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Data Synchronization in Mobile Computing Systems

Lesson 08SyncML Language Features


A mobile computing system

• Consists of (i) mobile device, (ii) personal area computer in a WPAN, a computer connected by WLAN, or Internet, (iii) nearby devices, for example, printer, and (iv) mobile service provider connected by wireless


A mobile computing system

• In general, each of the devices can use different platforms

• One device may use Symbian OS, another Palm OS, and the computer on WLAN Windows OS

• Also, each one can use different languages

• For example, a device may use Java and the computer C/C++


Use of SyncML Language

• Database connector for SyncML-based mobile application synchronizes data at the device with any relational database

• SyncML-based software synchronizes data for PIM (email, calendar, memo, tasks-to-do list, or contacts list)


JCF (Jataayu client framework)

• A client framework to enable functioning of the software on different platforms


Use of SyncML client and SyncML engine

• APIs for PIM, email, and customized device application can deploy SyncML client and SyncML engine

• SyncML server for sending response to the requests from the other node, computer, or device

• Sends the messages which accompany the data and the operational results as per the messages


SyncML (Synchronization Markup Language)

• A data synchronization language based on XML (Extensible Markup Language)

• In other words, it is a markup language used for writing the codes for interfaces used for synchronization between the mobile devices and the server


XML Base of SyncML

• A language for marking up a given text with tags and attributes and it is extensively used in mobile computing


Example of XML codes

• <search_list> • …• <!- - Contact information about contacts

identified by first alphabet as R - - > • <alp_name first_character = “R”> • <contact_name> • Raj Kamal • <address> ABC Street, …. </address>• <telnumber> 9876543210 </telnumber>• </contact_name>


Example of XML codes

• <contact_name> • Raveena• <address> XYZ Street, …. </address>• <telnumber> 9848543210 </telnumber>• </contact_name>• </alp_name>• …• </search_list


Comments in XML

• Comments are not used in parsing (processing) of the codes.

• XML comments start with <!- - (less than sign, ! sign and two dashes) and ends with - - > (two dashes before the greater than sign)


Start and last tags for writing the text of a search list in between the tags

• The start tag starts with < sign• Followed by a tag name which is

search_list in this case• ends with > sign• The last tag starts with <, followed by a

slash sign, the same tag name as at the start, and > sign


Inner tag with attributes

• For example, alp_name with attribute specification first_character = “R”

• The coding format is < sign, tag name, tag attribute or attributes, > sign, followed by text associated with the given tag and attributes, < sign, slash sign, tag name and > sign


Data type definitions (DTD) file

• For an XML document, there is a data type definitions (DTD) file which specifies the rules

• For example, for the document given, it specifies that search_list is the root element and that contact_name contains the address and telephone number


XML

• A platform independent processing language

• This implies that it can be used for processing not only by Java but also by any other language

• Tags, attributes, and metadata formats in XML are standardized so that they can be universally interpreted on different platforms, machines, or networks


SyncML and Voice XML

• SyncML an open standard based on XML. It has revolutionized mobile application-development, services, and devices

• Voice XML another language based on XML and is used for communicating voice messages


SyncMLML based Information Exchange

• Between a client and server in form of an envelope representing a message

• Term message describes information• A tag and its attributes define an

envelope of a text message• Each envelope has a header followed by

body


SyncML Header and Body

• The header exists between header start and end tags

• The body which includes the commandsis present between body start and end tags

• The envelope exchanged between client and server by request and response messages


SyncML Header and Body

• SyncML message has two components(a) a header which starts with the start tag <SyncHdr> and ends with the end tag </SyncHdr> and (b) a body which starts with <SyncBody> and ends with </SyncBody>


SyncHdr

• Consists of DTD, protocol, and data (message or session) identifications

• Includes target and source information• Carries initialization information which is

required before synchronization• The initialization information enables

device authentication and includes information on available device functions


Example of SyncML Header

<SyncML><SyncHdr><VerDTD>1.0</VerDTD><VerProto>SyncML/1.0</VerProto><SessionID>session01</SessionID><MsgID>message09</MsgID><Target><LocURI>http://www.syncml.org/sync-

server</LocURI></Target>


Example of SyncML Header

<!- - LocURI means local URI. URI means Universal Resource Identifier - - >

<Source><LocURI>IMEI:49…………800</LocURI></Source> < - - IMEI is International Mobile Equipment Identity represented by a number - ->

