1 <?xml version="1.0" encoding="utf-8"?>

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     7     Nokia Corporation - initial contribution.

     8 Contributors: 

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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-F79E4F18-19E2-577E-8409-8B82BD48AC66" xml:lang="en"><title>XML

    13 Framework Overview</title><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <p>The XML Framework is a collection of components for event-based XML parsing

    15 and provides content-processing architecture. </p>

    16 <section><title>Purpose</title> <p>The XML Framework provides configurable

    17 features for parsing XML and <xref href="http://www.w3.org/TR/wbxml/" scope="external">WBXML</xref> (WAP

    18 Binary XML), with options for validating against a specification and auto-correcting

    19 for spelling errors in the validated text, using a single interface. It is

    20 based on the <xref href="http://www.saxproject.org" scope="external">SAX</xref> (Simple

    21 API for XML) specification. </p> </section>

    22 <section><title>Required background</title> <p>You must have a basic understanding

    23 on XML before using XML Framework. </p> </section>

    24 <section><title>Key concepts</title> <p>The following are the key concepts

    25 of XML Framework: </p><p><b>Attribute</b></p><p>A name-value pair separated

    26 by an equals sign, for example <codeph>author="Jane Austen"</codeph>  </p><p><b>Attribute

    27 type </b></p><p>One of certain data types defined for attributes, for instance <codeph>CDATA</codeph>. </p><p><b>Client</b></p><p>An

    28 application which uses the XML framework for parsing or generating a document. </p><p><b>Document

    29 Type Definition (DTD) </b></p><p>A document which defines a particular use

    30 of XML entities (the names, attributes and values permitted). </p><p><b>Extension</b></p><p>WBXML

    31 extends XML syntax with extension tokens which are used differently by different

    32 applications. For example, extension token is used to refer to a string table

    33 created specifically for each message and transmitted in the introduction

    34 of the message. </p><p><b>Parser</b></p><p>It is an interface to the XML framework

    35 which allows a client to access the parser plug-ins, which are specific for

    36 a mark-up language. For example, XML Expat Parser and WBXML Parser. </p><p><b>String

    37 dictionary collection</b></p><p>A class that holds a collection of string

    38 dictionaries. </p><p><b>String dictionary plug-ins </b></p><p>The XML Framework

    39 allows strings to be stored in DTD document, XML namespace or WBXML code page

    40 in an ECOM plug-in that could be accessed as required by the parser and the

    41 client. These plug-ins are referred as string dictionary plug-ins. </p><p><b>String

    42 pool</b></p><p>A string pool is a mechanism for storing strings in a particular

    43 way using which the strings can be compared quickly. </p><p><b>String table</b></p><p>A

    44 WBXML document is encoded and decoded using a table of frequently encountered

    45 strings which the body of the document references by index to compress the

    46 data. </p><p><b>Uniform Resource Identifier (URI)</b></p><p>The web address

    47 associated with a prefix. For instance, <codeph>http://www.w3.org/XML/1998/namespace</codeph>. </p><p><b>WBXML</b></p><p>WAP

    48 Binary XML (WBXML) is a binary representation of XML. It was developed by

    49 the Open Mobile Alliance as a standard to allow XML documents to be transmitted

    50 in a compact manner over mobile networks and was proposed as an addition to

    51 the World Wide Web Consortium's Wireless Application Protocol family of standards. </p> </section>

    52 <section><title>Architecture</title> <p>The following diagram illustrates

    53 the XML framework, consisting of client and a parser: </p> <fig id="GUID-9EE24AE6-17F1-59A2-9AF8-9A1068393053">

    54 <title>              Block diagram of XML framework            </title>

    55 <image href="GUID-CA1CE18E-DB40-5608-BE09-3767FB094AB2_d0e432397_href.png" placement="inline"/>

    56 </fig> <p>The XML framework consists of classes which model the main constituents

    57 of the architecture - the framework as a whole, the parser plug-ins and extensions

    58 to XML, the content processor chain and the content handler mechanism. </p> <p>The

