Action Rules for Programming Constraint Propagators and Interactive User Interfaces

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Action Rules for Programming Constraint
Propagators and Interactive User Interfaces

• Neng-Fa Zhou
• CUNY Brooklyn College GC
• zhou_at_sci.brooklyn.cuny.edu
• www.sci.brooklyn.cuny.edu/zhou

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Outline of Talk

• Motivation
• Action Rules
• Programming Constraint Propagators(www.sci.brookl
  yn.cuny.edu/zhou/papers/arule.ps)
• CGLIB Constraint-based Graphics
  Library(www.sci.brooklyn.cuny.edu/zhou/papers/ac
  mdoc01.pdf)
• Demo of B-Prolog v.6
• (www.probp.com)

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Motivation

• The need for a language for programming reactive
  systems
• Constraint propagators
• Event handling
• Concurrency
• Interactive user interfaces
• Agents

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Action Rule

• Syntax

Agent, ConditionSeq, EventSet gt ActionSeq

• Operational semantics
• An agent (sub-goal) C will be suspended if
• C matches Agent,
• ConditionSeq is met, and
• EventSet is not empty
• C is activated whenever an event in EventSet is
  posted
• ActionSeq is executed when C is activated and
  ConditionSeq is met
• C is suspended again after ActionSeq is executed
• The next rule is tried if ConditionSeq fails
• C fails if ActionSeq fails

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Posting Eventspost(E)

• event(X,O)
• X suspension variable
• O event object
• Events for programming propagators
• ins(X) X is instantiated
• Events for graphics programming
• actionPerformed(O) action performed on O

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Example 1An Echoing Agent
echo_agent(X), event(X,Message) gt
write(Message),nl.
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Example 2freeze(X,G)
freeze(X,G), var(X), ins(X) gt
true. freeze(X,G) gt call(G).
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Programming Constraint Propagators

• Action rules are expressive
• Propagators for maintaining node, interval, arc
  consistency
• Propagators for global constraints
• Action rules are efficient
• B-Prolog is competitive with Ilog solver and
  GNU-Prolog

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Constraint Propagation
X Y1 (X,Y in 1..5)
Algorithm Change Propagation
Node consistency X3 X 3, Y 2 Interval
consistency generated X in 2..5, Y in 1..4 5
notin X X in 2..4, Y in 1..3 Arc
consistency 4 notin X X in 2,3,5, Y in 1,2,4
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Events for Programming Propagators

• ins(X)
• X is instantiated
• minmax(X)
• The bound of X is updated
• dom(X,E)
• An inner element E has been excluded from X

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Propagators for aXbYc

• Forward checking

'aXbYc_forward'(A,X,B,Y,C),var(X),var(Y), ins(
X),ins(Y) gt true. 'aXbYc_forward'(A,X,B,Y,
C),var(X) gt T is BYC,Ex is T//A,
(AExT-gtX Ex true). 'aXbYc_forward'(
A,X,B,Y,C) gt T is AX-C, Ey is T//B,
(BEyT-gtY is Eytrue).
When either X or Y is instantiated, instantiate
the other variable.
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Propagators for aXbYc

• Interval consistency

'aX in bYc_interval'(A,X,B,Y,C),var(X),var(Y),
minmax(Y) gt 'aX in
bYc_reduce_domain'(A,X,B,Y,C). 'aX in
bYc_interval'(A,X,B,Y,C) gt true.
Whenever the bound of Ys domain is
updated, reduce Xs domain to achieve interval
consistency.
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Propagators for aXbYc

• Arc consistency

'aX in bYc_arc'(A,X,B,Y,C),var(X),var(Y), dom(
Y,Ey) gt T is BEyC,
Ex is T//A, (AExT -gt
exclude(X,Ex)true). 'aX in
bYc_arc'(A,X,B,Y,C) gt true.
When an element Ey is excluded from Ys
domain, exclude Eys counterpart Ex from Xs
domain.
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Propagator for A1X1...AnXnC 0
'A1X1...AnXnC0'(C,A1,A2,...,An,X1,X2,..,Xn)
, n_vars_gt(n,2), ins(X1),minmax(X1),...,ins(Xn
),minmax(Xn) gt reduce domains of
X1,..,Xn to achieve ic. 'A1X1...AnXnC0'(
C,A1,A2,...,An,X1,X2,..,Xn) gt
nary_to_binary(NewC,B1,B2,Y1,Y2),
call_binary_propagator(NewC,B1,Y1,B2,Y2).
When the constraint has more than 2
variables, achieve interval consistency. When
the constraint is binary archive arc consistency.
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Performance Evaluation
Fast
B-Prolog Ilog GNU-Prolog
1
2
CHIP
Eclipse Sicstus Mozart Oz
4
Slow
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CGLIB --A Constraint-based Graphics Library

