Constraint%20Animation%20Using%20an%20Object-Oriented%20Declarative%20Language

1
Constraint Animation Using an Object-Oriented
Declarative Language

• Jeff Gray and Stephen Schach
• Vanderbilt University
• jgray, srs_at_vuse.vanderbilt.edu
• ACM Southeast Conference 2000
• April 7-8, 2000
• Clemson, SC

2
Overview

• Problem Motivation
• Specification Animation
• UML/OCL
• Prolog
• Mapping UML/OCL to Prolog
• Example
• Using the Intelligence Server to construct a
  simple animation environment
• Ideas for Improvement

3
Problem Motivation

• Fact Our words are pregnant with meaning
• Oxford English Dictionary
• 500 words used most have an average of 23
  meanings
• set has 430 different meanings 25 pgs. and 60k
  words
• The Resulting Problem Ambiguity
• Humorous statements
• Military disasters (Tennysons poem on Crimean
  War)
• Large Software Requirements Specification
• Other Problems Inconsistency Confusing
  Verbiage

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An Example

• The Landing Pilot is the Non-Handling Pilot
  until the decision altitude call, when the
  Handling Non-Landing Pilot hands the handling to
  the Non-Handling Landing Pilot, unless the latter
  calls go around, in which case the Handling
  Non-Landing Pilot continues handling and the
  Non-Handling Landing Pilot continues non-handling
  until the next call of land or go around as
  appropriate. In view of recent confusions over
  these rules, it was deemed necessary to restate
  them clearly.
• British Airways Memorandum, quoted in Pilot
  Magazine, December 1996.

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Natural Language Problem

• The Humpty-Dumpty Syndrome

• When I use a word, Humpty Dumpty said, in a
  rather scornful tone,
• it means just what I choose it to mean - nothing
  more nor less.
• The question is, said Alice,
• whether you can make words mean so many
  different things.
• 
  Lewis Carroll

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Collection of Ambiguous or Inconsistent/Incomplet
e Statements

• I will bring my bike tomorrow if it looks nice
  in the morning
• I found a smoldering cigarette left by a horse
• Check it out
• http//www.vuse.vanderbilt.edu/jgray/ambig.html

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Levels of Formalism

• Categories of formalism
• Informal natural language
• Semi-formal notations
• Formal specification languages

Informal
Familiarity
Semi-formal
Formal
Mathematical Rigor
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Levels of Formalism

• Semi-formal specifications lack the formality for
  rigorous mathematical verification
• Formal specifications are not customer friendly
• This returns us to the underlying tension in
  the software process that between the subjective
  and the objective, between the holistic mental
  view and the rigorous formal model. The first
  describes what is needed the second ensures that
  what was requested is delivered.
• Blum, Bruce, A Taxonomy of Software Development
  Methods, Communications of the ACM, vol. 37, no.
  11, November 1994, pp. 82?94.

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Graphical Notations

• Petre, Marian, Why Looking Isnt Always Seeing
  Readership Skills and Graphical Programming,
  Communications of the ACM, June 1995, pp. 33?44.

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UML/OCL

• Enriching a UML diagram with OCL constraints can
  aid in improving the common understanding of the
  underlying model (natural language is not used to
  describe the effect of the constraint)
• Several groups are working hard to rigorously
  define the UML semantics using formal languages
  (The Precise UML Group) several workshops
  exist
• A rigorous semantics would permit a type of
  executable specification to be performed

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Specification Animation

• Offers a type of throw-away prototype resulting
  from an executable specification
• Can aid in making the underlying formalism
  transparent to end-user
• Wide body of literature
• Debate between tradeoff of expressiveness with
  the speed of executability
• Most efforts focus on animating Z
• Declarative programming languages are often used
  to aid in the mapping from the specification(Prol
  og is the language used with most frequency)

