A KNOWLEDGE-BASED REVERSE DESIGN SYSTEM

FOR DECLARATIVE SCENE MODELING

Vassilios Golfinopoulos

Laboratoire Méthodes et Structures Informatiques – MSI, Faculté des Sciences, Université de Limoges

83, rue d’Isle, 87060 Limoges cedex, France

Technological Education Institute of Athens, Department of Computer Science,

Ag.Spyridonos St., 122 10 Egaleo, Greece

Vassilios Stathopoulos, George Miaoulis

Technological Education Institute of Athens, Department of Computer Science,

Ag.Spyridonos St., 122 10 Egaleo, Greece

Dimitri Plemenos

Laboratoire Méthodes et Structures Informatiques – MSI, Faculté des Sciences, Université de Limoges

83, rue d’Isle, 87060 Limoges cedex, France

Keywords: Declarative Modeling, Knowledge-Based Systems, Reverse Design, Computer-Aided Design.

Abstract: Declarative modeling allows the designer to describe a scene without the need to define the geometric

properties. The MultiCAD architecture implements the declarative forward design, accepting a declarative

description and generating a set of geometric solutions that meet the description. The aim of the presented

work is to settle the reverse design process through the RS-MultiCAD component, a knowledge-based

system, in order to extend MultiCAD declarative conception cycle to an automated iterative process. The

RS-MultiCAD receives a selected geometric solution, which is semantically understood, permits the

designer to perform geometric and topological modifications on the scene, and results a declarative

description which embodies the designer modifications. That declarative description leads to more

promising solutions by reducing the initial solution space.

1 INTRODUCTION

Declarative modeling is an approach (Lucas, 1989)

that allows the designer to describe a desired scene

without the need to define the geometric properties

overcoming CAD applications drawbacks. A set of

solutions are generated that meet the initial

description. A special approach of the declarative

modeling is declarative modeling by hierarchical

decomposition (Plemenos, 1991), which gives the

user the ability to describe a scene by top-down

decomposition at different levels of abstraction. The

objective of this method is to remedy the

disadvantages of the traditional geometric modeling

by allowing the description of a scene by its

properties, which can be imprecise and incomplete.

More accurately the declarative modeling makes

possible to indicate the properties, which verify the

desirable scene in several levels of detail allowing

thus a top-down design.

MultiCAD architecture (Miaoulis, 1996),

(Miaoulis, 1998) is an intelligent multimedia CAD

system, liberated of geometrical inflexibility that

accepts a declarative description of a scene and

produces a set of solutions that meet the description

itself.

Our goal is to implement the declarative reverse

design by constructing a new declarative description

from an initially selected geometric solution which

has been modified by the designer in order the

design process to become iterative automatically

until the system produces the most desirable

Golﬁnopoulos V., Stathopoulos V., Miaoulis G. and Plemenos D. (2006).

A KNOWLEDGE-BASED REVERSE DESIGN SYSTEM FOR DECLARATIVE SCENE MODELING.

In Proceedings of the Eighth International Conference on Enterprise Information Systems - AIDSS, pages 82-90

DOI: 10.5220/0002497200820090

 SciTePress

solutions. The new component is placed within the

MultiCAD architecture. The introduction of the new

component was first discussed in (Golfinopoulos,

2005) and the current work presents the functionality

that underlies the RS-MultiCAD prototype

component.

1.1 Declarative Conception Cycle

The declarative scene modeling is based on the

declarative conception cycle, which consists of three

sequential functional phases (Plemenos, 1995). The

first is the scene description phase, where the

designer describes how he perceives the scene by

specifying properties of the scene or leaving them

ambiguous. The second is the generation phase,

where the generator inputs the declarative model and

produces a set of solutions that meet the description

of the desired scene. The third is the solution

understanding phase, where the scene solutions are

visualized through a geometric modeler.

1.2 MultiCAD Architecture

The design environment of MultiCAD features a

rich set of modules. These include alternative

modules for solution generation using CSP

(Plemenos, 1997) or genetic algorithms (Vassilas,

2002), (Makris, 2005) as well as modules

responsible for introducing architectural knowledge

(Ravani, 2003), representation of architectural styles

(Makris, 2003), collaborative design (Golfinopoulos,

2004), and intelligent user profile (Plemenos, 2002),

(Bardis, 2005).

MultiCAD incorporates an object-relational

database (Miaoulis, 2000), which consists of five

logical inter-connected databases. The scene

database is supporting information describing the

scene models. The multimedia database is

containing all types of documents related to the

project. The knowledge base is containing all the

necessary information about type of objects, their

properties along with their relations. The project

database is manipulating with data concerning

planning, financial and other special aspects of each

project and finally the concept database (Ravani,

2004) is storing concepts representations.

