At the start of my dabblings in SyncML, I expected to have to implement a significant chunk of the SyncML protocol myself. Fortunately, since then two factors have made this unnecessary: first, the publication of the previous two articles (see part 1 and part 2) caught the attention of those working on SyncML, and they've let me know about their work; and second, the increasing availability of mobile phones and PDAs with SyncML inside has led to increased activity in this field.
The SyncML Reference Toolkit (RTK), though hosted on SourceForge (see Resources), is a relatively well-kept secret. It was developed by the SyncML consortium itself. Of course, members of the consortium have their own SyncML-based products to sell. So while the open-source RTK is a wonderful contribution, it has not been published too widely, in order not to undermine the business of the SyncML designers. For this reason, no sample applications are delivered with the toolkit.
The RTK is a relatively mature product, and compiles on both Windows and Linux platforms. Linux users have to do some fudging, however, as little bugs such as expecting case-insensitive file names are not entirely absent from the toolkit. The toolkit comprises a comprehensive C library for creating, sending, receiving, and parsing SyncML messages. It supports both XML and WBXML encodings, and HTTP (for synchronization over the Web), WSP (for use over WAP) and OBEX (for use over IrDA or Bluetooth) transports.
The RTK is accompanied by a reasonably complete, though not overly detailed, set of API documentation. Some parts of the documentation seem to be at variance with the library itself, so be prepared to start poking through the source and header files. Reflecting the fact that SyncML has so many components, the RTK is somewhat sprawling. C is, of course, a superior language for portability, but it struck me as I investigated the toolkit that something in, say, Python would be a lot more accessible.
This toolkit seems like a good choice for long-term SyncML development, especially if you want the advantages of speed and Windows/Linux code portability. Don't, however, expect to whip up a quick hack with it. If you're looking for support, then try the YahooGroups SyncML mailing list (see Resources), as discussion of the RTK forms the main part of the traffic.
I mentioned earlier the lack of examples using the RTK. However, one example that is an absolute gem is provided by Mirko Mrowczynski. See Resources for details on how to obtain this example. Mirko's Web page is in German, which helps explain why this example is hard to find for English speakers. His sample application makes a good starting point for programming with the RTK.
Pros: C is a great common denominator; authoritative source; mature product; active support mailing list.
Cons: Large API; unfriendly documentation; hard to get started.
PHP implementation of SyncML Server
The most immediate use you might have for SyncML is to use it to back up the data on your phone. This is the application that Nicolas Bougues has targeted with his implementation of a SyncML server. Nicolas' code is written in the popular Web scripting language PHP, and uses a MySQL database for back-end storage. It only supports the XML encoding of SyncML, not the WBXML one, and was developed against the Sony Ericsson P800 phone. The P800 only performs synchronization over HTTP connections, either using a GPRS/GSM connection, or when connected to a computer through its cradle.
To use it you need to download the scripts (see Resources), unpack them on your Web server, and create the required database in MySQL. Nicolas' code supports the synchronization of the address book, calendar, and jotter applications. The MySQL database stores the vCard, vCalendar, and vNotes representation of the data. For instance, at the recent WWW2003 conference in Hungary I dined out with a group of friends, and made a note on my P800 of what I ate. When synchronized into the database, it appeared as shown in Listing 1.
Listing 1. vNote of meal eaten at Restaurant Fatál in Budapest, Hungary
BEGIN:VNOTE
VERSION:1.1
DCREATED:20030523T192529Z
LAST-MODIFIED:20030523T211027Z
BODY;ENCODING=QUOTED-PRINTABLE:
food=0D=0Asoup=20540=0D=0Aduck=201690=0D=0Abeer=20590=0D=0A
END:VNOTE
|
While obviously not industrial strength (Nicolas includes various strenuous disclaimers), this application has set me thinking about neat things I could do with the phone: for instance, using it to write Web journal entries offline and send them live via the database. It's a great starting point for further exploration.
Pros: Fun and useful way to start experimenting with MySQL.
Cons: Immature, server-only implementation; PHP not suited for client-side development; no WBXML support.
When I first investigated SyncML, Sync4J was one of the projects I checked out. At that time, no releases had been made. In fact the first beta release of the software was made very recently, at the beginning of May 2003 (for download details, see Resources). Sync4J has taken some time to emerge, but looks as though it has the best prospects for a large-scale deployment of SyncML. In addition to being a SyncML API, Sync4J also provides a SyncML server and client tools.