…</SyncHdr>


Use of SyncBody

<SyncBody>…

</SyncBody></SyncML>


SyncML used between client and server

• The accompanying data (payload) is placed between a start tag and the corresponding last tag

• SyncML can be used between client and server for sending messages and data and for synchronization as it has standard defined tags, commands and protocol for exchange


Definition of the term Data store

• A term used in SyncML codes for persistent data storage

• It is also written as DataStore• Refers to storage of data in a file system

or database or in any other way in which persistency is maintained


Data store

• In the context of mobile devices, persistency means that the data remains intact till deleted even if the device power is interrupted

• Implies that a change in data during an operation is simultaneously stored and reflected at all related files in file system, database, or any other record


Example of DataStore

• Suppose a telephone number is stored in a mobile device

• The flash memory file stores it persistently and it is used in call operations


Example of DataStore

• When user modifies the telephone number in Contacts at PIM using an API, it is also stored and modified at the flash storage and will be available any time on next call

• When user deletes the telephone number in Contacts, only then the number looses persistency


Use of DataStore

• APIs, for example, PMI or email, use a Data store mechanism

• For synchronizing data using different Data store mechanisms at the nodes (client, database, file system, or server), with each one, in general, using different platforms and languages, is a difficult task


SyncML

• Can be used for sending messages of the APIs and data using the Data store mechanism at both the client and server ends


Parsing of SyncML message

• A SyncML message from SyncML client or server is used after parsing the tags, attributes and the text

• A SyncML message parsed similar to an XML document

• For example, the search list—an XML document, in Sample


Example of Using Parser

• The parser also able to retrieve the data for the contact name, telephone number, and address

• An API at the device or server can save the data using the Data store mechanism

• An API can use the data for synchronization with another API in personal area network or at server


Parse use by an API

• Assume that an API uses a parser and parses for contact names, then firstly the parser will parse for alphabet tag, then first character “ R”

• As a result, the parser gets the contact names with first character as the alphabet ‘R’

• A parser program associated with PIM API can be used to get a list of contact names


Parser

• Using the document in Sample Code, an item in the list of items will befirst line: Name Raj Kamal, second line: Address ABC Street, …, and third line Phone 9876543210


Sync ML Data Type Definitions

• SyncML, like XML, uses DTDs• These include device information DTD,

service information DTD, meta information DTD (for metadata), and main SyncML DTD

• Service information DTD represents the functional capabilities of the data objects supported by client or server


Two-way synchronization

• If a client supports vCard version 2.1 for two-way synchronization, the server must also have this capability; otherwise the synchronization session for the vCard data object cannot proceed


SyncML DTD

• Also exchanged with the message• SyncML defines a universal data

synchronization format DTD, which is exchanged with a SyncML message


Metadata in Data Type Definitions

• Metadata is information regarding the stored data or it is information about information

• Like XML document, the SyncML metadata is structured data that describes various characteristics of information-carrying elements


Data store info

• Whether Data store mechanism is database-based or file-based


Device info

• Has information about the device capability for synchronization

• Device info consists of device type, model number, manufacturer, device hardware version specification, device software specification, and device capabilities for maintaining data copies and synchronization


Metadata

• Helps in discovering and locating data or in its assessment

• The metadata data helps in the identification or management of data in the subsequent text data in the document

• Metadata considered as information about data or as information about information


Open Standard Acceptability by OMA

• Initiative for universal acceptability of SyncML is a project of the Open Mobile Alliance (OMA)

• The OMA SyncML initiative came from IBM, Motorola, Nokia, Palm, Ericsson, Lotus, Starfish, and Psion

• Later many organizations joined


Summary

• SyncML is a standard XML based language for mobile application development

• Parsing similar to XML • DataStore• SyncML DTD• Metadata

…


… Summary

• Tags and attributes• Envelope • Header • Body


End of Lesson 8SyncML Language Features

Oxford University Press 2007. All rights reserved ... · Oxford University Press 2007. All rights ... Oxford University Press 2007. All rights reserved. 18 SyncML Header ......

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