2,006 research outputs found
Current account patterns and national real estate markets
This paper studies the association between current account and real estate valuation across countries. We find a robust and strong positive association between current account deficits and the appreciation of the real estate prices/(GDP deflator). Controlling for lagged GDP/capita growth, inflation, financial depth, institution, urban population growth and the real interest rate; a one standard deviation increase of the lagged current account deficits is associated with an appreciation of the real estate prices by 10%. This real appreciation is magnified by financial depth, and mitigated by the quality of institutions. Intriguingly, the economic importance of current account variations in accounting for the real estate valuation exceeds that of the other variables, including the real interest rate and inflation. Among the OECD countries, we find evidence of a decline over time in the cross country variation of the real estate/(GDP deflator), consistent with the growing globalization of national real estate markets. Weaker patterns apply to the non-OECD countries in the aftermath of the East Asian crisis
Morphological and volumetrical feature-based designer's intents
Features are claimed to be the carriers of Designer's Intents (DI's) which are seldom defined, identified
and represented in Design-by-Features (DbF) systems. This paper presents an interpretation of
Designer's Intents for the Feature-based Modelling (FBM) context and emphasis will be given to the
Morphological Functional and Volumetrical Geometrical DI’s which express the basic behaviour of a
DbF system. DI's are also an important part of a validation system capable of reasoning about the
semantics of using features in a particular design. If features' characterisations via DI's are well
established and measurable the representation could be assessed as to its conformity with feature's
meaning and their semantics could be validated. It is considered that the better Designer's Intents are
understood and specified, the more useful Feature-based Modelling will become
Feature-based interaction: an identification and classification methodology
Features are an established means of adding non-geometric information and extra
geometric semantics to conventional computer aided design (CAD) systems. For some time it has
been realized that, although feature-based modelling is necessary for the next generation of
integrated design and manufacturing systems, the inherent feature interactions pose a difficulty in
representing and manipulating geometric designs. This paper presents a structured geometric spatial
feature interaction identification method based on a broad multilevel classification. Feature interaction
definitions and classifications have been surveyed and it is evident that, although many feature
interaction classifications have been proposed, there is a lack of a general framework. The
classification presented here encompasses existing feature interference cases found in the literature
and defines a singular framework that leads to a general classification structure. The framework is
presented and applied at three different levels and each interaction case is defined by feature
parameters rather than just geometric entities. The restrictions often found in other research
concerning contact:non-contact and concave:convex situations are avoided. The resulting classification
is easy to understand and implement because it uses simple rules based on commonly available
Boolean operators. Finally, an example component is presented and the advantages, uses and
applications of the classification scheme are discussed
Structured multi-level feature interaction identification
Features are an established means of adding non-geometric information and extra geometric semantics to conventional
CAD systems. It has been already realised that although feature-based modelling is necessary for the next generation of
integrated design and manufacturing systems, inherent feature interactions pose a difficulty in representing and
manipulating geometric design. This paper presents a structured multi-level geometric feature interaction classification
scheme implemented within a Design-by Feature (DbF) system for representation validation analysis. Various feature
interaction definitions and classification methods are first surveyed. The elements and the tests used for the
identification process are presented. The classification encompasses existing feature interference cases found in the
literature, uses a clear structure for the classification and, is applied at three different levels
Operating invalid feature-based models
A valid feature-based representation is one where
instantiated features in a model agree with the features'
expected behaviours, available and defined as a library.
Invalid feature-based models happen when manipulations
on the model change the interrelationship among features
therefore changing the behaviour of an instantiated
feature.
Freedom of manipulation is an intrinsic advantage
of using a CAD system and it is taken for granted.
However, even the most basic manipulation, such as
"adding" a feature to a model, is capable of disrupting the
validity of a representation. Furthermore, invalid models
could compromise the usefulness of any following
analysis on it.
Thus, identifying means to operate on an invalid
model to make it valid, through "revalidation operations",
is a necessity in Feature-based CAD systems. It allows
conventional CAD systems (usually more preoccupied
with representing and producing feature-like shapes
within a geometrically constrained environment) to
interface more easily for example with CAPP systems
(usually more preoccupied with planning problems than
with the correctness of the representation).