    59 XML and WBXML parsers convert the contents of a document to UTF-8 format.

    60 This is to ensure that extended characters are not lost from the document

    61 by the String Pool. Expat is the engine behind the XML parser plug-in. </p> <p>The

    62 XML Framework allows strings to be stored for a particular DTD, XML namespace

    63 or WBXML codepage in an ECOM plug-in that can be accessed when requireded

    64 by the Parser and the Client. These plug-ins are referred as String Dictionary

    65 Plug-ins and they are managed through a string dictionary collection object.

    66 See <xref href="GUID-0D16866C-F46B-5A2B-B974-324278588A1B.dita">String Dictionary</xref>  </p> <p>Libxml2

    67 provides XML processing, parsing and validation APIs. See <xref href="GUID-0129AE17-B171-5CD5-8542-1DB738CBAB8B.dita">libxml2</xref>. </p> <p>Plug-in

    68 1 and Plug-in 2 are examples of optional processors, which may be chained

    69 together with the parser output to allow further processing of the data, before

    70 the client receives it. Such plug-ins can be a DTD validator or a document

    71 auto-corrector. The chain is not limited to just two plug-ins. </p> <p><b>Parser

    72 framework</b> </p> <p>The XML framework contains Parser framework which is

    73 represented by the <xref href="GUID-3C824E3B-68AB-31C5-A3D7-26A73B53D076.dita"><apiname>CParser</apiname></xref> class. A client with an XML

    74 document to be parsed creates a <xref href="GUID-3C824E3B-68AB-31C5-A3D7-26A73B53D076.dita"><apiname>CParser</apiname></xref> object and calls

    75 its parse functions. <xref href="GUID-3C824E3B-68AB-31C5-A3D7-26A73B53D076.dita"><apiname>CParser</apiname></xref> obtains the data about plug-ins

    76 and the document to be parsed from<xref href="GUID-A6CF939C-110C-3FA4-8C2E-0B48C04D9CFB.dita"><apiname>CMatchData</apiname></xref> and <xref href="GUID-D79A2F59-8DC1-3493-92F6-2E1337CD9405.dita"><apiname>RDocumentParameters</apiname></xref> classes

    77 respectively. </p> <p>The parser framework conforms to the event-based SAX

    78 specification. It outputs an event when it starts or finishes reading one

    79 of the following: </p> <ul>

    80 <li id="GUID-A229D260-A15A-5EC6-8808-60577D988073"><p>a document </p> </li>

    81 <li id="GUID-4ED3BF2E-0CB8-54E3-B332-C60A032FD8F5"><p>a start tag </p> </li>

    82 <li id="GUID-57CB6A28-6F7B-5D75-AB59-BA4429374D23"><p>an end tag </p> </li>

    83 <li id="GUID-2CB3BFDA-425D-5936-B2D0-1A5459D56813"><p>a prefix mapping </p> </li>

    84 <li id="GUID-181F5F9F-D9D2-5E42-96F4-BACD64B2ABBF"><p>a processing instruction </p> </li>

    85 <li id="GUID-FB122F10-A946-5661-8A9B-A42877FB0DAC"><p>character data </p> </li>

    86 <li id="GUID-C0C9C2C4-862B-55CF-904F-E761518275DB"><p>ignorable white space </p> </li>

    87 </ul> <p>For more information on XML-related concepts, refer to W3C or similar

    88 sources. </p> <p><b>Parser plug-ins</b> </p> <p>The <xref href="GUID-3C824E3B-68AB-31C5-A3D7-26A73B53D076.dita"><apiname>CParser</apiname></xref> is

    89 the interface to the XML framework allowing the client to access the parser

    90 plug-ins, each one of which is specific to a mark-up language (e.g. XML, WBXML).

    91 Individual parser plug-in implements the <xref href="GUID-6F334B00-8026-3FA3-AE96-B0A511030B7B.dita"><apiname>MParser</apiname></xref> interface.

