7,430 research outputs found
A Review of integrity constraint maintenance and view updating techniques
Two interrelated problems may arise when updating a database. On one
hand, when an update is applied to the database, integrity constraints
may become violated. In such case, the integrity constraint maintenance
approach tries to obtain additional updates to keep integrity
constraints satisfied. On the other hand, when updates of derived or
view facts are requested, a view updating mechanism must be applied to
translate the update request into correct updates of the underlying base
facts.
This survey reviews the research performed on integrity constraint
maintenance and view updating. It is proposed a general framework to
classify and to compare methods that tackle integrity constraint
maintenance and/or view updating. Then, we analyze some of these methods
in more detail to identify their actual contribution and the main
limitations they may present.Postprint (published version
Automatic Verification of Transactions on an Object-Oriented Database
In the context of the object-oriented data model, a compiletime approach is given that provides for a significant reduction of the amount of run-time transaction overhead due to integrity constraint checking. The higher-order logic Isabelle theorem prover is used to automatically prove which constraints might, or might not be violated by a given transaction in a manner analogous to the one used by Sheard and Stemple (1989) for the relational data model. A prototype transaction verification tool has been implemented, which automates the semantic mappings and generates proof goals for Isabelle. Test results are discussed to illustrate the effectiveness of our approach
Transparent Dynamic reconfiguration for CORBA
Distributed systems with high availability requirements have to support some form of dynamic reconfiguration. This means that they must provide the ability to be maintained or upgraded without being taken off-line. Building a distributed system that allows dynamic reconfiguration is very intrusive to the overall design of the system, and generally requires special skills from both the client and server side application developers. There is an opportunity to provide support for dynamic reconfiguration at the object middleware level of distributed systems, and create a dynamic reconfiguration transparency to application developers. We propose a Dynamic Reconfiguration Service for CORBA that allows the reconfiguration of a running system with maximum transparency for both client and server side developers. We describe the architecture, a prototype implementation, and some preliminary test result
Integrity Control in Relational Database Systems - An Overview
This paper gives an overview of research regarding integrity control or integrity constraint handling in relational database management systems. The topic of constraint handling is discussed from two points of view. First, constraint handling is discussed by identifying a number of important research issues, and by treating each issue in detail. Second, a number of projects is described that have resulted in the realization of database management systems supporting integrity constraints; the various projects are compared with respect to a number of system characteristics. Together, both approaches give a broad overview of the state of the art in the field at this moment
Static Analysis of Partial Referential Integrity for Better Quality SQL Data
Referential integrity ensures the consistency of data between database relations. The SQL standard proposes different semantics to deal with partial information under referential integrity. Simple semantics neglects tuples with nulls, and enjoys built-in support by commercial database systems. Partial semantics does check tuples with nulls, but does not enjoy built-in support. We investigate this mismatch between the SQL standard and real database systems. Indeed, insight is gained into the trade-off between cleaner data under partial semantics and the efficiency of checking simple semantics. The cost for referential integrity checking is evaluated for various dataset sizes, indexing structures and degrees of cleanliness. While the cost of partial semantics exceeds that of simple semantics, their performance trends follow similar patterns under growing database sizes. Applying multiple index structures and exploiting appropriate validation mechanisms increase the efficiency of checking partial semantics
A database management capability for Ada
The data requirements of mission critical defense systems have been increasing dramatically. Command and control, intelligence, logistics, and even weapons systems are being required to integrate, process, and share ever increasing volumes of information. To meet this need, systems are now being specified that incorporate data base management subsystems for handling storage and retrieval of information. It is expected that a large number of the next generation of mission critical systems will contain embedded data base management systems. Since the use of Ada has been mandated for most of these systems, it is important to address the issues of providing data base management capabilities that can be closely coupled with Ada. A comprehensive distributed data base management project has been investigated. The key deliverables of this project are three closely related prototype systems implemented in Ada. These three systems are discussed
Final report on the farmer's aid in plant disease diagnoses
This report is the final report on the FAD project. The FAD project was initiated in september 1985 to test the expert system shell Babylon by developing a prototype crop disease diagnosis system in it. A short overview of the history of the project and the main problems encountered is given in chapter 1. Chapter 2 describes the result of an attempt to integrate JSD with modelling techniques like generalisation and aggregation and chapter 3 concentrates on the method we used to elicit phytopathological knowledge from specialists. Chapter 4 gives the result of knowledge acquisition for the 10 wheat diseases most commonly occurring in the Netherlands. The user interface is described briefly in chapter 5 and chapter 6 gives an overview of the additions to the implementation we made to the version of FAD reported in our second report. Chapter 7, finally, summarises the conclusions of the project and gives recommendations for follow-up projects
Verifying and Enforcing Application Constraints in Antidote SQL
Geo-replicated storage systems are currently a fundamental piece in the development of large-scale
applications where users are distributed across the world. To meet the high requirements regarding la-
tency and availability of these applications, these database systems are forced to use weak consistency
mechanisms. However, under these consistency models, there is no guarantee that the invariants are
preserved, which can jeopardise the correctness of applications. The most obvious alternative to solve
this problem would be to use strong consistency, but this would place a large burden on the system.
