3 levels of database architecture

8/6/2019 3 Levels of Database Architecture

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Distributed Database SystemsAutumn, 2007

Chapter 4

Distributed DBMS

Architecture

1Distributed Database Systems


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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

2Distributed Database Systems


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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.

Distributed Database Systems 3


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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


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)


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


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


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


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?


3 levels of database architecture

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