Timed Petri Net Representation of the SMIL of XML

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Timed Petri Net Representation of the SMIL of XML

• Chung, S.M. Pereira, A.L.
• Wright State University, Dayton, Ohio, USA
• Information Technology Computers and
  Communications, 2003. Proceedings. ITCC 2003.
  International Conference on , 2003
• Speaker C.W. Tien 2003/05/06

2
Abstract

• Propose a technique by which clients can submit
  to the server information of all the required
  multimedia objects and their temporal
  relationships for presentation.
• The technique uses an enhanced Timed Petri Net
  (TPN) to capture information of multimedia
  objects along with their timing and
  synchronization specified in the SMIL.
• Display a graphical representation of the
  temporal and synchronization information captured
  by the data structure representing the Timed
  Petri Net.
• This information can be used by a multimedia
  server to schedule and optimize the delivery of
  multimedia data streams.

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Outline

• 1. Introduction
• 2. Parsing SMIL into a TPN
• 2.1. SMIL
• 2.2. Petri Nets
• 2.3. A New Timed Petri Net
• 2.4. Capturing SMIL Semantics
• 3. Graphical Display of the Timed Petri Net
  Representation of SMIL
• 4. Conclusion

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2.2. Petri Nets

• The basic Petri net structure is composed of four
  parts a set of places P, a set of transitions T,
  an input function I and an output function O.
• The input and output functions relate transitions
  and places

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2.2. Petri Nets

• A circle represents a place
• A bar represents a transition.
• Directed arcs connect the places to the
  transitions and from transitions to places.
• An arc directed from a place to a transition
  defines the place to be an input of the
  transition.
• An output place is indicated by an arc from the
  transition to the place.

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2.2. Petri Nets

• A marked Petri net includes a marking M which
  assigns tokens to each place
• Tokens are represented by dots in the Petri net
  graph.
• Tokens are used to define the execution of a
  Petri net.
• The number of tokens that may be assigned to a
  place is unbounded

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2.2. Petri Nets

• In simple Petri nets, firing of a transition is
  assumed to be instantaneous.
• A class of enhanced Petri net models have been
  developed which assign a firing duration to each
  transition.
• These models are generally called Timed Petri Net
  (TPN) models.
• Another TPN model represents processes by places
  instead of transitions.
• Nonnegative times are assigned to each place in
  the net.
• Object Composition Petri Net (OCPN)

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2.2. Petri Nets

• An OCPN is defined as follows
• COCPN T, P, A, M, D, R where
• T t1, t2, , tm,
• P p1, p2 , pn,
• A T P U P T --gtI, I 1, 2, ,
• M P --gtL, L 0, 1, 2, ,
• D P --gtreal numbers, and
• R P --gtr1, r2, .

• T represents a set of transitions (bars).
• P represents a set of places (circles).
• A represents a set of directed arcs.
• M is a marking that represents a mapping from the
  set of places to the integers.
• D is a mapping from the set of places to the real
  numbers (durations).
• R is a mapping from the set of places to a set of
  resources.

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2.2. Petri Nets

• Firing rules
• A transition fires immediately when each of its
  input places contain an unlocked token.
• Upon Firing, the transition removes a token to
  each of its output places.
• After receiving a token, a place remains in the
  active state for the interval specified by the
  duration. During this interval the token is
  locked. When the place becomes inactive or the
  duration expires, the token becomes unlocked

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2.3. A New Time Petri Net

• The OCPN is not powerful enough to capture all
  the timing and synchronization semantics of SMIL.
  
• The OCPN cannot support the endsync attribute
  because a single place unlocking its token cannot
  fire the transition if there are other places
  with locked tokens feeding into the same
  transition.

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2.3. A New Time Petri Net

• The ltexclgt container allows only a single stream
  among a parallel group of streams to be active.
• This cannot be allowed by the OCPN because a
  transition removes a token to each of its output
  places upon firing, and after receiving a token,
  a place remains in the active state for the
  interval specified by the duration.

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2.3. A New Time Petri Net

• The ltpriorityClassgt container, when used within
  an ltexclgt container, specifies the behavior of an
  active stream when another stream starts up
  within the same ltexclgt container.
• The semantics of this element also is not
  supported by the OCPN.

