Download CHAPTER 25 - Distributed Databases and Client*Server Architectures

GROUP MEMBERS
Edwin Acquah
Andria Akua Abraham
Henry Cleland
Francis Asante
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Introduction and Concepts
Types of DDBMS
Techniques for DDBMS Implementation
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Fragmentation
Replication
Query Processing
Concurrency
Architecture
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DDB Technology is a merger between
 Database
Technology
 Networks and Data Communication
Technology
However, developments have been shifted from Pure DDBMS
products to
 Systems based on Client-Server Architectures or
 Developing Technologies for accessing Distributed
Heterogeneous Data sources
 Decentralizing
Of Processing (at the
system level) while achieving an
Integration of Information sources (at
the logical level) within a
geographically distributed systems of
databases, applications and users
 Management
of distributed data
with different levels of transparency
 Increased reliability and availability
 Improved performance
 Easier expansion
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Ability to keep track of the data distribution,
fragmentation, and replication by expanding
the DDBMS catalog.
Ability to access remote sites and transmit
queries and data among the various sites via
a communication network.
Executed with the proper management of the
security of the data and the authorization
/access privileges of users.
Degree of homogeneity
Degree of local autonomy
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Each server is an independent and
autonomous centralized DBMS.
Used when there is a global view or schema
of the federation of databases that is shared
by the applications.
In heterogeneous FDBS one server may be a
relational DBMS, another a network DBMS
and the third an object or hierarchical DBMS.
 Differences
in data models
 Differences
in constraints
 Differences
in query languages
The universe of discourse from which the
data is drawn
 Representation and meaning
 The understanding, meaning and
subjective interpretation of data
 Transaction and policy constraints
 Derivation of summaries
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 Communication
autonomy
 Execution autonomy
 Association autonomy.
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Fragmentation
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Replication
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Vertical Fragmentation (PROJECTION)
Horizontal Fragmentation (SELECT)
Mixed(Hybrid) Fragmentation
Global catalog schema
Degree of replication
Query Processing
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Query Decomposition
Semijoins
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Issues that arise include:
Dealing with multiple copies of data items
 Failure of individual sites
 Failure of communications links
 Distributed commit
 Distributed DEADLOCK
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Based on an extension of centralized locking.
Idea is to designate a particular copy of each
data item as a distinguished copy.
Locks for that data item deal with the
distinguished copy as such all locking and
unlocking requests are sent to the site that
contains that copy.
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Primary site technique (Coordinator site)
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All distinguished copies are kept on one site.
Risk and impact of failure is high
Primary Site with Backup
-Adds a backup site to curb the high risk of failure.
Primary copy technique
-distribute locks over several sites
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Presentation layer
Application layer
Database sever
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Distribution transparency