The scene database is configured following the

Scene Conceptual Modeling Framework (Miaoulis,

2000). The description contains objects defined by

their properties, simple or generic ones, as well as

group of simple objects with properties in common.

Besides, the description contains three types of

relations between objects: meronymic (“is part of”,

“is included in”), spatial organization (“adjacent

south”, “equal length”) and reflective (“higher that

large”, “wider than deep”) relations. Finally, the

description also contains properties which describe

objects.

1.3 Related Work

It is evident that the forward design in the

declarative modeling transforms a declarative

description into a set of geometric representations.

The reverse design process (Vergeest, 2005), (Wang,

2003) is a workflow of design where, in our case,

the declarative description is constructed by the

geometric model obtained from the system database

or external source.

In the declarative modeling framework, the

XMultiFormes project (Sellinger, 1998), is a

previous work that integrates the two modelers by

using a special interface system to ensure that there

is full and complete transfer of information between

the declarative and a traditional geometric modeler.

This system translates the geometric representation

to one that is more suited to interactive modeling. A

labeling sub-system is responsible for capturing non-

geometric information, which is implied in the

declarative description and the geometric-to-

declarative conversion process converts a geometric

instance to declarative description.

According to (Peng, 2001) one of the application

areas of a reverse engineering is the reverse design.

The reverse design either creates a new product from

an initial model or feeds a recovered result back to

an existing product model to compare and update.

In (Fisher, 2004) is presented the contribution of

knowledge in reverse engineering problems. The

problems considered are how to enforce known

relationships when data fitting, how to extract

features even in very noisy data, how to get better

shape parameter estimates and how to infer data

about unseen features. Even if the current work

focuses on the reconstruction, it shows that the

applicability of domain knowledge, in the general

framework of the knowledge-based approach, plays

a significant role in the reverse process.

2 EXTENDED MultiCAD DESIGN

METHODOLOGY

The declarative conception cycle of MultiCAD

architecture can be extended to an iterative process

by using a reconstruction phase (Golfinopoulos,

2005) where the scene is understood semantically

and refined by adding more detailed descriptions in

A KNOWLEDGE-BASED REVERSE DESIGN SYSTEM FOR DECLARATIVE SCENE MODELING

successive rounds of declarative design process. In

that case undesirable designs are cut from the set of

solutions, the size of solution set after each round of

generation can be reduced and after a few iterations

the designer gathers all promising solutions. The aim

of the reconstruction phase is to receive a geometric

model and provide a new declarative description

enhanced with geometric constraints to the scene

declarative phase. The proposed system is a

knowledge-based system that implements the

declarative reverse design. Under the reconstruction

phase, the designer changes the geometry of the

scene by modifying the topological relations and

geometric aspects of the objects. These changes are

checked semantically and the special representation

is updated.

The extended MultiCAD design methodology

starts with the description of the desired scene in

terms of objects, relations and properties through an

interface. A rule set and object set are built

representing the designer requirements of the scene.

Initially, the object set consists of all objects of

different level of abstraction, and the rule set

consists of all relations, properties that the designer

has declared during the declarative description

phase. Based on that rule set, a set of geometrical

solutions is produced by a solution generator. The

solutions are visualized through a 3D viewer and the

designer selects the most desirable solution, which

can be edited. The reconstruction phase is

implemented through the RS-MultiCAD component,

which receives the selected scene and converts into a

stratified representation. The rule set and the object

set can be edited by adding, deleting, and changing

the objects, relations and properties of the scene.

The designer can proclaim his requirements

declaratively and geometrically during the

reconstruction phase. A new declarative description

is constructed, which contains the changes and a

new MultiCAD cycle starts resulting to more

promising solutions. The iterative process aims to

produce scenes, which meet the requirements, after

refinement. Figure 1 presents the MultiCAD design

methodology and the modeling levels.

3 RS-MultiCAD ARCHITECTURE

The RS-MultiCAD knowledge-based component

incorporates architectural domain specific

knowledge for constructing buildings. The basic

system architecture is modular giving the possibility

to further extensions. The component is based on

five main modules.

The import/export module is responsible for the

communication with the databases supporting the

input and output of geometric solution, the output of

a new declarative description which comes from

designer modifications, and finally the import and

export of a geometrical model (eg. dxf file format).

