copyright © 2001 sean c. sullivan* third party trademarks are property of their respective owners...

Copyright © 2001 Sean C. Sullivan * Third party trademarks are property of their respective owners

Data Synchronization with Data Synchronization with SyncMLSyncML** and sync4j and sync4j

Sean C. Sullivan

<sean> at <seansullivan> <.com>


Agenda

Data synchronization SyncML sync4j Q & A


What is data synchronization?

Data synchronization “is the process of making two sets of data look identical” (syncml.org whitepaper)


Data Synchronization

Conflict resolution

Datastore1

Data modifications

Datastore2

A CB C A BA CB


What is a “data synchronization protocol”?

Communication syntax and semantics for a data synchronization session

Protocol includes:– naming and identification of records– common protocol commands– identification and resolution of

synchronization conflicts


SyncML defined…“SyncML is a new industry initiative to develop and

promote a single, common data synchronization protocol that can be used industry-wide.” (syncml.org)

“SyncML is a specification for a common data synchronization framework and XML-based format […] for synchronizing data on networked devices.” (syncml.org)

“SyncML is a […] protocol for conveying data synchronization operations.” (syncml.org)


SyncML sponsors


SyncML: clients & servers

SyncMLserver

server modifications

client modifications


SyncML data identification

LUID Data

23 A

382 B

61 C

GUID Data

189 A

3982 B

89 C

Client Server

GUID LUID

189 23

3982 382

89 61


SyncML Synchronization Types

Two-way sync Slow sync One-way sync from client only Refresh sync from client only


SyncML Synchronization Types (cont.) One-way sync from server only Refresh sync from server only Server alerted sync


SyncML features

Synchronize any type of data Multiple protocol bindings

– HTTP, WSP, OBEX Security Interoperability


SyncML terminology

Message Package Command Status code

Datastore Device Info Meta Info Capabilities

exchange


SyncML and XML

Abbreviated naming convention– Ex: ”protocol version” is <VerProto>

XML prolog is not required WBXML

– WAP Binary XML


SyncML documents

<SyncML> DTD Meta info DTD Device info DTD


<SyncML> document<?xml version="1.0"?><!DOCTYPE … ><SyncML><SyncHdr>…</SyncHdr><SyncBody>…</SyncBody></SyncML>

“A SyncML Message is a well-formed, but not necessarily valid, XML document.” (syncml.org)

Contains data synchronization commands (operations)


<SyncHdr> element

<SyncHdr>

<VerDTD>1.0</VerDTD>

<VerProto>1.0</VerProto>

<SessionID>session41</SessionID>

<MsgID>msg80386</MsgID>

…

</SyncHdr>


<SyncBody> element

<SyncBody>

<Delete>

<CmdID>cmd80486</CmdID>

…

<Item>…</Item>

</Delete>

</SyncBody>


Meta Info document

Contains sync session parameters

<MetInf><Format>…</Format><Type>…</Type>…<MaxMsgSize>586</MaxMsgSize>…</MetInf>


Device Info document

Describes device capabilities

For both client and server

<DevInf>

…

<SwV>0.99</SwV>

<HwV>3.14</HwV>

…

<DevTyp>pda</DevTyp>

…

</DevInf>


SyncML commands Add Alert Atomic Copy Delete Exec Get Map

Put Replace Results Search Sequence Status Sync


sync4j

Java implementation of SyncML protocol

sync4j client & sync4j Server open source designed for J2SE platform http://sync4j.sourceforge.net


Open source licensing Licensing options:

– GPL?– LGPL?– BSD?– Apache Public License?– JDOM public license?– Mozilla Public License (MPL)?

sync4j license is virtually identical to JDOM license


sync4j audience

developers who know Java but don’t know SyncML

developers who know SyncML but may not know Java

commercial application developers & open source application developers


API design ideas SAX API

– standard set of interfaces– multiple implementations– usage model: callbacks

JDOM API– concrete classes; single implementation– root Document object contains Element

objects


API design ideas (cont.) Servlet API

– usage model: developer builds a new servlet by subclassing HTTPServlet

Auto-generate classes from DTD using an XML data-binding tool??– Sun’s JAXB– Enhydra’s Zeus


Design goals Hide complexity of the SyncML

specification from Java programmers– XML documents, XML parsing– multiple transport protocols

A complete SyncML implementation Interoperability

– with existing SyncML clients & servers


Design goals (cont.) API should be natural and familiar to

Java programmers– direct object instantiation– exceptions– use Collection API / arrays, where

appropriate– event notification via event listeners– familiar naming conventions


Design goals (cont.)

API must be familiar to developers who already know the SyncML DTD’s

API must enforce any restrictions that are defined in the SyncML specification

Target platform: J2SE


Design goals (cont.)

Modular design:– “core” protocol support– transport protocol libraries– extensible client framework– extensible server framework– client application– server application


sync4j implementation

Immutable objects Exception class for each SyncML

“status code” Declaration of constants

– public final static variables Command object hierarchy


sync4j command hierarchyAbstractCommand

ResponseCommandRequestCommand

AddCommand, DeleteCommand,

ReplaceCommand,…

ResultsCommand,StatusCommand,


sync4j toolsetTool URL

Jakarta Ant jakarta.apache.org

JDOM www.jdom.org

Apache Xerces-J xml.apache.org

CVS www.cygwin.com

log4j www.log4j.org

JDK 1.3.1 java.sun.com

JUnit www.junit.org

SourceForge www.sourceforge.net


sync4j packages

sync4j.core sync4j.client sync4j.server

sync4j.http sync4j.wsp sync4j.obex sync4j.tests


sync4j key classes

SyncMLMessage DeviceInfo MetaInfo Command classes:

– AddCommand– DeleteCommand– ReplaceCommand


sync4j.core.SyncMLMessage

Two ways to construct:– from a String of XML– from more basic sync4j objects


SyncMLMessage example 1String strXML = “<SyncML> … </SyncML>”;SyncMLMessage msg;try{ msg = new SyncMLMessage(strXML);}catch (InvalidSyncMLException ex){}catch (XMLSyntaxException ex){}


SyncMLMessage example 2SyncHeader header = new SyncHeader(...);SyncBody body = new SyncBody(...);SyncMLMessage msg;msg = new SyncMLMessage(header, body);String strXML = msg.toXML();


Algorithms Base64

– encode, decode WBXML

– encode, decode MD5

– java.security.MessageDigest


sync4j future issues

Compliance testing, interoperability tests

move to JDK 1.4?– Assert facility– Java Logging API– New I/O classes: java.nio– SSL class library


Summary SyncML is both complex and powerful sync4j hides the complexity of SyncML

from Java programmers The sync4j API is consistent with many

familiar Java programming idioms http://sync4j.sourceforge.net/


Data Synchronization with Data Synchronization with SyncMLSyncML** and sync4j and sync4j

Sean C. Sullivan

<sean> at <seansullivan> <.com>


The following slides are miscellaneous material.


SyncML authentication

<Chal> <Cred> Authentication types:

– basic– MD5

copyright © 2001 sean c. sullivan* third party trademarks are property of their respective owners...

Documents

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type of data

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interoperability slide