1
Building Metaphors for Supporting
User Interaction with Multimedia
Databases
M. F. Costabile, D. Malerba
Dipartimento di Informatica, Università degli Studi di Bari
Via Orabona 4, I-70126 Bari, Italy
{costabile, malerba}@di.uniba.it
M. Hemmje, A. Paradiso
Integration Information Systems Institute, GMD
Dolivostrasse 4, D-64293 Darmstadt, Germany
{hemmje, paradiso}@darmstadt.gmd.de
Abstract
In this paper we discuss how metaphors for supporting user interaction with
multimedia databases can be automatically generated. The work presented is a
further step in the development of Virgilio, a Virtual Reality (VR) based system
that has been designed to be a general purpose exploration tool for highly
structured data. Virgilio visualizes the results of a query to a database by
generating VR scenes, that exploit appropriate metaphors in order to take
advantage of common knowledge about real world objects, thus reducing the
cognitive load in the process of information assimilation. We analyze two specific
components of the Virgilio architecture, the Query Management Tool and the
Metaphor Definition Tool, and we identify a completely automatic procedure to
define the metaphor that will be exploited in the construction of the VR scene. The
implementation of this procedure exploits the backtracking search strategy of
Prolog interpreters to solve a typical constraint satisfaction problem.
Keywords
Multimedia Database, User Interaction , Metaphor, Constraint Satisfaction
1 INTRODUCTION
In many of nowadays web-based environments for electronic marketing and
commerce, that present large multimedia product and service catalogues, it
becomes more and more difficult to provide naive end users, such as private
consumers or commercial business partners, with intuitive user interfaces to access
the large multimedia collections describing the presented products and services.
The same holds for marketing managers and other employees responsible for
managing and maintaining the large and constantly changing set of multimedia
information chunks and fragments contained in these collections.
As a consequence, many efforts are devoted to improve the quality of the
interaction between users and databases. Virtual Reality (VR) techniques are a
promising interaction paradigm particularly suited to novice and/or occasional
users. The users are facilitated in the database navigation since the system proposes
them an environment that reproduces a real situation and gives the possibility of
interacting by manipulating objects that have a direct correspondence with known
objects.
VR techniques combine the advantages of 3D visualizations with the power of
metaphorical representations. Presenting the result of a database query through a
VR scene allows users to explore data more easily since they interact with familiar
objects. The structural and dynamic properties of the objects in the virtual world,
i.e. the way objects can be composed and can act themselves, are predictable since
they belong to the users' general background. No particular training should be
required to interact with and explore the dataset, thus reducing the learning
overhead of naive users when accessing information.
Virgilio is a VR based system that has been designed to be a general purpose
exploration tool for highly structured data. It is capable of visualizing large sets of
objects of considerable intra-object and inter-object complexity through effective
VR techniques. Virgilio is based on several metaphors in order to take advantage
of common knowledge about real world objects, thus reducing the cognitive load
in the process of information assimilation. The overall system has been presented
in (Massari et al., 1997), where lot of emphasis was posed on the generation of the
3D scenes, once the metaphor exploited in the visualization was chosen in a semi-
automatic way, i.e. with the intervention of the system administrator. In this paper
we discuss how metaphors for supporting user interaction with multimedia
databases can be automatically generated in Virgilio. Therefore, we are more
concerned with specific components of the Virgilio architecture, the Query
Management Tool and the Metaphor Definition Tool, whose aim is to identify with
a completely automatic procedure the most appropriate metaphor to be exploited in
the construction of the VR scene.
Our work represents a further step in the Virgilio project, since we have
automated the choice of a proper VR visualization of the results of the user's query.
In other words, the definition of the mapping (or metaphor) between the query
result and objects of a virtual world, that was a task of the System Administrator in
the previous release of Virgilio is now performed automatically by the system.
The content of the paper is the following. Section 2 introduces the concepts of
logical, physical, and VR information spaces. Section 3 discusses metaphor in user
interfaces and illustrates its use in the Virgilio system. The architecture of Virgilio
is presented in Section 4. Section 5 describes the process that generates from a
query to the database all information necessary to the construction of the VR
scene. Section 6 gives the conclusions.
2 INFORMATION SPACES: FROM LOGICAL TO VR
In order to allow users easy access to a database, the information stored in the
database needs to be visualized in an information space. This visualization can
either be carried out by the user in the user's mind, in which case it is essentially
the user's conceptualization of the database; or the visualization could be
accomplished by the system, in which case the visualization is generated on the
display screen. The latter is what it is actually defined information visualization,
i.e. "a process of transforming information into a visual form enabling the user to
observe information" (Gershon et al., 1997). The essence of this process is to
visually present information that is non inherently visual, such as text. Recent
research has proved that successful visualization can reduce the time to get
information, and to make sense out of it; it also enhance creative thinking.
Database objects, in general, are abstracted from real-life objects in the real
world. Therefore, we can distinguish the logical information space and the physical
information space (Chang and Costabile, 1997). In the logical space, the abstract
database objects are represented. In the physical space, the abstract database
objects are materialized and represented as physical objects that reflect real-life
objects, such as diagrams, icons and sketches. For example, each object is
materialized as an icon, and the physical information space consists of a collection
of icons. These icons can be arranged spatially, so that the spatial locations
approximately reflect the relations among database objects.
