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Formalisme noyau :
Graphes Conceptuels de Base
Ball:*
Cube:*
Ball:*
Color:*
Cube:A
between
carac carac
onTop
Labels are taken in the vocabulary (or support)
1
1
1 1
2
2
2 2
3
Basic conceptual graph (BG)
Two kinds of nodes :
• “concept nodes” represent entities
• “relation nodes” represent relationships
between these entities
The vocabulary (or support)
T
Animate
Colour
Inanimate
Object
Cube
Property
RegularObject
Ball
Bloc
between(...,...,...) near(...,...)
adjoin (...,...)
1. TC : Poset of concept types
2. TR : Poset of relation types partitioned into types of same arity
3. I : Set of individual markers
onTopOf (...,...)
V or S = (TC, TR, I)
* : the generic marker
[and : typing of individuals, relation signatures, …]
Ball:*
Cube:*
Ball:*
Color:*
Cube:A
between
carac carac
onTop
A
Labels are takenin the support
1
1
1 1
2
2
2 2
3
“There is a cube, which is on top of cube A, and there are balls, with same color, A being between these balls”
Basic conceptual graph (BG)G = (C, R, E, l)
Let’s compare BGs …
(t,m) (t’,m’) if and only if t t’ and m m’
where the order over I{*} is as follows:
for all i in I, * > i
for all i and j in I, i and j are non comparable
Ex: compute the partial order on the following labels:
(Cube, A) (Cube,*) (RegularObject,*)
(Ball,*) (RegularObject,B) (Ball,B)
First : how to compare labels ?
Poset of concept labels
« Projection » (BG Homomorphism)
« is the knowledge encoded in graph Q present in graph G ? »« does G provides an answer to Q? »
Mapping from the nodes of Q to the nodes of G, which:
• preserves bipartition
• preserves edges and their numberingif c-i-r then (c)-i-(r)
• may specialise labels type subtype generic marker individual marker
GQ?
Q: “Are there an object on top of a big cube and a gray object?”
Object
Cube
onTop
1
2
Object
Color:gray
carac
1
2
Size:big
carac
fact G
Ball
Color:gray
Cube
carac
onTop
1
1
2
2
onTop
Cube
carac
carac
Size:big
1
2
1
1
1
2
2
2
query Q
r1 r2
r3
r4 r5
r6
r7
r8
c1 c2
c3 c4
c5
d1 d2
d3
d4
d5
Object
Cube
onTop
1
2
Object
Color:gray
carac
1
2
Size:big
carac
query Q fact G
Ball
Color:gray
Cube
carac
onTop
1
1
2
2
onTop
Cube
carac
carac
Size:big
1
2
1
1
1
2
2
2
Image graph 1: there is a ball on top of a big gray cube
c1 c2
c3 c4
c5
d1 d2
d3
d4
d5
r1 r2
r3
r4 r5
r6
r7
r8
Object
Cube
onTop
1
2
Object
Color:gray
carac
1
2
Size:big
carac
query Q fact G
Ball
Color:gray
Cube
onTop
1
1
2
2
onTop
Cube
carac
carac
Size:big
1
2
1
1
1
2
2
2
carac
Image graph 2: there is a ball on top of a big cube and there is a gray cube
c1 c2
c3 c4
c5
d1 d2
d3
d4
d5
r1 r2
r3
r4 r5
r6
r7
r8
Project:P
Researcher Researcher:K Researcher:J
Office:#124
Office
member
in in
in
near
Query Q Fact G
member
Person Person
member
Project Project
Q: “Are there people working together, who are each member of a project?”
worksWith
worksWith
member member
Project:P
Researcher Researcher:K Researcher:J
Office:#124
Office
member member member
in in
inworksWith
near
Query Q Fact G
member
worksWith
Person Person
member
Project Project
Specialisation/Generalisation
Projection defines a generalisation relation among SGs
Q G (G Q)
if there is a homomorphism from Q to G
Q is more general than G
G is more specific than Q
Problème fondamental : BG-Homomorphisme
Données : deux BGs G et H Question : y-a-t-il un homomorphisme de G dans H?
