33 research outputs found
Object-oriented querying of existing relational databases
In this paper, we present algorithms which allow an object-oriented
querying of existing relational databases. Our goal is to provide an improved query
interface for relational systems with better query facilities than SQL. This
seems to be very important since, in real world applications, relational systems
are most commonly used and their dominance will remain in the near future. To
overcome the drawbacks of relational systems, especially the poor query facilities
of SQL, we propose a schema transformation and a query translation algorithm.
The schema transformation algorithm uses additional semantic information to enhance
the relational schema and transform it into a corresponding object-oriented
schema. If the additional semantic information can be deducted from an underlying
entity-relationship design schema, the schema transformation may be done
fully automatically. To query the created object-oriented schema, we use the
Structured Object Query Language (SOQL) which provides declarative query facilities
on objects. SOQL queries using the created object-oriented schema are
much shorter, easier to write and understand and more intuitive than corresponding
S Q L queries leading to an enhanced usability and an improved querying of
the database. The query translation algorithm automatically translates SOQL queries
into equivalent SQL queries for the original relational schema
A Tutorial on Visual Representations of Relational Queries
Query formulation is increasingly performed by systems that need to guess a
user's intent (e.g. via spoken word interfaces). But how can a user know that
the computational agent is returning answers to the "right" query? More
generally, given that relational queries can become pretty complicated, how can
we help users understand existing relational queries, whether human-generated
or automatically generated? Now seems the right moment to revisit a topic that
predates the birth of the relational model: developing visual metaphors that
help users understand relational queries.
This lecture-style tutorial surveys the key visual metaphors developed for
visual representations of relational expressions. We will survey the history
and state-of-the art of relationally-complete diagrammatic representations of
relational queries, discuss the key visual metaphors developed in over a
century of investigating diagrammatic languages, and organize the landscape by
mapping their used visual alphabets to the syntax and semantics of Relational
Algebra (RA) and Relational Calculus (RC).Comment: 4 page tutorial paper at VLDB 2023, tutorial web page with slides to
be posted in time:
https://northeastern-datalab.github.io/visual-query-representation-tutorial/.
arXiv admin note: text overlap with arXiv:2208.0161
Federating Queries to RDF repositories
Currently large amounts of RDF data are being published in the Web. These data is commonly accessed by means of SPARQL endpoints. However to query a set of SPARQL endpoints new mechanisms are needed due to neither the SPARQL protocol nor the language provide any norms or guidelines about how to proceed. In this paper we present an approach for federating queries to a set of SPARQL endpoints, using relational database distributed query processing techniques and part of the WS-DAI specification for web-service based access to relational and XML databases
Database architectures for modern hardware: report from Dagstuhl Seminar 18251
The requirements of emerging applications on the one hand and the trends in computing hardware and systems on the other hand demand a fundamental rethinking of current data management architectures. Based on the broad consensus that this rethinking requires expertise from different research disciplines, the goal of this seminar was to bring together researchers and practitioners from these areas representing both the software and hardware sides and to foster cross-cutting architectural discussions. The outcome of this seminar was not only an identification of promising hardware technologies and their exploitation in data management systems but also a set of use cases, studies, and experiments for new architectural concepts
Towards an Efficient Evaluation of General Queries
Database applications often require to
evaluate queries containing quantifiers or disjunctions,
e.g., for handling general integrity constraints. Existing
efficient methods for processing quantifiers depart from the
relational model as they rely on non-algebraic procedures.
Looking at quantified query evaluation from a new angle,
we propose an approach to process quantifiers that makes
use of relational algebra operators only. Our approach
performs in two phases. The first phase normalizes the
queries producing a canonical form. This form permits to
improve the translation into relational algebra performed
during the second phase. The improved translation relies
on a new operator - the complement-join - that generalizes
the set difference, on algebraic expressions of universal
quantifiers that avoid the expensive division operator in
many cases, and on a special processing of disjunctions by
means of constrained outer-joins. Our method achieves an
efficiency at least comparable with that of previous
proposals, better in most cases. Furthermore, it is considerably
simpler to implement as it completely relies on
relational data structures and operators