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2.3. A New Time Petri Net

• Each place can be assigned tokens of three
  distinct types type 0, type 1, type 2
• A single token within a place represents a token
  controlling the firing of a transition.
• If there are two tokens in a place, then the
  upper one controls the state of the place and the
  lower one controls the firing of the transition.

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2.3. A New Time Petri Net

• The allocation of tokens that control the firing
  of a transition is done initially in the TPN.
• A place is inactive in the absence of a token
  that determines its state
• Tokens can be unlocked at a place only if both
  tokens are present at that place.
• Only the unlocking of the token which controls
  the firing of the transition will have an effect
  on the transitions firing.

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2.3. A New Time Petri Net

• There are two types of transitions the ordinary
  transition and the special transition.
• Both transition types have associated values that
  specify the number of times a transition can
  fire.

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2.3. A New Time Petri Net

• Fire rules
• An ordinary transition fires in two cases
• If each of its input places contains an unlocked
  token of type 0. This is the default behavior of
  a group of media streams in parallel.
• If one or more of its input places contain an
  unlocked token but only if the token is of type
  1.

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2.3. A New Time Petri Net

• Fire rules
• A special transition fires in two cases
• If one of its input places contains an unlocked
  token of type 2 and the rest of its input places
  contain an unlocked token of type 0.
• If one of its input places contain an unlocked
  token of type 2 and one or more of its other
  input places contain an unlocked token of type 1.

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2.3. A New Time Petri Net

• Fire rules
• Upon firing, an ordinary transition removes a
  token of type 0 to each of its output places.
• Upon firing, a special transition removes a token
  of type 0 to only one of its output places and
  tokens of type 1 to all of its other output
  places.

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2.3. A New Time Petri Net

• Fire rules
• If an output place receives a token of type 1,
  then the place will remain inactive or will be
  deactivated if it is already active.
• If the output place receives a token of type 0
  then it will remain active for the duration
  specified or until it is deactivated.

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2.3. A New Time Petri Net
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2.3. A New Time Petri Net
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2.3. A New Time Petri Net

• The proposed TPN is defined as follows
• CTPN OST, P, A, X, Y, U, W, D, R where
• OST ot1, ot2, , otm U st1, st2, , stn,
• P p1, p2 , pk,
• A OST P U P OST --gt I, I 1, 2, ,
• X P --gt H, H h1, h2, , hj,
• Y H --gt L1 U L2 U L3, L1 0, 3, 6, , L2
  1, 4, 7, , L2 2, 5, 8, ,
• U OST --gt V, V v1, v2, ,
• W V --gt L, L 0, 1, 2, ,
• D P --gt  real numbers, and
• R P --gt  r1, r2,

• OST represent a set of ordinary transitions
  (bars) and special transitions (vertical dashed
  lines).
• P represent a set of places (circles).
• A represent a set of directed arcs.
• X is a mapping from the set of places to a set of
  token holders.
• Y is a mapping from the set of token holders to
  the integers.
• U is a mapping from the set of transitions to a
  set of values.
• W is a mapping from the set of values to the
  integers.
• D is a mapping from the set of places to the real
  numbers (durations).
• R is a mapping from the set of places to a set of
  resources.

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2.4. Capturing SMIL Semantics

• In the TPN data structure,
• each place is represented by a single place node,
  and
• The place node contains fields for resources,
  durations, token holders and a pointer to a
  transition node.
• each transition is represented by a list having
  one or more transition nodes.
• A transition node contains fields for values, a
  pointer to a place node, and a pointer to a
  transition node.
• The values are used to control the firing of the
  transition, to indicate the number of times it
  can fire, and to indicate its type.

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2.4. Capturing SMIL Semantics

• ltseqgt
• ltaudio src"audio.wav" end"10s"/gt
• ltvideo src"video.mpg" begin"2s"/gt
• lt/seqgt

• The information of timing attributes and media
  object URIs is captured within places.
• For the begin and end attributes, a duration is
  modeled by using arcs and a place which possesses
  null resources and a finite duration.
• An event specified for the begin and end
  attributes is modeled by using arcs and a place
  which possesses a resource representing an event
  and zero duration.
• In the case of the end attribute, a token of type
  1 is initially allocated to the place to control
  the firing of the transition.