(problème NP-complet)
Classical graph homomorphism is a particular case of BG homomorphism
• A graph homomorphism h from G=(VG, EG) to H=(VH,EH) is a mapping from VG to VH that preserves edges:
if (x,y) is in EG, then (h(x),h(y)) is in EH
a
b
c
d
3
1 2
G
H
From graph homomorphism to BG homomorphism
T
T
r
1
2
TC = {T}TR ={r}M = {*}
Support
There is a homomorphism from a graph G to a graph H if and only if there is a BG-homomorphism from f(G) to f(H)
f
From BGs to graphs ? There is a polynomial transformation too…
T Tp
T Tp
p T
T Tp
p T
Tp
p
Ex : Relationships between these BGs?
Specialization is reflexive, transitive but not antisymmetric: it is a preorder
Quelle sémantique pour les BGs ?
Intuitivement : un BG représente l’existence d’entités et de relations entre ces entités
“There is a cube, which is on top of cube A, and there are balls, with same color, A being between these balls”
Sémantique ensembliste (ou théorie des modèles)
Sémantique logique
Besoin d’une sémantique formelle
Ca n’est pas assez précis : Combien y-a-t-il d’objets ? Sont-ils tous différents ?Est-il sous-entendu que ces objets ont tous une couleur?Peut-il y avoir un autre objet sur le cube A? Si on a « onTop » ou « between » a-t-on aussi « near » ?
First-order logical semantics ()
Translation of the Support
types (concept/relation) predicatesindividual markers constants
‘subtype’ partial order formulas
concept types t < t’ x t(x) t’(x)
x Bloc(x) Object(x)
relation typesr < r’ x1... xk r(x1,..., xk) r’(x1,..., xk)
x1x2 adjoin(x1,x2) near(x1,x2)
(S) is the set of the formulas translating the type posets
Translation of a BG
Ball:*
Cube:*
Ball:*
Color:*
Cube:A
between
carac carac
onTop
x
A
y z
u
1
1
1 1
2
2
2 2
3
• For each generic concept node, a new variable
• For each individual concept node with marker i, the constant assigned to i
Cube(x)
Cube(A)
Ball(z)Ball(y)
Color(u)
onTop(x,A)
carac(y,u) carac(z,u)
Ball:*
Cube:*
Ball:*
Color:*
Cube:A
between
carac carac
onTop
x
A
y z
u
1
1
1 1
2
2
2 2
3
between(A,y,z)
Cube(x) Cube(A) Ball(y) Ball(z) Color(u) onTop(x,A) between(A,y,z) carac(y,u) carac(z,u)
xyzu
• For each node,an atom
Quelle sémantique pour l’homomorphisme?
• S’il existe un homomorphisme de Q dans G, cela veut dire quoi?
Intuitivement : « la connaissance représentée par Q est aussi présente dans G », « G est plus précis que Q », « on peut déduire Q de G », «G implique Q »
Formellement : (Q) se déduit de (G) et de (S)
• Et s’il n’existe pas d’homomorphisme de Q dans G, que peut-on en conclure?
« fondés par rapport à une logique »
Les raisonnements doivent être fondés par rapport à la déduction dans cette logique
• adéquats, corrects(sound) : si i peut être inféré de K alors f(i) est déductible de f(K)
• complets (complete) : si f(i) est déductible de f(K) alors i peut être inféré de K
K Ensemble de formulesdans une logique
f
Sémantique logique
A reformuler en termes de BGs
BGs are logically founded
Support S
t < t’r < r’
Graphs (BGs)
predicates, constantsx t(x) t’(x)x1... xk r(x1,..., xk) r’(x1,..., xk)
( , ) formulas
Soundness: if Q G then (Q) deducible from (G), (S)
Completeness: if (Q) deducible from (G), (S) then Q G• the BG model is equivalent to the ( , ) FOL fragment(without function)
(one can get rid off universally quantified formulas associated with the support)
• BG homomorphism is equivalent to deduction
Une limitation à la complétude
Le BG homomorphisme est complet par rapport à la déduction si le graphe cible est sous forme normale
T:a r T:b
s T:b
T:a r T:b
sT:a
(G) et (H) équivalentesmais G et H incomparables par homomorphisme
Un graphe est sous forme normale s'il n'a pas deux sommets concepts avec le même marqueur individuel
T:a r T: b
s
G H
The BG model
Support (vocabulary)
Basic (conceptual) graphs defined on support
Operations
BG Homomorphism (« Projection »)
Logical language
Formulas
Deduction
FOL