Distributed database transparency features
DDBMS transparency features have the common property of allowing the end user to feel like the database s only user . In other words, the user believes that (s)he is working with centralized DBMS; all complexities of a distributed database are hidden ,or transparent to the user.
The DDBMS transparency features are:
• Distribution transparency ,which allows a distributed database to be treated as a single logical database. If a DDBMS exhibits distribution transparency , the user does not need to know:
- That the data are partitioned _ meaning the table s rows and columns
are split vertically or horizontally and stored among multiple sites.
- That the data can be replicated at several sites.
- The data location.
• Transaction transparency, which allows a transaction to update
data at more than one network site Transaction transparency ensures
that the transaction will be either entirely completed or aborted. Thus,
maintaining database integrity.
• Failure transparency. which ensures that the system will continue
to operate in the event of a node failure. Functions that were lost
because of the failure will be picked up by another network node.
• Performance transparency. which allows the system to perform as if
it were a centralized DBMS. The system will not suffer any performance
degradation due to its use on a network or due to the network s
platform differences. Performance transparency also ensures that
the system will find the most cost-effective path to access remote
data.
• Heterogeneity transparency. Which allows the integration of several
different local DBMSs (relational. network, and hierarchical) under a
common, or global, schema. The DDBMS is responsible for translating
the data requests from the global schema to the local DBMS schema.
DISTRIBUTION TRANSPARENCY
The level of transparency supported by the DDBMS varies from system to system. Three levels of distribution transparency are recognized:
• Fragmentation transparency is the highest level of transparency. The end user or programmer does not need to know that a database is partitioned. Therefore, neither fragment names nor fragment locations are specified prior to data access.
• Location transparency exists when the end user or programmer must specify the database fragment name but does not need to specify where those fragments are located.
• Local mapping transparency exists when the end user or programmer must specify both the fragment names and their locations.
Transparency features are summarized in the following Table
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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