Distributed information sys
Post on 09-Dec-2014
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By : Ms.Meena Chauhan, M.Tech CSE
Sr.A.P.,ABES Engg College,Ghaziabad
Distributed Information Systems
Distributed Information Systems
Distributed Information System (DIS) is seen as a collection of autonomous in formation
systems which can collaborate with each other. This collaboration can be driven by requests for knowledge needed to predict what values should
replace null values in missing or incomplete attributes.
Distributed Information Systems
Distributed information system is a system that connects a number of
information systems using network communication technology. It is
assumed that DIS is autonomous and incomplete .
Distributed development of software and information systems (also named Global
Software Development) becomes increasingly common, driven by the
globalisation ofcompanies and their business and enabled
by new information and communicationtechnologies.
DISD
Distributed Information Systems Development (DISD) promotes realisation of IS in a collaborative way where several partners, generally situated in distant places, participate in the elaboration of a common solution. The DISD consists in decomposing, the IS development process into more or les autonomous phases to be realised by these partners.
DISD aims at increasing enterprise productivity, reducing IS development cost, and enlarging the number of human competencies and skills, which allows not only to share experiences in different cultural environments but also to extend enterprise strategy to the global market. In fact, this kind of practice allows enterprises to deal with new economic globalisation constraints that they have to undergo but it is not devoid of problems.
It is clear that the distribution of processes has an impact on the way the IS products will be specified, designed, coded and delivered to the clients.
Design and related Aspects
Layers of an ISExample
presentation layer
application locic layer
resource management layer
client
info
rmati
on sy
stem
<html>...</html>
browser
Presentation Layer
● here is decided HOW data should appear to the user
Application Logic Layer
● Data Processing ('The actual Program')● here the algorithms are implemented● this Layer is often referred to as
– services– business logic– business rules– server
Resource Management Layer
● deals with and implements different data sources of IS
● is the 'data layer' in a restricted interpretation (Database Management System)
● can also be an external system, which recursively uses other ISs
Designs of IS
● top-down design
● bottom-up design
top-down design
● starts with defining functionality desired by the client ('toplevel goals')
● implementation of application logic● defining the resources needed by applictation logic
top-down [example] top-down design
1. define access channels and client platforms
2. define presentation formatsand protocols for the selectedclients and protocols
3. define the functionality necessary to deliver the contentsand formats needed at the presentation layer
4. define the data sources and dataorganization needed to implementthe application logic
client
presentation layer
resource management layer
application logic layer
info
rmat
ion
syst
em
top-down design
● usually created to run in homogenous environments
● way of distribution has to be specified● results in tightly coupled components:
– functionality of each component heavily depends on functionality of other components
– design is component based, but components are not standalone
advantages & disadvantages
● advantages:– design emphasises final goals of the system– can be optimized for: functional and non-
functional(performance, availability,..) issues● disadvantages
– can only be designed from scratch– legacy systems cannot be integrated
today few ISs are designed purely top-down
bottom-up design
● fig 1.4
bottom-up design1. define access channels and client plattforms
2. examine existing resources and the functionality they offer
3. wrap existing resources andintegrate their functionality intoa constistent interface
4. adapt the output of the application logic so that it can be used with the required accesschannels and client protocols
client
presentaion layer
resource management layer
application logic layer
info
rmat
ion
syst
em
bottom-up design
● out of necessity rather than choice● need to integrate legacy systems and/or
applications● results in loosely coupled systems
– independent and– standolone components
● most distributed IS are result of a bottom-up design
● Web services can make those designs more efficient, cost-effective and simplier to design
Architecture of an Information System - 4 types:
● 1 – tier, 2 – tier, 3 – tier,.......,n – tier
1 – tier Architectures
● were used decades ago..● monolithic Information Systems● presentation, application logic, and resource
management were merged into a single tier● many of these 'old' Systems are still in use!
