ΔΗΜΟΣΙΕΥΣΕΙΣΓιάννης Ιωαννίδης
1996
Many commercial database systems use some form of statistics, typically histograms, to summarize the contents of relations and permit efficient estimation of required quantities. While there has…
The problem of translating database objects into a flat format to be written out in a flat Ascii file or, conversely, translating the contents of a file into a complex database object arises in…
Scheduling query execution plans is an important component of query optimization in parallel database systems. The problem is particularly complex in a shared-nothing execution environment, where…
Among existing tools for laying out large collections of visual objects, some perform automatic layouts, possibly following some rules prespecified by the user, e.g., graph layout tools, while…
Many commercial database systems maintain histograms to summarize the contents of relations and permit efficient estimation of query result sizes and access plan costs. Although several types of…
Several modules of a database system require estimates of (sub)query result sizes, e.g., query optimizers or sophisticated user interfaces providing such estimates as feedback to users before a…
This short report summarizes the discussions and recommendations of the working group on “Query Optimizer Benchmarks and Cost Model Verification”. It does not propose an actual benchmark, but…
Physical data independence is touted as a central feature of modern database systems. It allows users to frame queries in terms of the logical structure of the data, letting a query processor…
Given a query, there are many access plans that a database management system (DBMS) can follow to process it and produce its answer. All plans are equivalent in terms of their final output but vary…
1995
This paper examines the scheduling of concurrent requests on multimedia storage servers consisting of multiple resources, which is a central issue in processing and optimization of complex queries…
Conjuctive queries are queries over a relational database and are at the core of relational query languages such as SQL. Testing for containment (and equivalence) of such queries arises as part of…
Several recent trends have changed the usage and users of schemas beyond those of a database administrator’s tool for describing database contents. Distribution of computing power to the desk-top…
Many current database systems use some form of histograms to approximate the frequency distribution of values in the attributes of relations and based on them estimate some query result sizes and…
Many current database systems use histograms to approximate the frequency distribution of values in the attributes of relations and based on them estimate query result sizes and access plan costs.…
1994
Several types of data organizations have been proposed in the literature for object-oriented and relational databases. In studying these organizations, there appears to be no underlying common…
Physical data independence is touted as a central feature of modern database systems. Both relational and object-oriented systems, however, force users to frame their queries in terms of a logical…
Many aspects of database systems have been improved by Graphical User Interfaces (GUIs). One area that has not received adequate attention in GUI research is the visual presentation of schemas,…
When we, humans, talk to each other we have no trouble disambiguating what another person means, although our statements are almost never meticulously specified down to very last detail. We “fill…
In the spirit of interdependence of the different areas of CHI research, we present a description of OPOSSUM, a visualization tool inspired by concepts from heterogeneous databases. OPOSSUM is a…
Current theoretical work offers measures of schema equivalence based on the information capacity of schemas. This work is based on the existence of abstract functions satisfying various…
We describe the design and implementation of BERMUDA, which is a loosely coupled system interfacing Prolog to the Britton-Lee Intelligent Database Machine (IDM-500). BERMUDA allows multiple…
Current theoretical work offers measures of schema equivalence based on the information capacity of schemas. This work is based on the existence of abstract functions satisfying various…
1993
Many current relational database systems use some form of histograms to approximate the frequency distribution of values in the attributes of relations and on this basis estimate query result sizes…
Several graph-based algorithms have been proposed in the literature to compute the transitive closure of a directed graph. We develop two new algorithms (Basic_TC and Global _DFTC) and compare the…
Many current relational database systems use some form of histograms to approximate the frequency distribution of values in the attributes of relations and based on them estimate query result sizes…
Fox (Finding Objects of eXperiments) is the declarative query language for Moose (Modeling Objects Of Scientific Experiments), an object-oriented data model at the core of a scientific experiment…
In this paper, we carefully explore the assumptions behind using information capacity equivalence as a measure of correctness for judging transformed schemas in schema integration and translation…
Before the problem of schema integration and translation can be adequately addressed, a precise understanding of schemas is needed. We present an analysis of the notion of schema as used by…
Traditionally, the scale and scope of an experimental study was determined by the ability of the research team to generate data. Over the past few years, we have been experiencing an unprecedented…
1992
When a set of rules generates (conflicting) values for a virtual attribute of some tuple, the system must resolve the inconsistency and decide on a unique value that is assigned to that attribute.…
In this paper, we identify some of the fundamental issues that must be addressed in designing a desktop Experiment Management System (EMS). We develop an abstraction of the set of activities…
We investigate the role of commutativity in query processing of linear recursion. We give a sufficient condition for two linear, function-free, and constant-free rules to commute. The condition…
This paper presents the results of an experimental evaluation of the performance of three main algorithms for transitive closure: Seminaive, Smart and Blocked Warren. The algorithms have been…
In most database systems, the values of many important run-time parameters of the system, the data, or the query are unknown at query optimization time. Parametric query optimization attempts to…
This paper examines the idea of incorporating machine Iearning algorithms into a database system for monitoring its stream of incoming queries and generating hierarchies with the most important…
If one were to conduct a survey among researchers from all sciences asking for the greatest challenges in their particular discipline, one would expect very different answers from scientists of…
We describe an effort to develop a prototype database system for scientific data generated from controlled experiments or direct observations and concentrate on the user interface module of the…
1991
Current query optimization techniques are inadequate to support some of the emerging database applications. In this paper, we outline a database query optimization problem and describe the…
We present a combination of analytical and experimental results that shed some light into the shape of the cost function of the strategy spaces that query optimizers must deal with. These are the…
Query optimizers of current relational database systems use several statistics maintained by the system on the contents of the database to decide on the most efficient access plan for a given query…
An algebraic framework for the study of recursion has been developed. For immediate linear recursion, a Horn clause is represented by a relational algebra operator. It is shown that the set of all…
1990
Query optimization for relational database systems is a combinatorial optimization problem, which makes exhaustive search unacceptable as the query size grows. Randomized algorithms, such as…