The framework of a feature-based validation
system, called FRIEND (Feature-based Reasoning
system for Intent-driven Engineering Design), and a
discussion on representation validity analysis is presented
with emphasis on identifying and discussing "revalidation
operations”
An intent-driven paradigm for feature-based design
A very important advantage of a feature-based modelling (FBM) system is claimed to be its ability to
capture and carry designer’s intents (DI’s), although this last term is rarely clearly defined. Feature’s extra nongeometrical
semantics, that are closely related to such designer’s intents, are used by many applications but never
related back to designer’s intents. Therefore, adopting the approach of defining of designer’s intents helps define
the role of features in the geometric design and, indeed, allows future feature-based modelling systems to better
represent, store and reuse such information. Moreover, it allows a more formal approach for manipulating,
verifying and maintaining DI’s throughout the design process, which is an invaluable support for really intelligent
CAD systems. This paper presents Designer’s Intents in the feature-based modelling context and exposes a
methodology used to effectivelly capture and manage and verify this extra information
Intent-driven reasoning priorities in a feature-based validation system
Feature-based representation validation seeks to find means to verify feature-based
representations in order to guarantee that feature's expected behaviours are met and that applications
that use the representation can be sure of the correctness of the feature-related data.
To achieve this, a clear definition of features and their behaviour is needed but cannot be found
in the literature. Instead of proposing yet another feature definition, an attempt was made to define
some basic common-sense characteristics for (prismatic) features that could be tested, analysed and
manipulated. These characteristics are called Intents because features are said to be the carriers of
designer's intents. Feature-based Designer's Intents (DI's) proved to be essential to the validation
framework because they define the scope of the Feature-based Modelling (FBM) utilisation. Also,
some DI's establish clearly the geometric-dependent behaviour of features and were found to be
closely related to validation. A prototype system called FRIEND, an acronym to Feature-based
Reasoning system for Intent-driven ENgineering Design, was implemented to perform feature-based
representation validation.
This paper details Designer's Intents (DI's) in the context of deign-by-feature representation
validation, presents Morphological Functional and Volumetrical DI's, their semantics and their
priority organisation inside the validation mechanism, as it was implemented within FRIEND
Feature modelling: a validation methodology and its evaluation
Geometric modelling techniques for computer-aided design are provided with formal validation methods to ensure that a valid model is made available to applications such as interference checking. A natural and popular extension to geometric modelling is to group geometric entities into features that provide some extra meaning for one or more aspects of design or manufacture. These extra meanings are typically loosely formulated, in which case it is not possible to validate the feature-based model to ensure that it provides a correct representation for a downstream activity such as process planning. This paper presents a methodology used to validate the feature-based representation which is based on the capture of designer’s intents related to functional, relational and volumetric aspects of the component geometry. The feature-based validation method has itself been validated through its application to a series of test parts which have been either drawn from the literature or created to demonstrate particular aspects. It is shown that the prototype system that has been developed is indeed capable of meaningful feature-based model validation and additionally provides extensive information that is potentially useful to a range of engineering and manufacturing analysis activities
Feature-based designer's intents
Feature-based modelling is considered an improvement on existing CAD systems. Features
are considered to be a medium that carries designer’s intents, but neither features nor designer’s
intent have widely accepted definitions. Morphological functional designer’s intents, defined as
common-sense behaviours of the (form) feature’s concept, have been defined and presented
within a feature-based representation validation system [4].
The process of “feature elicitation”, frequently implied to identify and categorise features,
comprises “featurization” and “featurization validation” processes which help specify an
appropriate feature library to be used in a particular application. In the research reported here a
similar approach, called “intent elicitation”, has been performed to identify and categorise
meaningful and measurable designer’s intents from the integrated CAD/CAM and Computer
Aided Process Planning (CAPP) domains.
The resulting classification and taxonomy is presented in this paper. It can be observed that
the classification encompasses morphological feature-based designer’s intents (FbDI’s), because
of the feature’s concept, and is application dependent. The identified FbDI’s have been used in a
feature-based reasoning system which has led to an intent-driven approach for feature-based
modelling where designer’s intents are an explicit and central aspect
Representation validation in feature-based modelling: a framework for design correctness analysis and assurance
Feature-based Modelling allows extra meaning to be added to geometry, but lacks the
equivalent geometric formalism usually found in computer-aided design (CAD) and
Geometric Solid Modelling (GSM) systems. CAD systems have been evolving into
constraint-based design environments instead of intent-driven ones where the designer can
use whatever manipulation is available in the system without been afraid of messages like
"manipulation not permitted". These messages usually restrain the user in order to avoid
representation changes and faulty or "unknown" situations.
A Design-by-Feature system with a representation validation framework is presented that
supports "Design for X", intent-driven modelling, encompasses existing low-level geometric
verifications, adds high-level rules to analyse and enrich the design and incorporates
operations to assure its correctness. Also it alleviates the designer from specifying each and
every geometric detail/relationship (improving productivity)
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