chapter 2.3-multimedia storage techniques
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XPath Introduction XPath is a language for finding information in an XML
document.
XPath is used to navigate through elements and attributes inan XML document.
What is XPath?
* XPath is a syntax for defining parts of an XML document* XPath uses path expressions to navigate in XML documents
* XPath contains a library of standard functions
* XPath is a major element in XSLT( EXtensible Stylesheet
Language).
* XPath is a W3C recommendation
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In XPath, there are seven kinds of nodes: element,attribute, text, namespace, processing-instruction,comment, and document (root) nodes.
Harry
Potter
J K. Rowling200529.99
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Example of nodes in the XMLdocument above:
(document node)
J K. Rowling (element node)lang="en" (attribute node)
Atomic values
Atomic values are nodes with no children or parent.Example of atomic values:J K. Rowling"en"
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Items
Items are atomic values or nodes.
Relationship of Nodes
Parent
Each element and attribute has one parent.
In the following example; the book element is the parent of the title,
author, year, and price:
Harry Potter
J K. Rowling
2005
29.99
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Children
Element nodes may have zero, one or more children.In the following example; the title, author, year, andprice elements are all children of the book element:
Harry PotterJ K. Rowling2005
29.99
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Siblings
Nodes that have the same parent.In the following example; the title, author, year, andprice elements are all siblings:
Harry PotterJ K. Rowling2005
29.99
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Ancestors
A node's parent, parent's parent, etc.In the following example; the ancestors of the titleelement are the book element and the bookstoreelement:
Harry PotterJ K. Rowling
200529.99
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Descendants
A node's children, children's children, etc.In the following example; descendants of the bookstoreelement are the book, title, author, year, and priceelements:
Harry PotterJ K. Rowling
200529.99
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XPath uses path expressions to select nodes or node-sets in an XML document.
The node is selected by following a path or steps.
Harry Potter
29.99
Learning XML
39.95
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Selecting Nodes
XPath uses path expressions to select nodes in an XML document.
The node is selected by following a path or steps. The most useful
path expressions are listed below:
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Examples
In the table below we have listed some path expressions and the result
of the expressions:
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Predicates
Predicates are used to find a specific node or a node that contains a
specific value.
Predicates are always embedded in square brackets.
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Selecting Unknown Nodes
XPath wildcards can be used to select unknown XML elements.
Selecting Several Paths
By using the | operator in an XPath expression you canselect several paths.
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Xpath Axes
In the table, we have listed some path expressions andthe result of the expressions:
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XPath Axes
An axis defines a node-set relative to the current node.
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Location Path Expression
A location path can be absolute or relative.
An absolute location path starts with a slash ( / ) and a relative location
path does not. In both cases the location path consists of one or more
steps, each separated by a slash:
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XPath Operators
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Video, Audio and the Switch Element (SMIL)
Adding video and audio media to your presentationis just as easy as adding images. The onlydifference is that we use the and tags instead of tags. These tags also take a
lot of the same attributes such as src, region, begin,dur, etc. To add some audio, or more specifically aRealMedia (.rm) file, we add this tag to our SMILdocument, . Below is what
our code should look like now.
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When it comes to video, it's just like adding anotherimage.
First, create a region to hold the video, then specify thevideo with the tag.Include the location of the video file in the src attributeof the tag.
With the tag, we can optimize the presentationto fit the user's situation. All the content tags, i.e., , , ,, , etc., have attributes that you use along
with such as system-screen-size, system-bitrateand system-language. The SMIL parser then selects themedia that best suits the user's needs using theseattributes.
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What this does is chooses only one tag to use based on the user's bitrate. For example, if someone views this SMIL
presentation with a 28kbps modem, they'll get the "moo-28k.rm" file. On the other hand, if someone views it with something else not
specified, they'll get the "moo-other.rm" file since that has no "system-bitrate" attribute and is deemed the default.
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Metadata Processing Steps for Lecture Archive
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illustrates the metadata processing and generation components for this
application.
Spatial Layout for a Simple SMIL Example
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Spatial Layout for a Simple SMIL Example
Replay Interface for a SMIL Presentation Lecture
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Replay Interface for a SMIL Presentation Lecture
P t ti C t
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Presentation Capture
1. Filming a lecturer giving a PowerPoint
presentation;2. Digitizing and encoding the video footage to
MPEG format (for analysis) and RealMedia
format (for streaming);
3. Analysing the digitized footage or logging datato determine the times at which slide changes
occur;
4. Using the temporal information to generate a
SMIL presentation which integrates synchronized
digital video and PowerPoint slides with a timeline
for browsing and jumping directly to a particular
slide.
Overview of System Components and Process Flow
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Ove v ew o Syste Co po e ts a d ocess ow
PresentationIndexer application
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PresentationIndexer application.
Presentation Archive Search
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Presentation Browse and Replay Interface
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p y