Since neither of these options was feasible, many systems have been developed to preserve the
invariants of the applications without sacrificing low latency and high availability. These systems,
based on the analysis of operations, make it possible to increase the guarantees of weak consistency
by introducing consistency at the level of operations that are potentially dangerous to the invariant.
Antidote SQL is a database system that, by combining strong with weak consistency mechanisms,
attempts to guarantee the preservation of invariants at the data level. In this way, and after defining
the concurrency semantics for the application, any operation can be performed without coordination
and without the risk of violating the invariant. However, this approach has some limitations, namely
the fact that it is not trivial for developers to define appropriate concurrency semantics.
In this document, we propose a methodology for the verification and validation of defined prop-
erties, such as invariants, for applications using Antidote SQL. The proposed methodology uses a
high-level programming language with automatic verification features called VeriFx and provides
guidelines for programmers who wish to implement and verify their own systems and specifications
using this tool.Os sistemas de armazenamento geo-replicados são atualmente uma peça fundamental no desenvolvi-
mento de aplicações de grande escala em que os utilizadores se encontram espalhados pelo mundo.
Com o objetivo de satisfazer os elevados requisitos em relação à latência e à disponibilidade destas
aplicações, estes sistemas de bases de dados vêem-se obrigados a recorrer a mecanismos de consistên-
cia fracos. No entanto, sob estes modelos de consistência não existe qualquer tipo de garantia de que os
invariantes são preservados, o que pode colocar em causa a correção das aplicações. A alternativa mais
óbvia para resolver este problema passaria por utilizar consistência forte, no entanto esta incutiria
uma grande sobrecarga no sistema.
Sendo que nenhuma destas opções é viável, muitos sistemas foram desenvolvidos no sentido de
preservar os invariantes das aplicações, sem contudo, abdicar de baixas latências e alta disponibilidade.
Estes sistemas, baseados na análise das operações, permitem aumentar as garantias de consistência
fraca com a introdução de consistência ao nível das operações potencialmente perigosas para o invari-
ante.
O Antidote SQL é um sistema de base de dados que através da combinação de mecanismos de
consistência fortes com mecanismos de consistência fracos tenta garantir a preservação dos invariantes
ao nível dos dados. Desta forma, e depois de definidas as semânticas de concorrência para a aplicação,
qualquer operação pode ser executada sem coordenação e sem perigo de quebra do invariante. No
entanto esta abordagem apresenta algumas limitações nomeadamente o facto de não ser trivial para
os programadores definirem as semânticas de concorrência adequadas.
Neste documento propomos uma metodologia para a verificação e validação de propriedades defi-
nidas, como os invariantes, para aplicações que usam o Antidote SQL. A metodologia proposta utiliza
uma linguagem de programação de alto nível com capacidade de verificação automática designada
por VeriFx, e fornece as diretrizes a seguir para que o programador consiga implementar e verificar
os seus próprios sistemas e especificações, utilizando a ferramenta
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