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Prolog

• Vendor Logic Programming Associates
• Combines the declarative power and inference
  engine of Prolog with the benefits of OOP
• Supports
• structural organization of Prolog predicates in
  classes
• single/group of messages can be sent to
  single/group of objects
• data driven programming - allows daemons to be
  attached to crucial events (construction/destructi
  on, value changes)
• multiple inheritance and polymorphism
• Drawback Very primitive environment costly

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Mapping UML/OCL to Prolog

• UML class diagrams provide
• the corresponding class structure for the
  Prolog code
• attributes/types and method names for Prolog
  code
• aggregation/relations that must be Prolog parts
• Many OCL collection operations have direct
  mappings to Prolog predicates (we get these
  free!)
• OCL forall can often be mapped to Prolog all
  instance
• OCL select -gt all instance sucthat...
• An important asset is a library of Prolog
  predicates that emulate standard OCL operations
• e.g., oclIsTypeOf, oclType, oclIsKindOf, size

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Mapping UML/OCL to Prolog

• oclIsTypeOf
• A reflective class attribute must be defined,
  e.g.
• class attributes
• class_type outputPort.
• operator then defined in Prolog as
• oclIsTypeOf(AType) - self_at_class_type AType.
• size
• A class attribute called size_att must be defined
  for each class
• Define a simple library function to increment
  size_att
• size_func - size_att 1.
• Generic size is then defined as
• size(S) - size_att 0, (all instance
  class) lt- size_func, S _at_size_att.

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Example
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Example Constraint 1

• It is invalid to connect an input port to another
  input port, or an output port to another output
  port
• In OCL, this can expressed as
  Connection-gtforAll(c
  c.src.oclIsTypeOf(OutputPort) and
  c.dst.oclIsTypeOf(InputPort))
• In Prolog inv_Connection - (all
  instance class)lt- (_at_srclt-oclIsTypeOf(
  'outputPort'), _at_dstlt-oclIsTypeOf(in
  putPort)).

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Example Constraint 2

• Microphones can only connect to preamps preamp
  outputs can only connect to poweramps poweramp
  outputs only to speakers
• In OCL, this can expressed as (Microphone-gtPreamp)
  Mic-gtforAll(m
  
  m.OutputPort.dst.oclIsTypeOf(PreAmp))
• In Prolog inv_Mic_Dst - (all
  instance class)lt-(outputPort_at_dstlt-
  oclIsTypeOf(preAmp')).

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Example Constraint 3

• At least one poweramp must exist in an audio
  system
• In OCL, this can expressed as (Microphone-gtPreamp)
  PowerAmp.allInstances-gtsize gt 1.
  
• In Prolog inv_powerAmp_existence -
  size(S), S gt 1.

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Using the Intelligence Server
Developers
Customer
Animation Environment
Result
Query
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Intelligence Server
Win-Prolog
Intelligence Server
Front End
Server.OVL
Server.DLL
PRO386W.EXE(runtime kernel)
Server.PC
User definedProlog code
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Intelligence Server

• Six Interface Functions of Server.DLL
• LoadProlog
• initialize/configure WinProlog
• HaltProlog
• shut down WinProlog
• InitGoal
• initialize a Prolog goal
• CallGoal
• call previous goal, return solution, backtrack
• ExitGoal
• exit a goal once solutions are no longer needed
• TellGoal
• send textual info back to a goal that requires
  input

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Intelligence Server
Win-Prolog
Intelligence Server
Front End
Server.OVL
Server.DLL
PRO386W.EXE(runtime kernel)
Server.PC
User definedProlog code
Animation Environment
Translated OCL
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Simple Animation Environment
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Other Related Applications
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Ideas for Improvement

• Current work is very primitive - core functions
  of an animator are still needed
• Automated Mapping to Prolog
• Retrieve model from Rose (using COM)
• Build on current OCL parsers
• Incorporate Interaction (Sequence) Diagrams
• an existing sequence diagram can be used as an
  example script to drive an animation session
• the interactions among objects in an animation
  session could be captured to construct a sequence
  diagram
• Support for pre/post-conditions