Distributed information sys

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 information 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 of companies and their business and enabled by new information and communication technologies.

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.

Layers of an IS Example <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 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 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]

1 – tier Architecture advantages: easy to optimize performance no context switching no compatibility issues no client developement, maintainance and deployment cost disadvantages: monolithic pieces of code (high maintainance) hard to modify lack of qualified programmers for these systems

2 - tier Architectures fig 1.7 p.12

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 operations disadvantages limited scalability legacy problems (blown up clients)

3 - tier Architectures fig 1.10 p. 16

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

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 flexibility disadvantages 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

advantages & disadvantages advantages better scalability higher fault tolerance higher throughput for less cost disadvantages 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 distribution but: 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. 23

asynchronous interactions (non blocking) fig 1.15 p. 25

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?

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

Distributed information sys

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