The latter enhances the interoperability of the system

since the designer can either import a design from

another CAD system and produce alternative

solutions or export the solution to other CAD system

and continue the design process.

The extraction module applies all domain

specific relation and property types in order to

extract all valid relations and properties of the

objects from a selected solution. The extraction

module is domain independent and facilitates the

extension of knowledge and concept database since

it parses the available knowledge from the database.

Declarative

Modeling

Type of

Relations

Type of

Objects

Solution Generation

Stratified

Modeling

Import/

Export

Model

Rule

Set

Type of

Properties

Object

Set

Description Phase

Generation Phase

Reconstruction Phase

Solution Understanding Phase

Geometric Model

Visualization

Figure 1: MultiCAD design methodology and modeling levels.

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The control module incorporates all necessary

mechanisms for building, manipulating and updating

the stratified representation. The stratified

representation is dynamic and constructed from the

designer selected solution with a top-down approach

and mainly consists of declarative and geometric

information. Declarative information can be

summarized into object set and rule set. Geometric

information deals with the geometry of each object

that constitutes the scene. The control mechanism is

event-driven and is responsible for the stratified

representation to ensure the correct transition from

one state to another. It handles the designer scene

modifications examining their semantic correctness

and properly updates the stratified representation by

propagating the changes in a mixed way.

The explanation module provides valuable

information about the system reasoning in cases

where a scene modification violates the rule set.

Finally, the RS-MultiCAD component incorporates

a graphical user interface with a 3D editor in order

to visualize the solutions and graphically receive the

designer requests. Figure 2 illustrates the RS-

MultiCAD system architecture.

3.1 The Stratified Representation

The need of representing geometrical and

declarative information leads to an approach of

using a stratified representation (Sagerer, 1997). A

model in order to become another type of model is

gradually transformed into a sequence of different

levels of abstraction by a sequence of processing

steps.

The stratified representation is an intermediate

level model necessary for connecting the declarative

with the geometric model, and embodies the two

distinct interconnected layers of representation, the

declarative layer which represents the scene

description with the hierarchical decomposition, and

the geometric layer which encapsulates the

geometric aspects of the objects.

The geometric layer of the stratified

representation is based on the bounding box

dimensions of each object which express the object

pure geometric properties, along with any extra

geometric information that can determine the shape

of the object.

RS-MultiCAD inputs a geometric model

produced by the solution generator. That geometric

model contains the geometric information of all

objects and their type as well. The stratified

representation is a dynamic semantic net with nodes

and directed arrows. Every node corresponds to an

object. The arrow label indicates the relations of the

nodes. The labels “parent” and “children” connect

nodes with same level of abstraction and represent

the meronymic relations. The labels “next” and

“previous” connect nodes with the same level of

abstraction and detail. The label “has-geometry”

connects nodes of different layers and represents the

geometry of an object. Finally, the label “has-

topology” connects nodes of the same level of

abstraction indicating the topological relations

among concepts and represents the reflective and

spatial relations.

The construction of the stratified representation is

a top-down process where the hierarchical

decomposition is built based on the geometric

information coming from the geometric model. For

Import/

Export

module

Rule

Set

Object

Set

Designer

GUI/

3D Editor

Control

module

Explanation

module

Extraction

module

Geometric

Model

(dxf, .. etc)

Multimedia

Scene

Concept

Knowledge

RS-MultiCAD

Stratified Representation

Figure 2: RS-MultiCAD system architecture.

A KNOWLEDGE-BASED REVERSE DESIGN SYSTEM FOR DECLARATIVE SCENE MODELING

every object, a node is created on the geometric

layer of the stratified representation. As long as all

nodes have been created, the pure geometric

properties lead to the hierarchical decomposition by

creating interconnected nodes on the declarative

layer of the representation. In Figure 3 appears a

typical stratified representation.

3.2 Scene Manipulation

The dynamic stratified model of RS-MultiCAD

allows the designer to perform geometric and

topological modifications on the scene. As soon as

the designer modifies the scene a special process

starts. Every designer modification must be checked

according to the rule set for its validity and if so the

stratified representation must be properly updated in

order to reflect the real state of the scene. RS-

MultiCAD provides two inference options according

to designer modification which may or may not be

activated. The first refers to check the modification

according to the rule set. A modification is valid as

long as no relation or property of the rule set is

violated otherwise the modification is invalid and is

canceled. If the designer decides not to check the

modifications according to the rule set, the control

module performs a set of mandatory conditions

ensuring the validity of the scene such as, non

overlapping objects of the same level of abstraction,

no object exceeding the overall scene limits, etc. The

second refers to add pure geometric properties to the

rule set that are inferred from the modifications. If

the designer moves an object to a new position, pure

geometric properties relative to move are adding in

the rule set.

