Heterogeneous Distributed Database Systems Research Articles

Data Synchronization for Distributed Heterogeneous Database

Heterogeneous distributed database concurrent data is one of the important topics of heterogeneous databases that have important meaning. This paper discusses the mechanism of optimizing data synchronization for distributed heterogeneous database and trying to propose real solutions. Database synchronization is the exchange of records in databases on the condition that they are different. When modifications are made to a specific database, they will be applied to the database that has been synchronized in different environments and servers horizontally. The synchronization is either a one-way or two-way application and can be incidental, i.e. it is synchronous to the local network and asynchronous to the Internet due to its lagging technology. Heterogeneous distributed database systems consisting of a row storage database and a column storage database will face many difficulties, due to the inconsistent storage type such as: synchronization speed mismatch in data synchronization compared to a homogeneously distributed database system. Heterogeneous database management systems work on exchanging information for a package of various formats, accessing modification information in a heterogeneous database, maintaining the independence of the proposed system, and ensuring a good application of the proposed system in order to reach data synchronization between several packages of databases.

Reducing Execution Time of Distributed SELECT Query in Heterogeneous Distributed Database using Genetic Algorithm

Centralized unit that coordinates different types of schema running on multiple sites is getting importance now-a-days. Heterogeneous Distributed Database System (HDDS) is the collection of multiple different databases management systems running on multiple systems that are linked together. Query processing is complicated in such cases. In this work we concentrate on utilizing Genetic Algorithm for finding optimized query execution plan for distributed SELECT queries. Selecting the right set of plans for queries using Genetic Algorithm which minimizes the total execution time is the major goal of this work. Replication of schema is used in this work which gives multiple solutions for retrieval of the data. We used Chromosome for specifying plan for query. Chromosome structures consist of combination of data site and join order. Aglet, Mobile agent, is used to connect all the database servers with centralized server. By implementing this, we get the optimized plan for the select query.

Development of a Message-Oriented Middleware for a Heterogeneous Distributed Database Systems

Middlewares are enabling technologies for the development, deployment, execution and interaction of applications. These software layers are standing between the operating systems and applications. They have evolved from simple beginnings hiding network details from applications into sophisticated systems that handle much important functionality for distributed applications providing support for distribution, heterogeneity and mobility. This paper concerns with the development of a Message_Oreinted Middleware (MOM) for a distributed database system. Middleware is a distributed software layer, or ‘platform’ which

Integrating Different Semantics of Classification Levels in Heterogeneous Distributed Database System

Integrating Different Semantics of Classification Levels in Heterogeneous Distributed Database System

Global scheduling for flexible transactions in heterogeneous distributed database systems

A heterogeneous distributed database environment integrates a set of autonomous database systems to provide global database functions. A flexible transaction approach has been proposed for the heterogeneous distributed database environments. In such an environment, flexible transactions can increase the failure resilience of global transactions by allowing alternate (but in some sense equivalent) executions to be attempted when a local database system fails or some subtransactions of the global transaction abort. We study the impact of compensation, retry, and switching to alternative executions on global concurrency control for the execution of flexible transactions. We propose a new concurrency control criterion for the execution of flexible and local transactions, termed F-serializability, in the error-prone heterogeneous distributed database environments. We then present a scheduling protocol that ensures F-serializability on global schedules. We also demonstrate that this scheduler avoids unnecessary aborts and compensation.

Achieving high degree of concurrency in multidatabase transaction scheduling: MTOS

Abstract A multidatabase system (MDBS), which is also called a heterogeneous distributed database system (HDDBS) or federated database system (FDBS), is a facility that allows users or applications to access data located in multiple local database systems (LDBSs), each of which is autonomously operated. Several practical MDBS concurrency control schemes have been proposed whilst maintaining global consistency without compromising local autonomy. However, they could degrade either local concurrency of local transactions or global concurrency of global transactions for the purpose of ensuring the global serializability. In this paper, we propose a new ticket-based global concurrency control scheme that employs multiple tickets at each site. The basic idea is that, with proper consideration of the potential cyclic global serialization orders, subtransactions with the possibility of the local indirect conflicts must access the same ticket at their sites, otherwise they are allowed to access the different tickets. This scheme alleviates the blockage on local resources, and, as a result, increases both global concurrency and local concurrency, whilst preserving the local autonomy.

