Transcript Distributed DBMS Architecture

Distributed DBMS
Architecture
Chapter 4
Principles Of Distributed Database
Systems,2/e By Ozsu, Patrick
Valduriez
Distributed DBMS Architecture
Architecture of a systems
defines its structure, means, the
components of the systems,
function performed by each
component and the relationship
among components
BZUPAGES.COM
• Three major architectures of
DDBMS discussed
–Peer to peer
–Client/Server
–Multdatabase
• These are idealized architectures,
practical installations may wary
BZUPAGES.COM
DBMS Standardization
A conceptual framework whose
purpose is to divide
standardization work into
manageable pieces and to show
at a general level how these
pieces are related to one another.
Approaches
BZUPAGES.COM
• Component-based Components
of the system are defined
together with the
interrelationships between
components. Good for design and
implementation of the system.
However it is difficult to determine
functionality of system by seeing
its individual component
BZUPAGES.COM
• Function-based Classes of users
are identified together with the
functionality that the system will
provide for each class. The
objectives of the system are
clearly identified. But how do you
achieve these objectives?
BZUPAGES.COM
• Data-based Identify the different
types of describing data and
specify the functional units that
will realize and/or use data
according to these views
BZUPAGES.COM
Practically
• Every aspect has to be considered
• These Classification schemes are
Orthogonal
• A committee for the DBMS
standardization was established in
1972 by ANSI under SPARC
(Standards Planning and
Requirement Committee)
BZUPAGES.COM
• Published its initial report in 1975
and then in 1977
• Its full name being
“ANSI/X3/SPARC DBMS
Framework”
• Mainly based on Data
organization
BZUPAGES.COM
Reference Model
Users
External Schema
External
View
Conceptual Schema
Internal Schema
BZUPAGES.COM
External
View
Conceptual
View
Internal
View
External
View
Dimensions for DDBS Architecture
Autonomy refers to the distribution of
control not of data. It indicates the
degree to which individual DBMSs can
operate independently. Types could be
Design, Communication and
Execution Autonomy. Degree of
Autonomy varies in different DDBS
architectures
BZUPAGES.COM
Distribution deals with data.
Logically, data appears to be
placed at a single place but
practically it may be spread at
physically different locations
BZUPAGES.COM
Heterogeneity refers the
differences in hardware and
software among the individual
databases. Like different
machines, OS, Data Models,
DBMSs, or query languages
BZUPAGES.COM
BZUPAGES.COM
Major DDBS Architectures-I
1.Client-Server Architecture
– The term used in different meanings;
generally C and S refer to
processes, may be running at the
same machines
– In the context of DDBS both client
and server are machines not
processes (Fig 4.4)
– Server performs most of the data
Management;
• Query Processing
BZUPAGES.COM
• Transaction and Storage Management
Major DDBS Architectures-I &
II
–Client passes user queries to server
without trying to understand or
optimize them
–One Server Multiple Clients
–Multiple Servers
• One Server at a time
• Multiple Servers (transparently) at a time (A DDBS)
2- Peer to Peer Distributed
Systems
• Heterogeneous databases at each
site,
defining Local Internal Schemas
BZUPAGES.COM
Interpreting user commands
and formats results
Checks if user query can be
processed
Optimized execution strategy
Global queries to local ones
Coordinates distribution
execution of user requests
BZUPAGES.COM
Chooses best access path to
any data item
Makes sure the consistency of
local data even in case of
failure
Physically accesses the data as
per the commands generated
by query optimizer. Interacts
with the OS
BZUPAGES.COM
Major DDBS Architectures-III
A Multidatabase System
• Provides access from multiple,
autonomous heterogeneous, and
distributed databases. Two Major
architectures:
•
•
Global Schema Architecture
Federated Schema Architecture
BZUPAGES.COM
Multidatabase Systems: Architectures
External
Schema
External
Schema
External
Schema
External
Schema
Federated
Schema
Global
Schema
Federated
Schema
Schema Integration
Export
Schema
Component
Schema
•••
Export
Schema
Export
Schema
Export
Schema
Component
Schema
Component
Schema
•••
Component
Schema
Schema Translation
Local
Schema
Local
Schema
•••
Global Schema Architecture
BZUPAGES.COM
Local
Schema
Local
Schema
•••
Federated Database Architecture
Global Directory Issues
• A directory is a database that contains data
about data (meta-data). Called global
directory in case of a DDBS. Three issues;
• A single large or local for each site
• Location; whether to keep at a single site or
distributed.
• Single copy or replication
• All three issues are orthogonal to each other
• That concludes chapter 4, questions?
BZUPAGES.COM
Distributed database environments (adapted from Bell and
Grimson, 1992)
BZUPAGES.COM
Distributed Database Options
• Homogeneous - Same DBMS at each node.
– Autonomous - Independent DBMSs.
– Non-autonomous - Central , coordinating DBMS.
• Heterogeneous - Different DBMSs at different
nodes.
– Gateways - Simple paths are created to other databases
without the benefits of one logical database.
BZUPAGES.COM
Distributed Database Options
– Systems - Supports some or all of the
functionality of one logical database.
• Full DBMS Functionality - All dist. Db functions.
• Partial-Multi-database - Some dist. Db functions.
–Federated - Supports local databases
for unique data requests.
» Loose Integration - Local dbs have their own schemas.
» Tight Integration - Local dbs use common schema.
–Unfederated - Requires all access to go
through a central, coordinating module.
BZUPAGES.COM
Homogeneous, NonAutonomous
Database
• Data is distributed across all the nodes.
• Same DBMS at each node.
• All data is managed by the distributed
DBMS (no exclusively local data.)
• All access is through one, global schema.
• The global schema is the union of all the
local schema.
BZUPAGES.COM
Focus on The Following
Heterogeneous Environment
• Data distributed across all the nodes.
• Different DBMSs may be used at
each node.
• Local access is done using the local
DBMS and schema.
• Remote access is done using the
global schema.
BZUPAGES.COM