Transparency is one of the advantages of distributed database systems (DDBMS), so what is transparency in DDBMS? This article will introduce you to transparency in DDBMS and introduce the types of transparency. I hope it will be helpful to you.
What is transparency in DDBMS?
Transparency is a property of distributed databases that is used to hide the internal details of a DDBMS distribution from users and does not allow users to view the internal details of the distribution.
The reason transparency is important is usability. The more transparent our systems are, the less cognitive load there is on users. In other words: transparency simplifies the system's API.
For example: A DDBMS designer may choose to fragment a table, copy the fragments and store them in different sites. However, since users do not understand these details, they find distributed databases easy to use, just like any centralized database.
Types of transparency in DDBMS
DDBMS can provide various levels of transparency, which are mainly divided into four main types of transparency:
● Distribution transparency
● Transaction transparency
● Performance transparency;
● DBMS transparency.
Here's an introduction:
Distribution Transparency
##Distribution transparency allows users to treat the database as a single logical entity. If a BMS is added to display distributed transparency, the user does not need to know whether the data is a detail (fragment transparency) or the location of the data item (local transparency). Distribution transparency can also be divided into the following levels:1. Fragmentation transparency:
Fragmentation is the highest level of distribution transparency. If the DDBMS provides fragmentation transparency, the user does not need to know that the data is fragmented, therefore, database access is based on the global schema. Users can access any table in a non-fragmented manner. Information that the table is segmented and the location of the segments across multiple sites is hidden from the user. SQL views work in a similar way, where the user is unaware of the fact that the user is viewing a view of a table and not the original table.2. Position transparency:
Position is the middle level of distribution transparency. With location transparency, users can query any table or fragment of a table as if they were stored locally in the user's site, but without having to know the location of the data. The fact that its tables or fragments of them are stored at a remote site in a distributed database system should be completely disregarded by end users. The address and access mechanism of the remote site are completely hidden. To incorporate location transparency, the DDBMS should have access to updated and accurate data dictionaries and DDBMS catalogs containing details of data location.3. Replication transparency:
Hide database replication from users through replication transparency. Users can access any table as the original table. When a user updates data, it is updated and reflected in all tables across multiple sites. This is hidden from the user and is called concurrency transparency. Replicating a copy makes it easier for users to continue querying in the event of a site failure without being aware of the failure, which is called failure transparency.4. Local mapping transparency:
It is the lowest level of distribution transparency. With local mapping transparency, the user needs to specify the fragment name and location of the data item, taking into account any duplication that may exist. Obviously, this is a more complex and time-consuming query for the user than the first one. Systems that provide this level of tr_sparency are unlikely to be accepted by end users.Transaction Transparency
Transaction transparency in a DDBMS environment ensures that all distributed transactions maintain the integrity and consistency of the distributed database. Distributed transactions access data stored in a remote location. Each transaction is divided into several sub-transactions, each corresponding to a site that must be visited; the sub-transactions are represented by agents. DDBMS must also ensure the atomicity of each sub-transaction. Fragmentation, allocation and replication schenlas complicate transaction transparency in distributed DBMS.Performance Transparency
Performance transparency requires that the DDBMS perform like a centralized DBMS. In a distributed environment, the system should suffer any performance degradation due to the distributed architecture, such as the presence of a network. Performance transparency also requires the DDBMS to determine the most cost-effective strategy for executing requests. In a centralized DBMS, the query processor (QP) must evaluate each data request and find the optimal execution strategy, which consists of an ordered sequence of operations on the database. In a distributed environment, the Distributed Query Processor (DQP) maps data requests to an ordered sequence of operations on a local database. Added complexity takes into account fragmentation, copying and allocation patterns.DQP must decide:
● Which fragment should be accessed?● If a fragment is copied, which fragment copy should be used?
● The location used.
DQP produces an execution policy optimized for some cost function. Typically, the costs associated with distributed requests include:
● The access time (I/O) cost involved in accessing physical data on disk;
● Performing on data in main memory The CPU time cost incurred during operation;
● The communication cost associated with transmitting data over the network.
The first two factors are the only factors considered in a centralized system. In a distribution environment, DDBMS must consider communication costs, which may be the most dominant factor in WANs with bandwidths of several kilobytes/second. In this case, optimization may ignore I/O and CPU costs. However, the bandwidth of a LAN is comparable to that of a disk, so optimization should not completely ignore I/O and CPU costs in this case.
DBMS transparency.
DBMS transparency hides the knowledge that the local DBMS may be different and therefore only works with heterogeneous DDBMS. It is one of the hardest forms of transparency to provide.
The above is the entire content of this article, I hope it will be helpful to everyone's study. For more exciting content, you can pay attention to the relevant tutorial columns of the PHP Chinese website! ! !
The above is the detailed content of What are the types of transparency in DDBMS?. For more information, please follow other related articles on the PHP Chinese website!

