Giovanni Maria Sacco

Timestamps in key distribution protocols

The distribution of keys in a computer network using single key or public key encryption is discussed. We consider the possibility that communication keys may be compromised, and show that key distribution protocols with timestamps prevent replays of compromised keys. The timestamps have the additional benefit of replacing a two-step handshake.

Dynamic taxonomies: a model for large information bases

A novel taxonomic model for structuring and accessing large heterogeneous information bases is presented. The model is designed to simplify both classification and access by computer-illiterate people. It defines simple and intuitive operations to access large information bases at the conceptual level and at different levels of abstraction, in a totally assisted way, through a simple, yet effective visual interface. The model can also be used to summarize result sets computed by other query methods, such as information retrieval, shape retrieval, etc., and to provide user maps for complex hypermedia networks. The experience gained by applying this model to commercial applications is reported.

Buffer management in relational database systems

The hot-set model, characterizing the buffer requirements of relational queries, is presented. This model allows the system to determine the optimal buffer space to be allocated to a query; it can also be used by the query optimizer to derive efficient execution plans accounting for the available buffer space, and by a query scheduler to prevent thrashing. The hot-set model is compared with the working-set model. A simulation study is presented.

Dynamic Taxonomies and Faceted Search

Current access paradigms for the Web, i.e., direct access via search engines or database queries and navigational access via static taxonomies, have recently been criticized because they are too rigid or simplistic to effectively cope with a large number of practical search applications. A third paradigm, dynamic taxonomies and faceted search, focuses on user-centered conceptual exploration, which is far more frequent in search tasks than retrieval using exact specification, and has rapidly become pervasive in modern Web data retrieval, especially in critical applications such as product selection for e-commerce. It is a heavily interdisciplinary area, where data modeling, human factors, logic, inference, and efficient implementations must be dealt with holistically. Sacco, Tzitzikas, and their contributors provide a coherent roadmap to dynamic taxonomies and faceted search. The individual chapters, written by experts in each relevant field and carefully integrated by the editors, detail aspects like modeling, schema design, system implementation, search performance, and user interaction. The basic concepts of each area are introduced, and advanced topics and recent research are highlighted. An additional chapter is completely devoted to current and emerging application areas, including e-commerce, multimedia, multidimensional file systems, and geographical information systems. The presentation targets advanced undergraduates, graduate students and researchers from different areas from computer science to library and information science as well as advanced practitioners. Given that research results are currently scattered among very different publications, this volume will allow researchers to get a coherent and comprehensive picture of the state of the art.

Fragmentation: a technique for efficient query processing

A “divide and conquer” strategy to compute natural joins by sequential scans on unordered relations is described. This strategy is shown to always he better than merging SCBIIS when both relations must he sorted before joining, and generally better in practical cases when only the largest relation mutt be sorted.

Research Results in Dynamic Taxonomy and Faceted Search Systems

Metadata access to complex information bases through multidimensional dynamic taxonomies (aka faceted search) is rapidly becoming a hot topic both in research and in industry, where e-commerce applications based on this access paradigm are becoming pervasive. The dynamic taxonomy model was the first model to fully exploit multidimensional classification schemes and to integrate query and exploration into a single visual framework. We review a number of research results in data modeling, implementation, user interaction and emerging application areas of dynamic taxonomies and faceted search, originating from the Department of Informatics, University of Torino.

Distributed query evaluation in local area networks

Heuristic strategies to solve multirelational queries in local area networks using broadcast routing are presented. In broadcast routing (used in broadcast and ring networks), data transmitted by one site are received by all the other network sites. This fact is exploited to derive new strategies to minimize a linear combination of query response and total time.

Analysis and validation of information access through mono, multidimensional and dynamic taxonomies

Access to complex information bases through multidimensional, dynamic taxonomies (also improperly known as faceted classification systems) is rapidly becoming pervasive in industry, especially in e-commerce. In this paper, the major shortcomings of conventional, monodimensional taxonomic approaches, such as the independence of different branches of the taxonomy and insufficient scalability, are discussed. The dynamic taxonomy approach, the first and most complete model for multidimensional taxonomic access to date, is reviewed and compared to conventional taxonomies. We analyze the reducing power of dynamic taxonomies and conventional taxonomies and report experimental results on real data, which confirm that monodimensional taxonomies are not useful for browsing/retrieval on large databases, whereas dynamic taxonomies can effectively manage very large databases and exhibit a very fast convergence.

Uniform access to multimedia information bases through dynamic taxonomies

The problem of browsing and retrieval in multimedia information bases has been traditionally addressed by two different approaches: the first one uses normal query methods (db or IR queries) on metadata or on a textual description of each item. The second one works on primitive multimedia features (such as color, texture, etc.) and usually tries to find items that are similar to a specific selected item. Neither of these approaches is satisfactory for what is claimed to be the usual end-user task: the exploration of an information base in order to find interesting items. This paper shows how dynamic taxonomies, a model proposed for the intelligent exploration of heterogeneous information bases, can be extended in order to provide guided browsing and retrieval for multimedia information bases and seamlessly integrate access through metadata with methods based on primitive multimedia features. It provides an example of interaction and discusses current research issues that address probabilistic membership and granularity of descriptions.

Guided interactive information access for e-citizens

Governments, especially local ones, are using the web to provide a number of services that are mainly informative and aim at improving the quality of life of citizens and at promoting the local community “abroad”. These services include among others, job placement services, tourist information (hotels, restaurants, etc.), yellow pages to promote local industries and activities, and are supplied in addition to institutional services such as law, regulations and opportunities information bases. We argue that traditional methods commonly used by administrations to implement these services do not really work, and propose a new access paradigm based on conceptual manipulation. This paradigm is applied to a job placement example.