Research Directions in Object Oriented Languages

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Research Directions in Object Oriented Languages

• Bharat Jayaraman
• Professor and Chair
• Department of Computer Science Engineering
• University at Buffalo, NY 14260
• http//www.cse.buffalo.edu/LRG

Joint work with recent PhD graduates Pallavi
Tambay (2003) and Paul Gestwicki (2005) and
several MS students at Buffalo
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Programming Languages
Imperative
Declarative
Procedural
Data Abstraction
Relational
Functional
Logic
Modules
Constraints
Objects
C
Fortran
ML

Ada
Java
CLP Prolog
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Two Research Projects

• Modeling Complex Systems
• Interactive Visualization

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I. Modeling Complex Systems

• Motivating Domains
• Engineering
• Organizational
• Biological
• Common Characteristics
• Assembly of components
• Laws of behavior
• Natural visual representations

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Building Elements
(Kalay et al 1998)
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Examples of Laws/Constraints

• The load on a wall its load bearing capacity.
• The sum of the forces at a joint should be
  zero.
• Various other constraints, such as
• - mate constraints
• - flush constraints
• - angle constraints
• etc.

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Our Principles of Modeling

• compositional specification of structure
• ? objects
• declarative specification of behavior
• ? constraints
• visual specification of assembly ? diagrams

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I. Constrained Objects

• An object is a container of data that is accessed
  via a well-defined interface of procedures.
  (Imperative)
• A constrained object contains data that is
  governed by laws, or constraints. (Declarative)
• Examples
• resistor in a circuit
• a joint in a truss
• a cell in a spreadsheet

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Constraints

• A constraint is a declarative relation among
  variables, e.g.,
• F 32 1.8C
• Constraints are additive, and collectively
  enforce the conditions among variables
• D 1
• D 31
• D 29 ? M 2 /\ leapyear(Y)
• Many algorithms for constraint satisfaction

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1. Circuits as Constrained Objects
V1 I1 R1
V2 I2 R2
V3 I3 R3
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Overview of Cob Programs

• class class_id extends class_id
• attributes
• attributes
• constraints
• constraints
• constructor
• constructor_clauses

Class inheritance
equations, inequations, conditional, quantified,
aggregate
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Cob Class Definitions
class parallel extends component attributes
component C constraints forall X in C
(X.V V) (sum X in C X.I) I (sum X
in C 1/X.R) 1/R constructor parallel(P)
C P
class component attributes Real
V, I, R constraints V I R constructor
component(V1, I1, R1) V V1 I I1
R R1
Ohms Law
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2. Truss as Constrained Object
Load
Load
Joint
Beam
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• class joint
• attributes
• bar Bars
• load Loads
• constraints
• (sum X in Bars X.B.F sin(X.A))
• (sum L in Loads L.F sin(L.A))
  0
• (sum Y in Bars Y.B.F cos(Y.A))
• (sum M in Loads M.F cos(M.A))
  0
• constructor joint(B1, L1) Bars B1 Loads
  L1

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• class bar
• attributes
• beam B real A
• constraints
• 0 ? A A ? 360
• constructor bar (B1, A1)
• B B1 A A1
• class load
• attributes
• real F, A
• constraints
• 0 ? A A ? 360
• constructor load (F1, A1)
• F F1 A A1

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class beam attributes real E, Sy, L, W,
H, F_bn, F_bk, F_t, Sigma, I, F constraints
Pi 3.141 I F_bk L L / (Pi Pi
E) I W H H H / 12 F_t Sy
W H Sigma H I F_bn / (8 I)
F F_t - F gt 0 F F_bk - F lt
0 constructor beam(E1, Sy1, L1, W1, H1,F1)
E E1 L L1 HH1 WW1 F F1
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Overall Modeling Scenario
modeling define_classes
build_instance
solve_instance
modify re_solve
query
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Modeling Tools

• Constrained Object Language (Cob)
• Text-based language
• Constraint-Based UML (CUML)
• Domain-independent graphical modeling language
• Domain-Specific Visual Programming
• Diagrammatic notations customized for specific
  application domains, e.g., circuits, trusses, etc.

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(with R. Jotwani)
CUML Constraint-based UML
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CUML ? Cob
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(with A. Dev and N. Menon)
Domain-Specific Visual Language

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(No Transcript)
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Compiled CUML Code
Compiled Circuit Diagram Code
Answers
Cob Compiler
Diagram Manager
Constraint Engine
CLP Code
Optimized Code
Optimizer
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CUML Class Diagram
Compiler
Textual Cob Code
By Chinchani, Pramanik, Dutta
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Circuit Diagram
Compiler
Textual Code
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Optimized Code (by partial evaluation of
generated code)

• V1 V2 I1 10 I2 20
• V3 V4 I3 20 I4 20
• S.I I1 I2 I3 I4
• 1/P1.R 1/10 1/ 20
• V3 S.I P2 .R
• 1/P2.R 1/20 1/20
• 30 S.I S.R
• 30 V1 V3
• S.R P1.R P2.R

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Building Elements (Kalay 1998)
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Overall Class Diagram
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Class Building

• class building
• attributes
• level Ls
• real Area
• constraints
• Area sum X in Ls X.Area
• constructor
• building(L)
• Ls L