    92 It is associated through the <xref href="GUID-5F929E9F-E895-3DA6-8072-28C4B8B1CF81.dita"><apiname>TParserInitParams</apiname></xref> class, with

    93 a character set converter (to convert other formats to Unicode), a string

    94 dictionary and an element stack. </p> <p>The Symbian platform framework is

    95 delivered with three parser plug-ins, two for XML and one for WBXML. </p> <ul>

    96 <li id="GUID-CAAD5966-F37D-5A9C-A240-911B6683B315"><p>The first XML parser

    97 consists of <xref href="GUID-278C5360-5023-3406-98B1-BEB7AD2A4A9D.dita"><apiname>CXmlParser</apiname></xref> class, which is wrapped around the <xref href="GUID-D7864E56-D87D-3EC0-BA5F-804BE8F532FF.dita"><apiname>CExpat</apiname></xref> class,

    98 an implementation of the stream-based Expat parser. </p> </li>

    99 <li id="GUID-4A7DAA35-DD92-547F-BF81-232521F21A79"><p>The second XML parser

   100 consists of <xref href="GUID-F6E8B374-12D7-34FE-A1AA-F8B2BCA45B0A.dita"><apiname>CXMLEngineSAXPlugin</apiname></xref> class, which encapsulates

   101 the SAX parser of the <codeph>libxml2</codeph> component. It is not available

   102 if the Symbian platform build excludes this component. </p> </li>

   103 <li id="GUID-A5342749-34E7-5AD4-A5E4-FD46703F4AC7"><p>The WBXML parser is

   104 implemented as the <xref href="GUID-98F7BF57-BDC8-3BA4-9141-7DEDFFF64DB0.dita"><apiname>CWmxmlParser</apiname></xref> class. </p> </li>

   105 </ul> <p><b>Extensions to XML</b> </p> <p>The XML framework provides extensions

   106 to XML. At present WBXML is implemented. WBXML requires use of string dictionaries

   107 and extension tokens to store the element strings specific to the WBXML, which

   108 are represented by the <xref href="GUID-094A4884-182E-3A10-80F5-85A925020BC1.dita"><apiname>RStringDictionaryCollection</apiname></xref>, <xref href="GUID-FF04F0FE-771D-3197-BA3F-BB34C78E2F65.dita"><apiname>MWbxmlExtensionHandler</apiname></xref> and <xref href="GUID-1D0F59D7-574C-3485-9AB7-499712E5F20B.dita"><apiname>TExtensionTokens</apiname></xref> classes. </p> <p><b>Content processors</b> </p> <p>Content processors are

   109 plug-ins which perform further operations on the output of a parser plug-in.

   110 They implement the <xref href="GUID-7942EDC6-6571-3423-8ECA-D3DB68A78CB6.dita"><apiname>MContentProcessor</apiname></xref> interface and are

   111 associated through the <xref href="GUID-892978EC-1BE4-3356-ADB1-1E7EAB83C686.dita"><apiname>TContentProcessorInitParams</apiname></xref> class,

   112 with a string dictionary and element stack. They are organised into chains

   113 by the <xref href="GUID-0DFBB9EA-5A0E-3B4F-AD60-3CCD35090B40.dita"><apiname>MContentSource</apiname></xref> class which directs the output of

   114 each plug-in to the next plug-in in the chain. </p> <p><b>Content handlers</b> </p> <p>A

   115 client application which is designed to react to the output of the XML framework

   116 event must implement the <xref href="GUID-A6B8386B-29F6-3BEC-9D77-D8E0900DEAC2.dita"><apiname>MContentHandler</apiname></xref> interface. The

   117 functions to be implemented correspond to the SAX specification discussed

   118 in the Parser Framework section. </p> </section>

   119 <section><title>APIs</title> <p>The XML Framework exports the following APIs: </p> <table id="GUID-7EBF7AA5-B11F-5C40-93A7-685E8714DE92">

   120 <tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

   121 <thead>

   122 <row>

   123 <entry>API</entry>

   124 <entry>Description</entry>

   125 </row>

   126 </thead>

   127 <tbody>

   128 <row>

   129 <entry><p> <xref href="GUID-D7864E56-D87D-3EC0-BA5F-804BE8F532FF.dita"><apiname>CExpat</apiname></xref>  </p> </entry>

