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This article will explain in detail what the transparency in DDBMS is. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

What is transparency in DDBMS?

Transparency is an attribute of the distributed database that hides the internal details of the DDBMS distribution from the user and does not allow the user to view the internal details of the distribution.

The reason why transparency is important is availability. The higher the transparency of our system, the less the cognitive burden on users. In other words: transparency simplifies the API of the system.

For example, DDBMS designers can choose to segment tables, copy fragments, and store them in different sites. However, because users do not know 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, mainly divided into four main types of transparency:

● Distribution Transparency

Transparency of ● transaction

● performance transparency

● DBMS transparency.

Here's an introduction:

Distribution transparency

Distribution transparency allows users to treat the database as a single logical entity. If you add a BMS to display distribution transparency, the user does not need to know whether the data is detailed (fragment transparency) or the location of the data item (local transparency).

Distribution transparency can also be divided into the following levels:

1. Crushing transparency:

Fragmentation is the highest level of distribution transparency. If DDBMS provides fragmentation transparency, users do not need to know that the data is fragmented, so database access is based on global schema.

Users can access any table in a non-segmented manner. The information in which the table is segmented and the location of fragments on multiple sites are hidden from the user.

The SQL view has a similar manner in which the user does not know the fact that the user is viewing the view of the table rather than the original table.

2. Location transparency:

The 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 do not have to know the location of the data.

The fact that its table or its fragments are stored at a remote site in a distributed database system should completely ignore the end user. The address and access mechanism of the remote site are completely hidden.

To incorporate location transparency, DDBMS should be able to access updated and accurate data dictionaries and DDBMS directories that contain details of the data location.

3. Copy transparency:

Hide the replication of the database from the user through replication transparency. Users can access any table as the original form.

When the user updates the data, it updates and is reflected in all tables at multiple sites. This is hidden from the user, which is called concurrent transparency. Replicas make it easy for users to continue to query in the event of a website failure without knowing the failure, which is called fault transparency.

4. Transparency of local mapping:

It is the lowest level of transparency for distribution. With local mapping transparency, the user needs to specify the fragment name and the location of the data item, while considering any replication 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 the DDBMS environment ensures that all distributed transactions maintain the integrity and consistency of the distributed database. Distributed transactions access data stored far away from one location. Each transaction is divided into several sub-transactions, each of which corresponds to a site that must be visited; the sub-transaction is represented by the agent.

DDBMS must also ensure the atomicity of each child transaction. Fragmentation, allocation, and replication of schenlas complicates transaction transparency in distributed DBMS.

Performance transparency

Performance transparency requires DDBMS to perform like a centralized DBMS. In a distributed environment, the system should suffer any performance degradation due to the distributed architecture, for example, the existence of the network performance transparency also requires DDBMS to determine the most cost-effective strategy to execute the request.

In a centralized DBMS, the query processor (QP) must evaluate each data request and find the best 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 ordered sequences of operations on the local database. Taking into account fragmentation, replication and distribution patterns, adds complexity. DQP must decide:

Which clip does ● want to visit?

● if the fragment is copied, which copy of the fragment will be used?

The location used by ●.

DQP produces an execution strategy that is optimized for some cost functions. Typically, the costs associated with distributed requests include:

Access time (I / O) cost involved in ● accessing physical data on disk

CPU time cost incurred by ● when performing operations on data in main memory

The communication costs associated with the transmission of data over the network for ●.

The first two factors are the only factors considered in a centralized system. In a distribution environment, DDBMS must take into account communication costs, which may be the most important factor in a WAN with a bandwidth of several thousand bytes per second. In this case, optimization may ignore I / O and CPU costs. However, the bandwidth of LAN is equal to that of disk, so in this case, optimization should not completely ignore I / O and CPU costs.

DBMS transparency.

DBMS transparency hides knowledge that local DBMS may be different, so it only applies to heterogeneous DDBMS. It is one of the most difficult transparency to provide.

About what transparency in DDBMS is shared here, I hope the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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