Area of the building is the sum of areas of each
level
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Class Slab

• class slab
• attributes
• level Pl
• beam Peripheralbeams
• real Z
• constraints
• forall B in Peripheralbeams B.Z Z
• constructor
• slab(L,B)
• Pl L
• Peripheralbeams B

The height of all beams surrounding the slab must
be the same
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Two-level House (Kalay et al)
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Cob Representation for a Space

• space Spaces00
• slab Slabs0
• slab Slabs1
• surface Surfaces00
• beam Beams01
• slab Slabs00
• surface Surfaces003, Surfaces002
• surface Surfaces001, Surfaces000
• horizontalSurface Ceiling00
• horizontalSurface Floor00
• beam B014, B013,B012, B011
• edge Edge003, Edge002
• edge Edge001, Edge000
• wall Wall007, Wall002
• wall Wall001, Wall000
• column C8,C4, C6, C2
• vertex V8, V7, V6, V5
• vertex V26, V30, V36, V31
• level Level0

All the elements needed to depict Spaces00 (green)
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Cob Representation (cont)

• Wall007 new wall( V7, V8, 3.0, B014 )
• Wall002 new wall( V6, V7, 3.0, B013 )
• Wall001 new wall( V5, V6, 3.0, B012 )
• Wall000 new wall( V8, V5, 3.0, B011 )
• Slabs10 new slab( Level1, Beams10 )
• Slabs00 new slab( Level0, Beams00 )
• B012 new beam( V5, V6, B014, _ )
• B011 new beam( V8, V5, B013, _ )
• B014 new beam( V7, V8, B012, _ )
• B013 new beam( V6, V7, B011, _ )
• C4 new column( V6, V50 )
• C6 new column( V8, V51 )
• C2 new column( V5, V46 )
• C8 new column( V7, V55 )
• Edge003 new edge( Surfaces003, V7, Edge011 )
• Edge002 new edge( Surfaces002, V6, _ )
• Edge001 new edge( Surfaces001, V5, _ )
• Edge000 new edge( Surfaces000, V8, _ )
• V36 new vertex( V55, C8, 5.0, 5.0, 3.0 )

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Observations

• Constrained objects represent nicely the
  structure and constraints arising in intelligent
  building representations.
• The model described in this presentation has been
  implemented and works in a predictable way.
• The current approach, even when applied to a
  simple two-level house with five spaces, is still
  tedious and error prone.
• There is a need for a higher-level specification
  from which Cob code can be generated ?
  Component-based Design
• Inconsistency analysis and debugging are very
  important

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Conclusions and Further Work

• Constrained Objects Constraints Objects
• Applicable in many domains
• Facilitates true visual programming

• Model Analysis and Fault Detection
• Dynamic and Evolving Systems
• Intelligent Visualizations

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II. Interactive Visualization of OO Programs

• Conventional Execution Model
• data objects and procedure activations are in
  separate spaces.
• Object-Oriented Execution Model
• procedure activations occur inside data
  objects, i.e., objects are execution environments
• Several more criteria for a good visualization
  system for OOPs

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Binary Search Tree in Java

• class Tree
• public Tree(int n)
• value n
• left null
• right null
• protected int value
• protected Tree left
• protected Tree right

• public void insert(int n)
• if (value n) return
• if (value lt n)
• if (right null)
• right new Tree(n)
• else right.insert(n)
• else if (left null)
• left new Tree(n)
• else left.insert(n)

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1
Tree
Tree
2
3
Tree
5
6
7
Tree
Tree
Tree
4
Tree
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1
Tree
Tree
2
3
Tree
5
6
7
Tree
Tree
Tree
4
Tree
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i

Tree
value
int
left
Tree
i
right
Tree
Tree
Tree
const
proc
insert
j
insert
n
int
k
n
rpdl
insert in Tree
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Visualization Criteria

• Object as environments
• Multiple View of Objects
• Aesthetic Drawing
• Forward and Reverse Execution
• History of Execution
• Support Run-time Queries
• Use Existing Compiler and Run-time System

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JIVE Java Interactive Visualization Environment
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JIVE supports Source Code Highlighting, Break
Points, and Forward as well as Reverse
Stepping of Programs
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JIVE Interaction Controls
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Displaying only the Call Path
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Object Diagram without Inherited Objects
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Minimized Object Diagram
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Final Object Diagram
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Final Minimized Diagram
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• Time
• Sequence
• Diagram
• to capture
• the history
• of method
• calls between
• objects

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Tree Program with GUI front-end
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Tree Program with Graphical User Interface
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Selective Expansion of Object Diagram
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Querying the Runtime State
Runtime Query
Which variable has the value 50?
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Visual Display of Query Result
Object BST2 has the answer
Exact point of assignment
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Visual Display of Query Result
Variable V in Object BST2 has the value 50!
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Show all changes to variable left
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Concluding Remarks

• Diagrams clarify Java semantics
• handles advanced features
• Visualization environment
• pedagogic tool
• visual debugger
• JPDA is key to the implementation
• Some research issues
• Aesthetic drawing
• Efficient reverse stepping

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Current and Future Work

• Reverse execution and efficient state-saving
• Drawing algorithms
• Visual Queries
• Relationship between programs and diagrams
• Applications in Security