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8/6/2019 3 Levels of Database Architecture
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Distributed Database SystemsAutumn, 2007
Chapter 4
Distributed DBMS
Architecture
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Introduction
Architecture defines a systems structure
with Components
Functions of components, and
Their interactions
Purpose of reference architecture:
A framework for discussion Standardization
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4.1 Transparencies in a distributed DBMS
X transparency means the existence of X
is not known to users. Closely related to architecture issues.
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4.1.1 Data independence
Same as in centralized DBMS:
Logical data independence applications are immune to changes in schema
Physical independence
applications are immune to changes in physicalstorage, and data distribution
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4.1.2 Network transparency Also known as distribution transparency
4.1.3 Replication transparency
4.1.4 Fragmentation transparency Data fragmentation the division of
relation into smaller fragments at different
sites.
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4.2 DBMS Standardization
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4.2.1 ANSI/APARC Architecture
A 3-level architecture based on data organization
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View DescriptionExternal View How users view the shared data
Commands used:
create view as
Conceptual View Synthesis of external views of an enterprise Commands used:
create db
create table
Internal View
Physical definition and organization of data Commands used:
index on device
segment definition and allocation
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The ASNI/SPARC Architecture (1997)
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External
View
External
View
External
View
Conceptual
View
Internal
View
External
Schema
Conceptual
Schema
Internal
Schema
Users
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4.3 Architecture Models for Distributed DDBMS
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4.3 Architecture Models for Distributed DDBMS
Classification of multiple DBs shared bymultiple DBMSs
Criteria for classification
Distribution
0: centralized, 1: C/S, 2: P2P
Autonomy
0: tight integration, 1: semi-autonomous, 2: total
isolation Heterogeneity
0: homogeneous, 1: heterogeneous
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Distribution
Autonomy
Heterogeneity
1. (A0,D2,H0)
P2P
homogeneous
tightlyintegrated
P2P
homogeneous
federated
P2P
homogeneous
multidatabase
2. P2P
heterogeneous
federated
3. (A2,D2,H1)
P2P
heterogeneous
multidatabase
Note 1: the available most advanced commercial product
2 and 3: active research area
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Autonomy: the distribution of control
(0) tightly integrated
a single image of the entire DB to and userand a single DBMS
(1) semi-autonomous
all DBMSs can operated independently buthave to join a federation to make local datasharable
(2) total isolation each DBMS is stand-alone and enjoy 100%
freedom of autonomy
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Distinction between DDB and MDB
In MDB
every local data manager is a complete DBMSwith its own DDL, DML and TM
In DDB
there is only one data manager with its
dependent component-data-manager at every
local site
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The focus of this course is the
PRINCIPLES of DDBs (A0, D2, H0)
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4.3.1 Distributed DBMS architecture
An architecture based on data organization
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External SchemaExternal Schema External Schema
Global Conceptual
Schema
Local Internal
Schema
Local Conceptual
Schema
Local Conceptual
Schema
Local Conceptual
Schema
Local Internal
Schema
Local Internal
Schema
ES
LCS
LIS
GCS
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Detailed functional description of DDBMS
Legend
Administrative Role
Data Dictionary/Directory
Processing Unit
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Enterprise
Administrator
Global DB
Administrator
Application
SystemAdministrator
GCS
Processor
ES
Processor
Local Data ManagerLocal Data Manager
Local
DBA
GCS
Processor-1
LD/D
Local IS
Processor
Internal
DB
Conceptual
Transformation
Int. Storage
Int. DB
Transformation
GD/D
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Components of a Distributed DBMS
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Semantic data controller
Integrity constraint and
authorization
Global Query Processor
decompose and optimize
global query
Global Execution Monitor
Distributed transaction
manager
Runtime Support Processor
physical access to database
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Client/Server
Systems
A computingmodel dividing
functions
between client
and server
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Discussion
Why DDB?
Compare DDB with CDB, MDB, C/S DB. Do you understand DDB architecture?
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