The control module properly propagates the

modification by updating the geometric layer of the

representation and activating the extraction module

in order to recalculate all valid relations and

properties. If all relations, properties of the rule set

are not violated the changes are accepted and the

new state of the stratified representation is valid.

Otherwise, the explanation module is activated in

order to record all violated relations, properties of

the rule set and the control mechanism rolls the

representation back to the previous state.

Figure 4 illustrates the propagation policy that

control module follows. On the left-hand side, if a

modification occurs on a leaf node (marked node)

then the propagation starts from its brothers and

continues to ancestors (shaded area). On the right-

hand side, if a modification occurs on an abstract

node (marked node) then the propagation starts from

its children and brothers and continues to ancestors

(shaded area).

The modifications that can occur on the stratified

model refer to abstract or leaf node and can be

divided into two categories according to the

geometrical information that may be supplied by the

designer. In particular, the declarative modifications

are:

Geometric Layer

Geometric

properties

has-geometry

Geometric

properties

has-geometry

Geometric

properties

has-geometry

Geometric

properties

has-geometry

Geometric

properties

has-geometry

Geometric

properties

has-geometry

Geometric

properties

has-geometry

Geometric

properties

has-geometry

Declarative Layer

site

building garage

roof flat

kitchen bedroom bathroom

children/parent parent

children/parent

parent

parent parent

previous previous

wtl

ltw

ao, el, ew

aw,el,ew

ae,el,ew

lt lt

it=low

iw=low

Figure 3: The Stratified Representation.

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• The insertion of an abstract node in the stratified

model can be done by specifying firstly an

already existing node of the model as its parent

and secondly the nodes that become children of

the new abstract node. The result of such a

change will affect the stratified representation

since the object set changes.

• The deletion of an abstract node will eliminate

the sub-tree where the abstract node is root. The

result of such a change will affect the object set

and may affect the rule set as well. The

stratified representation must be updated in

order to reflect the current state of the scene.

• The designer changes the rule set by adding or

deleting a relation or a property of a node.

Moreover, the geometric modifications are:

• Move an object. The designer by providing the

new position moves the object. The stratified

representation must be updated since the move

may affect the position of other objects.

• Scale an object. The designer specifies the scale

factor of the object.

• Resize object. The designer resizes the object by

providing new values for the dimensions of the

object bounding box.

• Insert object. The insertion of a leaf node is

carried out by specifying the geometric

characteristics of the object.

Alter the extra geometric characteristics of an

object. In case where the shape of the object is

complex, the designer can alter the extra geometric

characteristics that define the shape of the object.

3.3 The Resultant Declarative

Description

As soon as the designer has completed all

modifications on the scene, RS-MultiCAD results in

a new declarative description which includes all

modifications required by MultiCAD in order to

generate in the next iteration more promising

solutions by reducing the initial solution space. RS-

MultiCAD provides two optional ways, the manual

and automated. In particular, RS-MultiCAD in the

manual way results in a new rule set that is based on

the initial rule set along with the new relations and

properties that have been changed by the designer.

In this way, RS-MultiCAD offers the designer the

possibility to drive the system to generate a solution

space that is nearer to his requirements.

Figure 5: The propagation policy.

Furthermore, the automated way is based on the

generalization factor (GF). Every hierarchical

GF=1

GF=2

GF=3

GF=4

Figure 4: The propagation policy.

A KNOWLEDGE-BASED REVERSE DESIGN SYSTEM FOR DECLARATIVE SCENE MODELING

decomposed tree is divided in distinct levels of

detail. The generalization factor is related to levels

of detail, and its values vary from 1 to maximum

tree depth. The rule set that results from the

automated option, is based on the initial rule set

along with all modifications and also all pure

geometric properties that are implied from the

generalization factor.

Figure 5 schematically shows which pure

geometric properties are included in the rule set

according to generalization factor. If the

generalization factor equals to 1, the pure geometric

properties of the root node are included in the rule

set. If the generalization factor equals to 3, the nodes

that provide their pure geometric properties to the

rule set, are the nodes of the three higher levels of

detail.

4 RS-MultiCAD

IMPLEMENTATION

RS-MultiCAD has been implemented on Microsoft

Visual Studio .NET platform using C# programming

language and incorporates VectorDraw Viewer

component. The working space of the prototype

presents, on the left-hand side the declarative layer

of the stratified representation, on the right-hand

side the geometric layer and in the middle the

visualized solution. The relations and properties that

belong to the rule set are marked. The current

example shows a site with a building and a garage

inside. The building is further decomposed into a flat

and a roof. The flat consists of a kitchen, bedroom

and bathroom. The stratified representation of the

example is presented in Figure 3.