Sync4J requires a J2EE environment in which to run, using Java 1.4. For those like me who don't usually live in the J2EE world, Sync4J makes it easy by providing a JBoss installation. The advantages of a J2EE environment are plain if that's where your current infrastructure lies. If it isn't, then you may find the associated resource overhead somewhat odious. However, as the server can use the file system as its synchronization store, you don't necessarily need to use Java code for every part of your project.
In testing, I was unfortunately unable to get my Sony Ericsson P800 to synchronize properly against Sync4J, although I believe that the bug behind this is being addressed by the developers. In fact, Sync4J has a strong support community, with separate mailing lists for users and developers, and is funded in part by a commercial organization, Funambol.
Pros: Professional implementation; good foundation for a large system; Java; likely to be long-lived.
Cons: Large resource overhead; J2EE application server required.
Just in case you thought I'd not covered all the main programming languages yet -- here's a SyncML library written in C++. Despite the fact that development on this project is somewhat stalled (no change since April 2002), I was quite impressed with LibSyncML. It is a nicely assembled project, with the same thoroughness in the construction of the distribution as you would expect from GNU tools.
Being in its infancy, LibSyncML has little documentation. On the other hand, it has quite a few examples. Reading through the source, I was impressed with the clean encapsulated API that the library presents, which was certainly a contrast to the SyncML Reference Toolkit mentioned above. If you feel like implementing SyncML yourself and are happy with C++ programming, I would say this is the best project to get involved in. The author has certainly set out in the right direction.
Pros: Straightforward autotools-based compilation; API much cleaner than RTK.
Cons: Early stage; maintainer no longer has time to carry on with it; C++ isn't everyone's cup of tea.
Open source SyncML implementation is still in an early phase. The range of open source tools I surveyed are all unsatisfactory in some way, though most of them represent a viable and sensible alternative to implementing SyncML by oneself. I'm pleased to be able to abandon my plans for a ground-up implementation of SyncML.
So, at the end of several months' interest in SyncML, where am I? Frankly speaking, not as far on as I'd like to be. Despite its simple concepts, SyncML is actually quite hard to implement -- especially when compared to its predecessor in the mobile world, IrMC synchronization. The cloud of committee-designed specifications around mobile XML standards can be baffling, and is often troublesome. The standard of the specifications themselves is not to up the level one normally gets from the World Wide Web Consortium.
In my own implementation efforts, understanding and implementing WBXML (a binary encoding of XML) ended up diverting me from my main goal for an unwelcome amount of time. Modern devices remove the need for the "W*" family of specifications, and I'm glad to see them receding.
SyncML was originally designed in a world of very low resource devices, before the standardization of SOAP and the ready availability of higher-bandwidth mobile Internet access. If the protocol were to be designed today, it might well look a lot different, and would almost certainly be easier to implement. Definitely, some kind of SyncML-Lite that streamlines the feature set and expectations of implementations is needed.
- Try the open source SyncML
Reference Toolkit hosted on SourceForge.
- Get Mirko Mrowcyznyski's example SyncML
application which is in German and utilizes the SyncML reference toolkit (RTK).
- Check out the YahooGroups SyncML
mailing list. It largely centers on the SyncML Reference Toolkit and its deployment.
- Read Nicolas Bougues' PHP implementation of
SyncML which offers a good starting point for the willing hacker.
- Sync4J is a
large-scale J2EE implementation of the SyncML protocol.
Download it with or without JBoss.
- Try the separate Sync4J mailing
lists for users and developers.
- Preview LibSyncML, an
early-stage implementation of SyncML in C++. Example server and
client tools are available.
- Read all of Edd Dumbill's previous XML Watch columns.
- Find more XML resources on the developerWorks XML zone.
- Rational Application Developer for WebSphere Software helps Java™ developers rapidly design, develop, assemble, test, profile and deploy high quality Java/J2EE, Portal, Web, Web services and SOA applications.
- Find out how you can become an IBM Certified Developer in XML and related technologies.
Edd Dumbill is managing editor of XML.com and the editor and publisher of the XML developer news site XMLhack. He is co-author of O'Reilly's Programming Web Services with XML-RPC, and co-founder and adviser to the Pharmalicensing life sciences intellectual property exchange. Edd is also program chair of the annual XML Europe 2002 conference. You can contact Edd at edd@xml.com.
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