Group-oriented catalog allocation in heterogeneous distributed database systems

The catalog is a system database, which contains information regarding various objects that are of interest to the system itself. In heterogeneous distributed database systems (HDDBSs), efficient handling of the global catalog is of great practical importance with respect to the site autonomy, global query optimization, global view management, authorization mechanism, and data distribution transparency. In this paper, we propose a new catalog allocation scheme, named GOCAS ( group-oriented catalog allocation scheme). GOCAS can reduce the number of inter-site messages for accessing catalog information by exploiting the locality of references that span a number of sites. This approach is contrary to the previous catalog allocation schemes, where the iocality of references cannot be employed or can be applied restrictively to only one site. We develop an analytical model in order to compare the performance of GOCAS to other schemes. With the analytical model, we describe the performance benefits of GOCAS and its effectiveness to other schemes.

Query transformation in heterogeneous distributed database systems

A heterogeneous Distributed Database Management system is organized as a federation of nodes with different functional capabilities and using different nodal query languages. The problem of query decomposition and translation is investigated and two approaches are identified as direct translation and a translation using an intermediate canonical language. The use of universal symbolic manipulation techniques instead of dedicated cross-translators to perform query transformation is suggested.

Integrating heterogeneous distributed database system

This paper demonstrates various aspects of resolving possible data conflicts occurring in the database integration process. A general model of a Heterogeneous Distributed Database System (HDDBS) based on a relational data model is presented. We also discuss the problems of heterogeneous database integration and the principal user requirements, together with design and implementation issues. The HDDBS suppresses differences of DBMS, language, and data models among the databases and provides users with a unified global schema and a single high-level query language. There are three principal research goals of the paper. The first goal is to develop appropriate language constructs for accessing and integrating heterogeneous databases. The Second goal is to discover effective global and local optimization techniques. The final goal is to design methods for handling incompatible data representations and inconsistent data.

A heterogeneous distributed database system for distance education networks

Abstract The exponential increase in the amount of information available makes the development of efficient information access systems essential. A heterogeneous distributed database system (HDDS) is an interconnected collection of logically related databases. Recent advances in database design, particularly the introduction of HDDSs, can offer distance education networks viable, simple, cost‐effective and efficient database access systems. Telecommunications users are becoming more and more sophisticated, demanding interoperability in a flexible, user‐friendly environment. The World Wide Web, Gopher, WAIS, and other Internet navigation tools are making access less difficult. Although implementing a heterogeneous distributed database system may add complexity, it would be consistent with present developments while providing a more efficient service to the students, teachers, researchers, and administrators who are using distance education networks. Implementing a HDDS can be an efficient way to manage the...

Divergence control for distributed database systems

This paper presents distributed divergence control algorithms for epsilon serializability for both homogeneous and heterogeneous distributed databases. Epsilon serializability allows for more concurrency by permitting non-serializable interleavings of database operations among epsilon transactions. We first present a strict 2-phase locking divergence control algorithm and an optimistic divergence control algorithm for a homogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction are the same. In such an environment, the total inconsistency of a distributed epsilon transaction is simply the sum of those of all its sub-transactions. We then describe a divergence control algorithm for a heterogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction may not be the same and the total inconsistency of a distributed epsilon transaction may be greater than the sum of those of all its sub-transactions. As a result, in addition to executing a local divergence control algorithm in each site to maintain the local inconsistency, a global mechanism is needed to take into account the additional inconsistency

Global query management in heterogeneous distributed database systems

Global query management provides the ability to combine data from different local databases in a single retrieval operation. The necessity for global query management arises in an open, heterogeneous multidatabase system, since autonomy and heterogeneity of component databases have given rise to a number of new major issues regarding the global query optimization strategy and context mediation including data conversion and query translation. For instance, some local DBMSs never support semijoin operator which has been proposed in order that data transmission between sites could be reduced. In this regard, the global query optimization strategies developed for homogeneous distributed database systems make extensive use of semijoins which are not attractive in the multidatabase context since this may increase the local processing time. Moreover, these do not consider the cost incurred as a result of data conversion and query translation. Our basic principle to get a high performance is that we decompose a global query to the finest level of subqueries in order to explore all possible execution plans. This reduces the overall processing cost in an heterogeneous distributed database system because subqueries that are sent to the local databases have to be converted. The lesser number of subqueries implies less conversion cost.

Development of an autonomous heterogeneous distributed database system: DHIM

In this paper, we design and implement a prototypical heterogeneous distributed database system, named DHIM (Distributed Heterogeneous Information Management). The objectives of DHIM are two-fold: one is to realize the global update synchronization mechanism which preserve the global serializability of concurrent executions and the local site autonomy in tightly coupled heterogeneous distributed database systems, and the other is to implement an open architectural distributed database system. The open architecture implies that DHIM is able to operate independently from the features of element local database systems. Therefore, any database system can be federated into DHIM as an element database system.

