Stefano Levialdi

Visual Query Systems for Databases

Visual query systems (VQSs) are query systems for databases that use visual representations to depict the domain of interest and express related requests. VQSs can be seen as an evolution of query languages adopted into database management systems; they are designed to improve the effectiveness of the human?computer communication. Thus, their most important features are those that determine the nature of the human?computer dialogue. In order to survey and compare existing VQSs used for querying traditional databases, we first introduce a classification based on such features, namely the adopted visual representations and the interaction strategies. We then identify several user types and match the VQS classes against them, in order to understand which kind of system may be suitable for each kind of user. We also report usability experiments which support our claims. Finally, some of the most important open problems in the VQS area are described.

An approach to usability evaluation of e-learning applications

Despite recent advances of electronic technologies in e-learning, a consolidated evaluation methodology for e-learning applications is not available. The evaluation of educational software must consider its usability and more in general its accessibility, as well as its didactic effectiveness. This work is a first step towards the definition of a methodology for evaluating e-learning applications. Specific usability attributes capturing the peculiar features of these applications are identified. A preliminary user study involving a group of e-students, observed during their interaction with an e-learning application in a real situation, is reported. Then, the proposal is put forward to adapt to the e-learning domain a methodology for systematic usability evaluation, called SUE. Specifically, evaluation patterns are proposed that are able to drive the evaluators in the analysis of an e-learning application.

Evaluating web sites: exploiting user's expectations

A new goal-based approach to measure usability of web sites is presented, strongly taking into account the customers expectations, which are often hardly foreseeable as a whole. After a general discussion on web site design issues, we present a short survey of evaluation methods currently used for web sites. We next introduce a new taxonomy of site categories in a three-dimensional space, derived from Aristotles rhetorical triangle, including different aspects of the site designers goals. In our approach, we use this taxonomy to identify a number of sites belonging to the same category, in order to carry out a comparative analysis of their features. This analysis is the basis for a two-shot generation of a form for the evaluation of that category of sites. In the first shot, the users fill a generic evaluation form, acquainting them with sites characteristics. They are next asked to perform specific tasks of their choice, according to what they expect from a site of the given category. They note their impressions and list those features they found useful; the analysis of their comments is exploited to formulate statements specific to the given category, to be added to the initial form (second shot). We found that the responses to the second, expanded form, provide more comprehensive criteria for site evaluation, and turn helpful to precisely locate flaws in site functionalities. After testing, our methodology has proved very promising and may be applied for the evaluation of any other site category, most of all those providing a set of special services.

Color-based image retrieval using spatial-chromatic histograms

Abstract The paper describes a new indexing methodology for image databases integrating color and spatial information for content-based image retrieval. This methodology, called Spatial-Chromatic Histogram (SCH), synthesizing in few values information about the location of pixels having the same color and their arrangement within the image, can be more satisfactory than standard techniques when the user would like to retrieve from the database the images that actually resemble the query image selected in their color distribution characteristics. Experimental trials on a database of about 3000 images are reported and compared with more standard techniques, like Color Coherence Vectors, on the basis of human perceptual judgments.

Pyramidal systems for computer vision

This book presents papers on image processing using supercomputers and array processors. Topics considered include parallel processing, computer architecture, performance, data-flow processing, algorithms, computer vision, pattern recognition, equipment interfaces, programming languages, silicon implementation on multiprocessor pyramid architecture, and fault-tolerance techniques in arrays for image processing.

MADCOW: a multimedia digital annotation system

Digital annotation of multimedia documents adds information to a document (e.g. a web page) or parts of it (a multimedia object such as an image or a video stream contained in the document). Digital annotations can be kept private or shared among different users over the internet, allowing discussions and cooperative work. We study the possibility of annotating multimedia documents with objects which are in turn of multimedial nature. Annotations can refer to whole documents or single portions thereof, as usual, but also to multi-objects, i.e. groups of objects contained in a single document. We designed and developed a new digital annotation system organized in a client-server architecture, where the client is a plug-in for a standard web browser and the servers are repositories of annotations to which different clients can login. Annotations can be retrieved and filtered, and one can choose different annotation servers for a document. We present a platform-independent design for such a system, and illustrate a specific implementation for Microsoft Internet Explorer on the client side and on JSP/MySQL for the server side.

PAPIA: Pyramidal architecture for parallel image analysis

In 1981 a national research program for the design, simulation and construction of a multiprocessor image processing system was started. After a first phase devoted to the comparison of suggested and existing systems and to the definition of a set of benchmarks and to the evaluation of the performances of the major classes of machines, a new system has been defined. The structure of the new system is based on a pyramid of processors and many applications in which this machine may be exploited are highlighted. The multiprocessor architecture has been fully designed and the chip will be built by an Italian silicon. foundry, the SGS company, within the framework of the multichip national project.

Tuning range image segmentation by genetic algorithm

Several range image segmentation algorithms have been proposed, each one to be tuned by a number of parameters in order to provide accurate results on a given class of images. Segmentation parameters are generally affected by the type of surfaces (e.g., planar versus curved) and the nature of the acquisition system (e.g., laser range finders or structured light scanners). It is impossible to answer the question, which is the best set of parameters given a range image within a class and a range segmentation algorithm? Systems proposing such a parameter optimization are often based either on careful selection or on solution space-partitioning methods. Their main drawback is that they have to limit their search to a subset of the solution space to provide an answer in acceptable time. In order to provide a different automated method to search a larger solution space, and possibly to answer more effectively the above question, we propose a tuning system based on genetic algorithms. A complete set of tests was performed over a range of different images and with different segmentation algorithms. Our system provided a particularly high degree of effectiveness in terms of segmentation quality and search time.

Defining visual languages for interactive computing

A novel definition of visual languages allows a uniform approach to satisfying the needs of visual reasoning faced in visual human-computer interaction. The way the machine associates a computational meaning with an image, and conversely, the way it generates an image on the screen from a computation are formally described. A definition of a visual sentence and of a visual language as a set of visual sentences is discussed. A hierarchy of visual languages is derived in relation to the requirements for intelligible, manageable and trustable interaction between humans and computers.

Visual strategies for querying databases

A number of interfaces, based on different techniques which better exploit the human senses, have been recently suggested and implemented so enlarging the bandwidth of the man-machine communication channel. The availability of graphical devices at low cost has given rise to a large diffusion of visual interfaces. The database field is particularly suited for such interfaces mainly because the database is often queried by a casual user, who may not be conversant with conventional query languages. The use of a visual tool may therefore help to access the database, without the dependency on the native language and the limitations imposed by the specific application area. The authors concentrate on the querying strategies developed in existing visual query systems (VQS) by defining a suitable taxonomy and analyzing how these systems can be compared against such a taxonomy.<<ETX>>