Haddad also pointed out that with each successive iOS release since the introduction of iCloud, the under-the-hood mechanics and functionality for its syncing have improved. He's optimistic that the trend will continue with iOS 7.
Rich Siegel of Bare Bones Software sees the Datastore API as unattractive to many developers in the Apple ecosystem for another reason entirely: "There is no SDK for OS X," he pointed out, "which makes it an instant nonstarter for any developer who needs to synchronize data between desktop computers, whether or not mobile devices are involved."
That's not the only downside for Datastore, either. All three developers mentioned that iCloud doesn't require users to sign up for a new account, and Dropbox does. That said, "Dropbox has become ubiquitous enough that it is highly likely that someone who downloads your app will already have a Dropbox account and will only need to authenticate with it," said Pierce, but that's less assured—and less seamless—than an iCloud-backed option.
What Dropbox does and doesn't do
"In theory at least, iCloud used with Core Data offers ... powerful tools to work with relational data, an extensive query language, [and] tools for working in multi-threaded environments," Pierce said. Datastore can't match that functionality. It can't perform sorted queries, queries that require joining bits of data from multiple datasets, or paginate results—all fairly basic database functionality that's (at least currently) beyond the scope of what Dropbox offers.
Such features, Pierce said, are a must-have for "larger datasets that cannot all be held in memory." But he added, "I think the Dropbox Datastore can really shine for apps with small datasets."
Siegel seemingly concurred: "The question of which service a developer chooses should, I think, revolve around what meets the technical needs of the developer on the way to shipping the product that best suits their customers' needs."
If Apple has cause for concern, Perry says, it's all that cross-platform support that Dropbox offers. "iCloud represents [Apple's] attempt to lock users into their ecosystem ... If Dropbox catches on as a mainstream sync solution, it makes it easier for users to pack up and take their data to other mobile platforms like Android, or even other desktop platforms like Windows."
That syncing feeling: Which sync service developers will choose?
"I can imagine a developer will find the Dropbox Datastore API worth a look," Siegel said, "if their product is not on OS X and they have an interest in structured key/value/record/table database syncing and/or need a solution for both iOS and Android." If a developer is instead targeting the Apple ecosystem exclusively, Siegel said, iCloud "is the platform-vendor-sanctioned solution, offers integration with the existing platform document and data storage APIs, and is available as part of the stock OS install at no charge."
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