• Features
• Use constraints to specify the layouts of objects
• Use action rules to specify interactions
• Implementation
• Implemented in B-Prolog, Java, and C
• Applications
• Drawing editors, interactive user interfaces,
  document authoring, animation, information
  visualization, intelligent agents, and games.

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An Illustrative Example
go- cgButton(B), (1)
Btext Hello World!, (2) handleButtonClick(
B), (3) cgShow(B). (4)   handleButtonClick(B
), (5) actionPerformed(B) (6) gt
(7) halt. (8)
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Objects

• cgButton(X)
• Create a button X
• cgButton(X1,,Xn)
• Create a list of buttons

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Attributes of Objects
B is a button

• Base

• Derivative

y
Bwindow Bx By Bwidth Bheight Btext
Bcolor Bfont
BrightX BbottomY BcenterX BcenterY BleftTopPo
int BleftBottomPoint BrightTopPoint BrightBotto
mPoint Bcenter
x
height
width
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Constraints

• Arithmetic constraints
• O1x O1width//2 O2x
• O1centerX O2x
• Positioning constraints
• cgLeft(O1,O2)
• Same property constraints
• cgSame(O1,O2,size)
• cgSame(O1,O2,width,100)

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Constraints (Cont.)

• Grid constraints

cgGrid(_, S1,_, S2,S3,S4,
_,S5,_)
cgGrid(Bc,Bdiv,Bmul,Bsub, B7,B8, B9,
Badd, B4,B5, B6, Badd, B1,B2, B3,
Beq, B0,B0, Bdot,Beq,1,1),
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Constraints (Cont.)

• Table constraints

cgTable(Larc,Arc,Button,Lbutton,
Lcheckbox, Checkbox, Choice, Lchoice,
Lcircle,Circle,Image,Limage,
Llabel,Label,Line,Lline,
Llist,List,Oval,Loval,
Lrrectangle,Rrectangle,Rectangle,Lrectangle,
Lpolygon,Polygon,Square,Lsquare,
Lstar,Star,TextArea,Ltextarea,
Ltextfield,TextField,TextBox,Ltextbox,
Ltriangle,Triangle,_,_,20,20),
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Constraints (Cont.)

• Tree constraints

Tnode(C0,node(C1,node(C3,
node(C4,)), node(C2,node(C5,),
node(C6,))), cgTree(T,top_down,10,10,centered)
.
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Event Handling

• Action rule
• Examples

Agent ConditionSeq Event gt ActionSeq
handleButtonClick(B),actionPerformed(B) gt
handleMousePress(O),mousePressed(O,E)
gt Ex X, Ey Y, write(mouse_pressed
_at(X,Y)),nl. handleKeyType(O),keyTyped(O,E)
gt Echar Char, write(Char).
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Other Primitives in CGLIB

• Packing and showing objects
• cgPack(O) cgShow(O)
• Altering and moving objects
• Oattr Value
• cgScale(O,F) cgResize(O,W,H)
• cgMove(O,X,Y)
• Animation
• cgSleep(Time)
• Generating Java applets
• cgStartRecord(FileName) cgStopRecord

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Demo of B-Prolog

• B-Prolog (Version 6.0)(www.probp.com)
• Graphical user interfaces
• Animation
• Information visualization
• Constraint satisfaction problems
• Games

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Related Work

• Programming Constraint Propagators
• Indexicals (GNU-Prolog Sicstus)
• Delay constructs
• Attribute variables (Eclipse)
• Constraint handling rules
• Graphics programming
• Postscript Latex
• Every detail must be specified
• Java Tcl/Tk
• Layout managers are helpful for certain layouts
• Constraints Constraint programming
• Sketchpad, ThinkLab, Amulet, SubArctic