Tables 1, 2, and 3 present the spatial relations,

reflective relations, and properties that initially

constitute the rule set of the example.

Table 1: Spatial relations.

Garage lower_than Building

Roof adjacent_over, equal_length,

equal_width

Flat

Kitchen adjacent_west, equal_length,

equal_width

Bedroom

Bathroom adjacent_east, equal_length,

equal_width

Bedroom

Bedroom longer_than Kitchen

Bedroom longer_than Bathroom

Table 2: Reflective relations.

Building longer_than_wide

Garage wider_than_long

Table 3: Properties.

Garage is_tall Low

Flat is_tall Low

Bathroom is_wide Low

In case the designer moves the object “flat” to a

new position that causes a possible move of the

children of the “flat”, since it is an abstract node.

The modification is propagating to ancestors

yielding the object “building” with its new position

and also to object “roof” since there is a relation

“adjacent over” in the rule set. Figure 6 illustrates

the result of this move operation.

In case the designer resizes the object “garage”

to a new length and width value, the system

propagates the change to object “building” without

affecting it because there is no relation in the rule set

that connects the two objects. Figure 7 illustrates the

result of the resize operation.

Figure 6: The result of the move operation.

Figure 7: The result of the resize operation.

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In case the designer inserts a new object, he has

to specify its type and position along with its parent.

The insertion of the new object “roof” causes

modifications on the stratified representation at both

the declarative and the geometric layers. Figure 8

illustrates the result of the insertion. In case the new

object is deleted, figure 7 represents the resulting

state of the scene.

In case the designer modifies the extra geometric

characteristics of the object “roof”, it causes changes

inside the bounding box of the object. The roof

modeling is based on (Makris, 2005). Figure 9

illustrates the changes.

Table 4 shows some experimental results

concerning the manual reduction of the solution

space in the next MultiCAD iteration after the

production of the new declarative description of RS-

MultiCAD. By adding a new relation to the initial

set, the solution space is reduced to solutions that

also satisfy the new designer requirements. Figure

10 shows some experimental results, in logarithmic

scale, concerning the automated production of the

new declarative description.

Table 4: Manual reduction of the solution space.

Rule Set N

Solutions

Initial set 32124

initial set + “building

adjacent_west garage”

9270

In each MultiCAD iteration cycle, RS-MultiCAD

constructs a declarative description by adding the

pure geometric properties of the lower level of

detail. MultiCAD in each round generates fewer

solutions and when the generalization factor is set to

maximum depth of the tree, generates one solution

indeed.

Figure 10: Automated reduction of the solution space.

5 CONCLUSIONS

The RS-MultiCAD is a new component of the

MultiCAD architecture, which receives a geometric

model and results into a declarative description. The

MultiCAD declarative conceptual cycle extends to

operate iteratively by the introduction of the

reconstruction phase. During this phase, the internal

representation of RS-MultiCAD, i.e. the dynamic

stratified representation, allows the designer to

manually affect the resultant declarative description.

This is achieved by modifying the scene topology

and the object geometry, in order for MultiCAD, in

the next iteration, to generate geometric solutions

that are closer to designer requirements.

Furthermore, RS-MultiCAD employs two alternative

options, the manual and the automated, which

conduce to the reduction of the solution space by

adding the appropriate pure geometric properties of

the objects to the resultant declarative description

thus also reducing the solution generation time.

RS-MultiCAD can be compared with

XMultiFormes (Sellinger, 1998). The XMultiFormes

project approaches the subject by a low-level

process and gives special attention on man machine

interaction. On the other hand, RS-MultiCAD uses a

high-level knowledge-based approach and supports

Figure 8: The result of insertion.

Figure 9: The result of changing extra geometric

characteristics.

32124

6120

760

100

1000

10000

100000

No Solutions

1234

Generalization Factor

A KNOWLEDGE-BASED REVERSE DESIGN SYSTEM FOR DECLARATIVE SCENE MODELING

the iterative process of the declarative modeling by

an automatic way. The reduction of the solution

space proves the quality of the resultant declarative

model in every cycle of the iterative process.

ACKNOWLEDGMENTS

This study was co-funded by 75% from the

European Union and 25% from the Greek

Government under the framework of the Education

and Initial Vocational Training Program –

‘Archimedes’.

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