Design of 1 – tier Architecture
[figure 1 – tier]presentation layer
application locic layer
resource management layer
client
info
rmat
ion
syst
em
1 – tier Architecture
advantages:● easy to optimize performance● no context switching● no compatibility issues● no client developement, maintainance and
deployment costdisadvantages:● monolithic pieces of code (high maintainance)● hard to modify● lack of qualified programmers for these systems
2 - tier Architectures
● fig 1.7 p.12
client
info
rm
ati
on
sy
ste
m
resource management layer
application logic layer
serv
er
presentation layer
2 - tier Architectures
● separation of presentation layer from other 2 layers (app + resource)
● became popular as 'server/client' systems● thin clients/fat clients● RPC (Remote Procedure Call)● API (Application Program Interface)● need for standardization
advantages & disadvantages
advantages● portability● no need for context switches or calls between
component for key operationsdisadvantages● limited scalability● legacy problems (blown up clients)
3 - tier Architectures
● fig 1.10 p. 16
info
rmati
on
sy
stem
resource management layer
application logic layer
middleware
client
presentationlayer
3 - tier Architectures
● can be achieved by separating RM (resource management) from application logic layer
● additional middleware layer between client and server– integration logic– application logic
● lead to the introduction of clear RM layer interfaces
● good at dealing with intgration of different resources
3 - tier
● fig 1.11 p. 17presentation layer
client
integration logic
client client
application logic layer
middle-ware
wrapper wrapperwrapper
1 - tier 2 - tier 3 - tier
resource managementlayer
advantages & disadvantages
advantages● scalability by running each layer on a different
server● scalability by distributing AL (application logic
layer) across many nodes ● additional tier for integration logic● flexibilitydisadvantages● performance loss if distributed over the internet● problem when integrating different 3 – tier
systems
2 cases of n – tier● systems linked with added connectivity through
the internet● resource layer is a full fledged 2 - or 3 - tier
system
n -tier
n -tier
● fig 1.12 p. 20
info
rmati
on s
yst
em
resource management layer
Web server
HTML filter
presentation layer
Web browser
client
application logic layer
middleware
n - tier
● [fig 1.13 p. 21]
databaseserver
applicationfileserver
middlewareapplication
logic
middlewareapplication
logic
additional RM layers
middlewareapplication
logic
internalclients
Web servercluster
LANgateways
FIREWALL
INTERNET
remoteclient
remoteclient
remoteclient
remoteclient
remoteclient
remoteclient...
advantages & disadvantages
advantages● better scalability● higher fault tolerance● higher throughput for less costdisadvantages● too much middleware involved ● redundant functionality● difficulty and cost of developement
gains and losses
with growing number of tiers one gains:● flexibility● functionality● possibilities for distributionbut:● each tier increases communication costs● complexity rises● higher complexity of management and tuning
communication in an IS between distributed layers/tiers
● synchronous interactions● asynchronous interactions
synchronous interactions (blocking)
● fig 1.14 p. 23invoking execution thread
invoked execution thread
request
response
blo
ckin
g p
erio
d
asynchronous interactions (non blocking)
● fig 1.15 p. 25invoking execution thread
invoked execution thread
put
put
fetch
fetch
queue
queue
thre
ad r
emai
ns
acti
ve
scaling multi tier systems
6 steps● understand the application environment● categorize your workload● determine the components most impacted● select scaling techniques to apply● apply the techniques● reevaluate● .. and hope its better :)
what do scaling techniques improve?
scaling technique
use faster machine x
create machine cluster x
use a special machine x x
segment the work load x x
batch request x
aggregate user data x
manage connections x
cache data & requests x x
increase capacity/ speed
improve efficiency
shift/reduce load
use faster machine
● increases the ability to do more work in a unit of time by processing tasks more rapidly
● applies to almost all parts of the system (from edge servers to database server)
create cluster of machines
● services more client requests. improves response time through parallelism
● applies to Web presentation server, Web application server, directory and security servers
use special machines
● improves efficiency of a component by using a special purpose machine, which is optimized for a specific function
● applies to egde server, Web presentation server, directory and security servers, the network and the Internet firewall
segment the workload
● splits up workload into managable chunks to obtain more predictible response times
● applies to Web representation server, Web application server, the data server and the network
batch requests
● reduces number of requests by defining new ones that combine multiple requests
● applies to Web presentation server, Web application server, directory and security servers, existing business applications and database
aggregate user data
● allows rapid access to large customer data controlled by existing system applications by aggregating distributed customer data into a customer information service
● applies to the Web presentation server, Web application server and the network
manage connections
● minimizes number of connections and eliminates overhead of setting up connections by sharing a pool of preestablished connections between the layers
● applies to Web presentation server, Web aplication server and the database.
cache
● improves performance and scalability and response time by buffering data flows and reducing consumption of resources
● applies to the edge server, Web presentation server, Web application server, network, existing business applications and the database.
summary
● layers of an IS● designs of distributed IS● evolution of architectures and concepts● scaling techniques
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