An integrated access control in heterogeneous distributed database systems

As a number of diverse, heterogeneous types of database management systems are employed within a single organization, the need to integrate those systems is stringent to have an efficient and transparent accesses to remote sites. Of our particular interest among various heterogeneity issues is integrated access control that combines mandatory access control (MAC) and discretionary access control (DAC) together, with MAC based on a lattice of sensitivity labels and DAC based on individual and group access privileges. The necessity for integrating MAC and DAC arises in an open, heterogeneous multidatabase system, since any trusted system has so far provided a single, exclusive type of access control paradigm: either MAC or DAC. In this paper, we tried to formulate an integrated access control, which can provide a new and general framework to access control in heterogeneous distributed database systems (HDDBSs). The integrated access control, placed at the level of global data manager in each site, is used for security enforcement in an HDDBS. The global data manager maintains a data dictionary that contains meta data describing the global schema of the multilevel databases, clearances of users, security classifications of data, and access authorizations. Our integrated access control restricts both access to information and the flow of information only in authorized ways.

Update synchronization pursuing site autonomy in heterogeneous distributed databases

Although many researches in distributed database area perceive that the only practical way to construct a distributed database system from already existing local heterogeneous database systems is to integrate them by guaranteeing local site autonomy, an efficient update synchronization scheme for the system has not been developed so far. Furthermore, most previous concurrency control schemes for heterogeneous systems failed to guarantee site autonomy or global serializability. In this paper, we propose a concurrency control scheme that guarantees both global serializability of concurrent transaction execution and site autonomy for heterogeneous distributed database systems.

Distributed management of transactions in heterogeneous distributed database systems

In the two phase commit protocol, the coordinator decides to commit the distributed transaction if all its subtransactions are in a state called the “prepared state”. We have increased the semantics of the two phase commit protocols by replacing the prepared state by more restrictive states called the “source state” and the “serializable state”. The source state ensures that the execution of committed distributed transactions is not only atomic but also serializable. It also ensures that distributed transactions cannot interfere with other distributed transactions through local transactions, but it does not ensure a serializable view of the distributed database if local transactions are taken into account. The serializable state ensures that the execution is serializable also if local transactions are taken into account. Which of the two correctness criteria is appropriate for global concurrency control depends on the distributed applications of the system. In the proposed mechanism, each interconnected site supports the source state or the serializable state. Various methods of supporting these states are presented. Which method is appropriate for a site depends on the concurrency control method and the autonomy requirements of the site.

Global checkpointing scheme for heterogeneous distributed database systems

We propose a transaction-consistent checkpointing scheme for heterogeneous distributed database systems. Using the global checkpoints generated by the checkpointing scheme, the heterogeneous distributed database system can efficiently reconstruct the database to the most recent consistent state from media failures. The checkpointing scheme never enforces termination of normal operations of transactions and changes of checkpointing schemes in local database management systems. Thus, the checkpointing scheme guarantees the design autonomy of local database management systems and increases the availability on the heterogeneous distributed database systems.

Design and implementation of a heterogeneous distributed database system

This paper introduces a heterogeneous distributed database system called LSZ system, where LSZ is an abbreviation of Li Shizhen, an ancient Chinese medical scientist. LSZ system adopts cluster as distributed database node (or site). Each cluster consists of one or several microcomputers and one server. The paper describes its basic architecture and the prototype implementation, which includes query processing and optimization, transaction manager and data language translation. The system provides a uniform retrieve and update user interface through global relational data language GRDL.

Heterogeneous distributed database systems for production use

It is increasingly important for organizations to achieve additional coordination of diverse computerized operations. To do so, it is necessary to have database systems that can operate over a distributed network and can encompass a heterogeneous mix of computers, operating systems, communications links, and local database management systems. This paper outlines approaches to various aspects of heterogeneous distributed data management and describes the characteristics and architectures of seven existing heterogeneous distributed database systems developed for production use. The objective is a survey of the state of the art in systems targeted for production environments as opposed to research prototypes.

DATAPLEX: an access to heterogeneous distributed databases

Diverse database management systems are used in large organizations. The heterogeneous distributed database system (DDS) can provide a flexible intergration of diverse databases for users and applications. This is because it allows for retrieval and update of distributed data under different data systems giving the illusion of accessing a single centralized database system.