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2.4. Capturing SMIL Semantics

• For the endsync attribute within a ltpargt
  container,
• all the children are initially allocated a token
  of type 1 if the group has to end with the first
  stream that stops play back.
• If the parallel group has to end with a
  particular child, then only that child is
  initially allocated a token of type 1.
• In case of the default semantics of ltpargt, the
  tokens initially allocated to the children are of
  type 0.

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2.4. Capturing SMIL Semantics

• The transition representing the beginning of the
  children within an ltexclgt container is tied into
  the occurrence of certain event.
• When an event occurs, only the particular child
  to be played will be passed a token of type 1.
• On the event that another stream needs to be
  started up, then only the required stream
  receives a token of type 1 and the child that has
  been active will receive a token of type 0.

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3. Graphical Display of the Timed Petri Net
Representation of SMIL

• Implementation environment UNIX
• Tools fast lexical analyzer generator (flex) is
  used for the lexical analysis and Bison for
  parsing.
• Data structure
• The graphical display is done by recursively
  traversing the TPN data structure and using
  OpenGL to draw on the screen.

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• ltseqgt
• ltimg src"image1.jpg" dur"5s"/gt
• ltpar endsync"first"gt
• ltaudio src"audio1.wav" begin"3s" dur"35s"/gt
• ltseqgt
• lttext src"text1.html" begin"0s"
  end"stopbutton.click"/gt
• lttext src"text2.html" dur"10s"/gt
• lt/seqgt
• ltvideo src"video1.mpg" begin"7s" dur"30s"
  fill"freeze"/gt
• lt/pargt
• ltimg src"image2.jpg" dur"10s"/gt
• lt/seqgt

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• ltpargt
• ltseqgt
• ltimg src"image1.jpg" begin"5s" dur"5s"/gt
• ltaudio src"audio1.wav" dur"20s"/gt
• ltexclgt
• ltvideo src"video1.mpg" begin"0s" dur"20s"/gt
• ltaudio src"audio2.wav" begin"10s" dur"15s"/gt
• lt/exclgt
• lt/seqgt
• ltimg src"image2.jpg" id"img2" end"30s"/gt
• ltaudio src"audio3.wav" end"img2.end"/gt
• lt/pargt

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• ltpargt
• ltpargt
• ltimg src"image1.jpg" idimg1 begin"5s"
  dur"5s"/gt
• ltvideo srcvideo1.mpg" idvid1 dur"20s"/gt
• ltexclgt
• ltimg srcimage2.jpg" beginimg1.activateEvent"
  dur"20s"/gt
• ltvideo srcvideo2.mpg" beginvid1.activateEvent"
  dur"15s"/gt
• lt/exclgt
• lt/pargt
• ltimg src"image3.jpg" id"img3" end"30s"/gt
• ltvideo srcvideo3.mpg" end"img3.end"/gt
• ltseqgt
• ltimg src"image4.jpg" endimg3.activateEvent"/gt
• ltvideo srcvideo4.mpg" repeatCount3"/gt
• lt/seqgt
• lt/pargt

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3. Graphical Display of the Timed Petri Net
Representation of SMIL

• Labels meanings
• The letters V, A, I and T indicate the type of
  media object
• The numbers are printed in ascending order from
  left to right for objects in a sequence, and top
  to bottom for objects in parallel.
• A label above a vertical line is an index to
  additional semantic information about the child
  elements in parallel.
• A solid vertical line indicates that the child
  elements are specified within a ltpargt container
• A dashed vertical line indicates that the child
  elements are specified within a ltexclgt container.

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4. Conclusion

• Proposed a new technique in which a client can
  inform the multimedia server of all the temporal
  and synchronization requirements of the
  multimedia data required for presentation.
• The client can specify its requirements in a SMIL
  document.
• The multimedia server can parse the SMIL document
  into a Timed Petri Net (TPN).
• The multimedia server can use the TPN to optimize
  its delivery schedule and best utilize the system
  resources
• The proposed TPN is an enhancement of the Object
  Composition Petri Net (OCPN).
• The TPN can capture the temporal synchronization
  semantics supported by SMIL.