本篇文章给大家带来了关于mysql的相关知识,其中主要介绍了关于索引优化器工作原理的相关内容,其中包括了MySQL Server的组成,MySQL优化器选择索引额原理以及SQL成本分析,最后通过 select 查询总结整个查询过程,下面一起来看一下,希望对大家有帮助。

win10系统有许多比较新颖的功能,有小伙伴想要让自己的win10系统更加具有个性化,因此想设置任务栏透明度看起来更加酷炫些。那么win10任务栏如何设置透明度呢?下面小编就教下大家win10任务栏设置透明度的方法。具体的方法如下:1、打开电脑,鼠标移动到任务栏,然后鼠标右键任务栏,在窗口找到“任务栏设置”并且点开。2、点开“任务栏设置”窗口后,找到“颜色”选项,点开,在“颜色”设置界面可以设置大家所喜欢的得任务栏颜色,大家可以选择Windows颜色也可以自定义颜色,选好颜色后找到下面的“透明效

数据库系统由4个部分构成:1、数据库,是指长期存储在计算机内的,有组织,可共享的数据的集合;2、硬件,是指构成计算机系统的各种物理设备,包括存储所需的外部设备;3、软件,包括操作系统、数据库管理系统及应用程序;4、人员,包括系统分析员和数据库设计人员、应用程序员(负责编写使用数据库的应用程序)、最终用户(利用接口或查询语言访问数据库)、数据库管理员(负责数据库的总体信息控制)。

我们平时在制作ppt的时候可以给图片穿插到里边,但是PPT怎么设置图片透明度这个问题对于一些刚学的小伙伴们还是不知道怎么实现,那么今天我就来教大家具体的操作步骤,具体步骤如下图。1.首先,在电脑上打开并且新建一个PPT文档,(如下图所示)。2.接下来,在上方工具栏中选择【插入】-【形状】,选择矩形并在空白画布上画出,(如下图红色圈出部分和红色箭头指向所示)。3.然后,在上方工具栏中选择【填充】,(如下图红色圈出部分和红色箭头指向所示)。4.接下来,在【填充】对话框中选择【更多设置】,(如下图红色

CSS属性实现透明度渐变效果的方法,需要具体代码示例在网页设计中,透明度渐变效果可以为页面增添一种柔和而美观的过渡效果。通过CSS属性的设置,我们可以轻松实现不同元素在透明度上的过渡效果。今天我们就来介绍一些常见的方法和具体的代码示例。使用opacity属性Opacity属性可以设置元素的透明度,取值范围从0到1,0表示完全透明,1表示完全不透明。我们可以通

醒图透明度在“特效->调节参数”中,其设置图片透明度的具体方法是:1、打开醒图app;2、点击“导入”,选择“喜欢的图片”打开;3、在页面底部找到并点击“特效”,然后点击“调节参数”,点击“透明度”,滑动刻度线即可设置透明度。

数据库的“完整性”是指数据的正确性和相容性。完整性是指数据库中数据在逻辑上的一致性、正确性、有效性和相容性。完整性对于数据库系统的重要性:1、数据库完整性约束能够防止合法用户使用数据库时向数据库中添加不合语义的数据;2、合理的数据库完整性设计,能够同时兼顾数据库的完整性和系统的效能;3、完善的数据库完整性有助于尽早发现应用软件的错误。

mysql查询为什么会慢,关于这个问题,在实际开发经常会遇到,而面试中,也是个高频题。遇到这种问题,我们一般也会想到是因为索引。那除开索引之外,还有哪些因素会导致数据库查询变慢呢?


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Dreamweaver CS6
Visual web development tools

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool
