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<concept id="GUID-FDC0004A-A2EE-5B73-9E2D-B6864C600AF9" xml:lang="en"><title>SMIL

Parser Overview</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The SMIL Parser component uses XML DOM to validate SMIL (Synchronized Multimedia

Integration Language) documents for rendering MMS (Multimedia Message Service)

messages. </p>

<section id="GUID-0EDFED36-1728-48D0-AC92-D269E0568DC9"><title>Purpose</title> <p>Its

primary purpose is to provide SMIL parsing and composing functionality for

MMS. However, the component has also been designed to provide support for

parsing and composing other types of XML document, for example XHTML. </p> </section>

<section id="GUID-17D17217-ECD7-49C8-87CE-8505B423727A"><title>Architecture</title> <p>The

SMIL Parser component comprises of the following elements: </p> <ul>

<li id="GUID-299AA6C3-B517-5CAB-95BC-11E36D805941"><p>A generic set of classes

that can represent the contents of an XML file in an object hierarchy for

efficient processing. These classes are referred to as the Mini-DOM, because

they use some but not all concepts from the DOM (Document Object Model). The

classes can perform syntax checking and validation with regard to a specific

DTD set at run time. </p> </li>

<li id="GUID-C4FCE7B0-3B24-514D-8D92-B089FBA0CE16"><p>An interface class that

defines the signature for the necessary DTD validation functions. Any DTD-specific

validation class is derived from this, and provides an implementation of these

functions. </p> </li>

<li id="GUID-C26FE2C2-3FDD-5347-909E-86BDD1E003A1"><p>A parser that can read

an XML file and can generate Mini-DOM objects. </p> </li>

<li id="GUID-918807C2-FBFB-501D-8388-720834F627B2"><p>A composer that can

take a Mini-DOM object tree and output an XML file. </p> </li>

</ul> <fig id="GUID-3B925574-105C-5EA3-94A8-CFCED0D0F544">

<title>              SMIL Parser architecture            </title>

</fig> <p>The following sections gives detailed explanation of the above elements: </p> <p><b>XML

Mini-DOM </b> </p> <p>The XML Mini-DOM classes are based on a subset of the

DOM classes. The Mini-DOM is a subset, because it is not intended to support

some of the more ambitious or obscure uses of XML. It also discards some of

the theoretical layers. For example, attributes are not created as separate

nodes, but are member data of element objects. The Mini-DOM is not intended

as a porting API whereby applications written on other platforms using the

DOM can be trivially ported to the Symbian platform. </p> <p>When

an XML file is parsed, and a Mini-DOM tree is created, the Mini-DOM classes

provide an API to navigate through the document objects and to query the element

attributes. When an XML file is to be composed, the Mini-DOM provides an API

to inquiry the elements allowing the XML Composer to produce a textual representation. </p> <p><b>SMIL

DTD</b> </p> <p>SMIL DTD allows a Mini-DOM tree to be validated for a specific

DTD. A DTD interface class <xref href="GUID-F294DC1C-D762-3CF7-BB64-18E742BA6EAA.dita"><apiname>MXMLDtd</apiname></xref> is defined from which

specific DTD classes are derived. The Mini-DOM can then call DTD-specific

functions through implementations of the interface. </p> <p><b>XML Parser</b> </p> <p>XML

Parser is a single-pass parser with a two-stage pipeline. The first stage

is basic lexical analysis that reads the data from a source, performs some

housekeeping and normalization functions on it, and passes on meaningful sections

of text to the second stage for parsing. </p> <p>The following operations

are performed on the input in the lexical analysis stage: </p> <ul>

<li id="GUID-EF082699-6424-5F34-A3F9-BE64DE2CDFB7"><p>Comments are stripped

out. </p> </li>

<li id="GUID-BCC33D81-F26C-5F76-9EA9-D37B725A9EEA"><p>Processing instructions

are stripped out. </p> </li>

</ul> <p>The following are the meaningful sections of text: </p> <ul>

<li id="GUID-9CB81940-2E24-568C-8377-761CE85B6490"><p>Complete tag definitions

(for example, start tag, end tag or combined tag) </p> </li>

<li id="GUID-666F1557-907C-541B-8453-2CFD523036DD"><p>Sections of text of

specific CDATA sections </p> </li>

</ul> <p>The second stage is to parse elements by breaking out the element

name and sequence of attribute values and creating generic attributes. </p> <p>Built-in

character entities are replaced by their values if they have previously been

defined. Any entity references that are not recognized are left untouched. </p> <p>The

second parser stage creates DOM objects in a tree structure by adding new

elements onto the child element list of each element. Encountering a start

tag causes an element to be created under the then-current element, while

encountering an end tag causes the then-current element to move up the object

tree. At the same time, the end tag is compared with the relevant element

to ensure that start and end tags match. If an empty element tag is encountered,

then the element is created, but the position for insertion of the next tag

is not descend the object tree. </p> <p>XML Parser is a generic parser and

has no specific functionality to any particular DTD. Instead, validation and

syntax checking is done through the Mini-DOM API. </p> <p>The parser carries

out the act of parsing an XML file as an active object. A single activation

of the object parses the whole file. </p> <p>The parser takes input from a

file or a buffer. Supported character sets are UTF-8 (of which ASCII is a

subset) and UTF-16. Any data not beginning with a DOM is treated as UTF-8.

The data is parsed and added to a DOM based structure. </p> <p><b>XML Composer</b> </p> <p>XML

Composer takes a DOM tree and produces an XML file representing the data in

that DOM tree. It performs a tree walk for each element, and using the generic

element API, it accesses element details and outputs the text of the elements

or the character data. </p> <p>During the tree-walk, elements that are not

empty result in a start tag and an end tag being output. Empty elements result

in a single tag being output. Instances of characters that must be replaced

by built-in entity references are also replaced. </p> <p>When an XML file

is parsed, and the resulting object tree passed into the composer, an output

file is created. The output file may not be necessarily identical to the input

file: that is, comments may be lost, and white space elements may be affected

as well. </p> </section>

<section id="GUID-18BC11E3-23B6-4356-A255-12D824D1B454"><title>APIs</title> <p>The

following are the important XML DOM APIs provided by the SMIL Parser component: </p> <table id="GUID-84248E72-234B-5487-A049-DB1D9A9B1A9A">

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

<thead>

<row>

<entry>API</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

<entry><p> <xref href="GUID-DF432AB6-7895-30E8-9B4B-378E61A7A901.dita"><apiname>CMDXMLElement</apiname></xref>  </p> </entry>

<entry><p>Provides access to element data including attribute name/value pairs. </p> <p>Attribute

access is by name. For example, to get the value of the <codeph>width</codeph> attribute,

call <xref href="GUID-68E71051-2A4D-311D-8554-14442D098560.dita"><apiname>GetAttributeL()</apiname></xref> and the value is returned as another

string. </p> <p>DTD element classes are not necessary. All elements are constructed

from the generic element class and has the following functionality: </p> <ul>

<li id="GUID-E46CBA23-1D24-574A-B450-C420F83832E1"><p>The element class has

member variables created for each element attribute defined. Each member variable

has standard accessor and mutator functions defined. </p> </li>

<li id="GUID-5654E630-FF29-5883-A8E1-16E064FEE064"><p>Validation of attribute

values can be carried out by calling <xref href="GUID-AE599A9F-7E71-3082-8118-ACA87E3E4145.dita"><apiname>IsValidAttributeForElementL()</apiname></xref>.

DTD specific validation is done based on the <xref href="GUID-F294DC1C-D762-3CF7-BB64-18E742BA6EAA.dita"><apiname>MXMLDtd</apiname></xref> object

passed to the document during creation. </p> </li>

<li id="GUID-FCFE73E0-3D5D-5056-BDE3-2BED4E3F3C47"><p>The element class has

the <xref href="GUID-21F01EDE-1C79-34AD-AF6B-5944B324539D.dita"><apiname>CheckChildren()</apiname></xref> function created to check that any

child elements conform in type and order to the requirements of the DTD. This

is achieved by calling <xref href="GUID-11DC3525-A8AD-33DE-AFEB-ED840469357F.dita"><apiname>CheckValidChildren()</apiname></xref> on the DTD

object owned by the document. </p> </li>

</ul> </entry>

</row>

<row>

<entry><p> <xref href="GUID-3AF26F84-F4C0-312D-9ABD-1C6EC0BD1675.dita"><apiname>CMDXMLParser</apiname></xref>  </p> </entry>

<entry><p>Provides functions to read an XML file and can generate Mini-DOM

objects. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-2A597821-BF7F-379A-A32C-99CF9B5CDFAA.dita"><apiname>CMDXMLDocument</apiname></xref>  </p> </entry>

<entry><p>It is an XML document with a reference to an <xref href="GUID-F294DC1C-D762-3CF7-BB64-18E742BA6EAA.dita"><apiname>MXMLDtd</apiname></xref> object. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-F294DC1C-D762-3CF7-BB64-18E742BA6EAA.dita"><apiname>MXMLDtd</apiname></xref>  </p> </entry>

<entry><p>Defines the signature for the necessary DTD validation functions.

DTD-specific validation class is derived from this and provides an implementation

of these functions. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-8BBCB6A5-A133-3BDD-8614-E5E2F1FED7E5.dita"><apiname>CMDXMLNode</apiname></xref>  </p> </entry>

<entry><p>Provides functions to store the node type and name and manages a

list of child nodes. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-78751199-C2AA-37C4-970B-191C4D496AAA.dita"><apiname>CMDXMLComposer</apiname></xref>  </p> </entry>

<entry><p>Provides functions to compose a Mini-DOM object tree and output

an XML file. </p> </entry>

</row>

</tbody>

</tgroup>

</table> </section>

<section id="GUID-42B978B7-C272-401C-9A19-E65EFE34E825"><title>Typical uses</title> <ul>

<li id="GUID-4E0FFD17-4A47-5CEC-B1C5-42CBF9FA0108"><p><xref href="GUID-2468D736-9F95-5412-B687-765D630651C7.dita">Parsing

XML Data</xref>  </p> </li>

<li id="GUID-ADCD2234-95B0-5959-AFC2-E11F17799AF0"><p><xref href="GUID-99CC6D00-DC3E-51C2-8152-060FB80F5FCD.dita">Composing

XML Data</xref>  </p> </li>

</ul> </section>

<section id="GUID-D599779A-17A9-4D12-B7BE-29909F782083"><title>See also</title> <p> <xref href="http://www.w3.org/TR/REC-DOM-Level-1/" scope="external">Document Object

Model Specification</xref>  </p> </section>

</conbody></concept>