing with iCal but with the Truth. Entourage watches for new items, removed items, and modified items within the Truth. Address Book, iCal, .Mac sync, and iSync all do the same. If you turned on Sync Services in Entourage and deleted iCal from your computer--Entourage should still be able to sync through iSync. The confusion typically is that iSync and .Mac sync preferences use the iCal and Address Book application icons rather than the generic, application agnostic icons for events, contacts, etc.


There's a dialog that pops-up in Entourage when you turn on synching of a calendar or address book that asks something like: "You have enabled Sync Services for a folder, do you want to?"

  • Replace Entourage items with Sync Services items
  • Replace Sync Services items with Entourage items
  • Merge Entourage items with Sync Services items

Entourage 2008 modified the choices like this:

The "Replace Entourage items" option will delete all items in Entourage and override them with the contents of the Sync Services truth. You'd want to do this if you haven't used Entourage in a while or you consider your cell phone's address book the primary "rule" for your contacts.

The "Replace Sync Services" option makes Entourage the short-term rule. All contents within your truth will be deleted and replaced with Entourage items. In this case, all contacts in your Address Book app would be deleted and then replaced with those from the address book selected in Entourage. This is useful if you've been living in a two-address book world (as I have) with Entourage as your primary address book.

The "Merge" option is the safest option. Nothing gets deleted. Items in the Sync Services truth go into Entourage and items within Entourage go into the Sync Services truth. This can be a bit messy, causing duplication, or unwanted items--but your data is pretty much guaranteed to remain. Generally, I'd always recommend "Merge" with a clean-up later on (remember, all future deletions/modifications will get synched from this point forward).

After selecting one of these options, all changes in anything that talks to the truth will be synchronized to any application that listens.


Part of Sync Services is a set of schemas that define what's in a calendar event or what's in a contact. When a property for an item doesn't show up in iCal or Address Book from Entourage or vice versa, it's typically because the schema doesn't support these properties or either app(s) doesn't support the property. For example, Entourage categories don't show up in iCal or Address Book because there's no long-term reliable category mapping in iCal or Address Book (yes, iCal supports calendar groups, but Entourage items may contain many categories while iCal items only one). The issue goes both ways, iCal allows several types of reminders not supported by Entourage--they just won't sync over into Entourage.

This is best exemplified by Entourage Notes and Sync Services. Apple doesn't have an app equivalent to our Notes functionality that is hooked into Sync Services. As such, we had to define our own schema--providing Sync Services with a definition of what we believe a note is. Other developers are free to use our schema just as we did with Apple's events, contacts, and tasks. If they did, any note created in their apps would show up in Entourage. Pretty cool. However, as of now, only Entourage knows about this schema--so only other copies of Entourage will synchronize with these notes. If you hook up two Macs to sync over a .Mac account and enable Entourage Notes in your .Mac Sync Preferences, you should see notes created on one machine show up on the other and vice versa


I'm long-winded :). Here's some possible ideas for you for your cell phone issue. Try creating a "cell phone" group within Address Book. You'll have to manually update the cell phone group as it won't map 1:1 to your category in Entourage. Another option would be to place the term "cell phone" within the Notes field of each contact in Entourage. Then create a Smart Group in Address Book that finds all items with notes containing the phrase "cell phone." I agree, it's still not as easy as it could be.

-- Andy Ruff MacBU Program Management

Entourage Weblog: http://blogs.msdn.com/entourage/