To create visualizations, the information in the logical space must be mapped
into a physical space that will represent relationships contained in the information
faithfully and efficiently. In this way, users will exploit their innate abilities to
understand spatial relationships, also shifting most cognitive processing load to the
perceptual system.
In the physical information space, the objects reflect real-world objects, but the
world is still an abstract world. One further step is to present information in a VR
information space. VR allows the users to be placed in a 3D environment they can
directly manipulate. What the users see on the screen will be the same as what can
be experienced in the real world. 3D features can be used to present the results in a
VR setting. For example, if the database refers to the books of a library, we can
represent a Virtual Library in which the physical locations of books are indicated
by blinking icons in a 3D presentation of the book stacks of the library. What the
user sees on the screen will be the same (after simplifications) as what can be
experienced in the real world.
It is worth noting that we are talking about "nonimmersive" VR (Robertson et
al., 1993), that is the user is placed in a 3D environment he/she can directly
manipulate without wearing head-mounted stereo displays or special gloves, but
acting only with mouse, keyboard, and monitor of a conventional workstation.
The real world, from which the database objects are abstracted, is the
environment that the database objects must relate to. The real world is often
abstracted in the information space. Only in the VR information space will the real
world be represented in a direct way. Indeed, finding a good spatial representation
of the information at hand is one of the most difficult tasks in visualization of
abstract information. The key problem in information visualization is to invent
visual metaphors for non physical data (Gershon et al., 1997). Next section
discusses the power of metaphorical representation and their use in database
interaction.
3 METAPHOR IN USER INTERFACES
The literal meaning of metaphor (from the Greek word 'metaphorein') is to transfer
or to carry across. One of the most important aspects of metaphor is that it gives
the possibility of going from familiar concepts to unknown ones. The definition of
metaphor given by Lakoff and Johnson (1980) says "metaphor is a rhetoric figure,
whose essence is understanding and experiencing one kind of thing in terms of
another". Thanks to the metaphor we can move from familiar concepts to unknown
ones, thus incorporating new knowledge in old. Often, for introducing a new
concept we present it in relation to a well known one, thus simplifying the learning
process. For example, the model of the atom is usually presented with reference to
the structure of the solar system.
Metaphors consist of two sets of component concepts, a target component and
a source component (Martin, 1990). The target consists of the concepts we are
actually referring to (also said the original idea). The source refers to the concepts
in terms of which the intended target concepts are being viewed (the borrowed
idea). Conventional metaphors are represented as sets of associations, or relations,
between source and target concepts. Source and target concepts usually belong to
different domains, and the familiarity with the source domain is exploited to
understand the target concepts. The metaphor specifies how the source concepts
correspond to the various target concepts. It establishes a mapping between target
and source domains.
Metaphor is acknowledged as a fundamental tool in creative interface design,
since it provides the user with a friendlier environment to work with (Mountford,
1990; Erikson, 1990). It is well known that an ideal metaphor does not exist, but it
is extremely important to choose the metaphor which is appropriate depending on
the particular situation. Some insights on metaphorical design are given in
(Marcus, 1994; Madsen, 1994). In database interfaces, metaphors have been
exploited for representing the intensional part of the database, that is the data
schema; in such cases, the metaphor mediates between the data model and the user
(Haber et al., 1994; Catarci et al., 1995). Most end users are actually concerned
with the extensional part of the database, therefore it is appropriate to offer them a
scenario where the information contained in the database is metaphorically
represented in a VR environment, i.e. in a virtual world, so that the user is no
longer aware of a presence of a structured database, but he/she is interacting as in
the real world.
Virgilio is a system that supports the definition of a metaphor as a mapping
between data in the result of a query to a database and objects in a virtual world.
Several metaphors are actually available in the system, so that different mappings
between a same data set, representing the target domain, and different virtual
worlds, each representing a source domain, can be generated in order to present to
users the most effective environment for their preferences and expectations. One of
the most used virtual worlds in Virgilio is a "building" with several floors, and an
entrance with an elevator to reach different floors. On each floor, there is a
corridor with several rooms, and in each room there are pieces of furniture, as it
happens in the real world. Different virtual worlds are available in Virgilio: one is
a book store, where there are several areas, each one with several shelves on which
books are shown; another is a ship, with the different elements that are typical in
real ships. Yet, other virtual worlds can be input into the system. The main
contribution of this paper is the automatic construction of the mappings between
the dataset and the available virtual worlds, as described in Section 5.
4 VIRGILIO ARCHITECTURE IN BRIEF
The architecture of the overall Virgilio system, as described in (Massari et al.,
1997), is shown in Figure 1. The main components are: a) three modules, called
Query Management Tool, Metaphor Definition Tool, Virtual World Object Editor;
b) a global repository of information that includes three meta databases containing
information necessary to generate the visualizations, namely the Query Repository,
the Metaphor Repository and the Virtual World (VW) Objects Repository; c) the
Scene Constructor Server. The other items displayed in Figure 1, that is a DBMS
with the database storing the data the users want to access to, a Web Browser, and
an unspecified web network connection are considered external to Virgilio. The
database is assumed to be a generic one with a structure composed of different
kinds of objects, many semantic relationships, and possibly containing multimedia
data.