   130 <entry><p>Encapsulates the Expat XML parser. </p> </entry>

   131 </row>

   132 <row>

   133 <entry><p> <xref href="GUID-278C5360-5023-3406-98B1-BEB7AD2A4A9D.dita"><apiname>CXmlParser</apiname></xref>  </p> </entry>

   134 <entry><p>Implementation of the stream-based Expat parser. </p> </entry>

   135 </row>

   136 <row>

   137 <entry><p> <xref href="GUID-F6E8B374-12D7-34FE-A1AA-F8B2BCA45B0A.dita"><apiname>CXMLEngineSAXPlugin</apiname></xref>  </p> </entry>

   138 <entry><p>Encapsulates the SAX parser of the <codeph>libxml2</codeph> component. </p> </entry>

   139 </row>

   140 <row>

   141 <entry><p> <xref href="GUID-3C824E3B-68AB-31C5-A3D7-26A73B53D076.dita"><apiname>CParser</apiname></xref>  </p> </entry>

   142 <entry><p>Represents the entire parser framework. </p> </entry>

   143 </row>

   144 <row>

   145 <entry><p> <xref href="GUID-A6CF939C-110C-3FA4-8C2E-0B48C04D9CFB.dita"><apiname>CMatchData</apiname></xref>  </p> </entry>

   146 <entry><p>Consists of the data of the plug-ins. </p> </entry>

   147 </row>

   148 <row>

   149 <entry><p> <xref href="GUID-98F7BF57-BDC8-3BA4-9141-7DEDFFF64DB0.dita"><apiname>CWmxmlParser</apiname></xref>  </p> </entry>

   150 <entry><p>WBXML parser implementation. </p> </entry>

   151 </row>

   152 <row>

   153 <entry><p> <xref href="GUID-D79A2F59-8DC1-3493-92F6-2E1337CD9405.dita"><apiname>RDocumentParameters</apiname></xref>  </p> </entry>

   154 <entry><p>Consists of the data about the document to be parsed. </p> </entry>

   155 </row>

   156 <row>

   157 <entry><p> <xref href="GUID-AE53784D-B405-34D8-9A93-ACDE6F8ECA44.dita"><apiname>RElementStack</apiname></xref>  </p> </entry>

   158 <entry><p>Data structure used to store XML elements and check the tag ordering. </p> </entry>

   159 </row>

   160 <row>

   161 <entry><p> <xref href="GUID-094A4884-182E-3A10-80F5-85A925020BC1.dita"><apiname>RStringDictionaryCollection</apiname></xref>  </p> </entry>

   162 <entry><p>Holds a collection of dictionaries requested by the user. </p> </entry>

   163 </row>

   164 </tbody>

   165 </tgroup>

   166 </table> </section>

   167 <section><title>Typical uses</title> <p>The following tasks can be performed

   168 using XML Framework: </p> <ul>

   169 <li id="GUID-0FD3D44F-83D3-57C4-9C3E-063450A8078E"><p>Parsing an XML document. </p> </li>

   170 <li id="GUID-9C4511A4-49FE-53FA-83A4-9B55D58B0905"><p>Choosing a parser plug-in. </p> </li>

   171 <li id="GUID-6B09BFFF-8BBC-5FDC-B1CE-339C893C5164"><p>Using content processor. </p> </li>

   172 <li id="GUID-EC907C49-599B-5C60-B212-74AB22DEA759"><p>Writing a parser plug-in. </p> </li>

   173 <li id="GUID-A86A66BB-0C80-5760-B7C3-7C4E276C5EFF"><p>Customising a parser

   174 plug-in. </p> </li>

   175 <li id="GUID-3F689A67-D8DC-50EF-9D49-476417E503B6"><p>Creating a resource

   176 file for a parser plug-in. </p> </li>

   177 </ul> </section>

   178 </conbody><related-links>

   179 <link href="GUID-4A9255D1-42A4-57FA-A4B4-42C552964047.dita"><linktext>XML Framework

   180 Tutorials</linktext></link>

   181 </related-links></concept>