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Client-Server and Distributed Data Bases - Coggle Diagram
Client-Server and Distributed Data Bases
Client-server approach
client
makes requests
server
performs requests and communicates results
advantages
flexibility
ease of maintaining and adapting a system
scalability
ability to add and remove capacity in small units
interoperability
ability systems to exchange and use software and data
Two-Tier Architecture
PC client
contains the presentation code and SQL statements
database server
processes the SQL statements and sends query results back
performs process management functions
advantages
simplest to implement
limitations
software maintenance can be difficult
utilizing new technology may be difficult
Three-Tier Architecture
add a middleware server
transaction-processing monitor
support more simultaneous connections
message-oriented middleware
provides more flexibility in the kinds of messages supported
add an application server for specific kinds of processing
limitations
not address division-of-processing concerns
Multiple-Tier Architecture
support additional layers of servers
can be invoked from
PC clients
middleware
database servers
provide a finer division of processing
can improve performance
Web Services Architecture
supports interaction between
service provider
owns the service
provides the computing platform offering the service
service requestor
searches for a service
uses the service after it is discovered
service registry
repository
Distributed Database Architecture
support global requests
queries that combine
data from more than one site
transactions that update data at more than one site
site
locally controlled computer with a unique network addres
local data manager
controls databases with sites
provide complete features of a DBMS
can be
homogeneous
heterogeneous
distributed data manager
optimizes query execution across sites
coordinates concurrency control and recovery across sites
controls access to remote data
can call internal components
access the internal state of local data managers.
Schema Architectures
tightly integrated distributed DBMS
contains
allocation layer
contains the location of each fragment
fragmentation layer
contains the definition of each fragment
fragment
can be defined as
vertical subset
project operation
horizontal subset
restrict operation
mixed fragment
combination of project and restrict operations
allocated to one site but sometimes to multiple sites
loosely integrated distributed DBMS
supports more autonomy of local database sites
local mapping schemas
support data sharing
describe the exportable data at a site
provide conversion rules to translate data
Distributed Query Processing
involves
both local
global optimization
involves data movement and site selection decisions
more complex because multiple optimization objectives exist
provides
concurrency
recovery transparency