1. Distributed Systems: The Overall Architecture
Chapter 5
Information Systems Management in Practice
8th Edition

2. Outline & Objectives Introduction
Attributes of Enterprise Distributed Systems
Corporate Policy for Distributed Computing
Two Guiding Frameworks

3. Outline & Objectives Types of Enterprise Distributed Systems
Host-based Hierarchy
Decentralized Stand-Alone Systems
Peer-to-Peer LAN-Based Systems
Hybrid Enterprise-Wide Systems
Client-server Systems
Internet-Based Computing
Web Services

4. Introduction IT architecture versus IT infrastructure
Architecture (conceptual)
Blueprint
Infrastructure (physical)
Implementation (hardware, software, networks)
Evolution of Distributed Systems
Mainframe  Client-server  Web

5. Attributes of Distributed Systems
Degree to which a system is distributed is dependent on:
Where the processing is done
Spread out the workload to other machines
Requires system interoperability
interoperability is the ability of a system or a product to work with other systems or products without special effort on the part of the customer

6. Attributes of Distributed Systems
How processors and other devices are interconnected
Redundancy (at least one alternative route)
Where the information is stored
Distributed databases without duplication
What rules or standards are used
Need system-wide rules
Technical (if-then-else)
Management (e.g. security)

7. Corporate Policy for Distributed Computing
IS has to decide when and to what degree computing at the corporate level should be distributed.
Hardware, software, networking, processing, storage
Responsibility should not be placed on individual end users and departments

8. Corporate Policy for Distributed Computing
Rule of Thumb: Systems responsibilities should be distributed unless:
Operations are interdependent (ERP)
Businesses are homogeneous
Corporate culture does not support decentralization (not aligned)

9. Types of Enterprise Distributed Systems

10. Types of Enterprise Distributed Systems
Host-based Hierarchy
First data processing distributed system
Refers to any device that relies on the host computer (that is, the computer the device is attached to) to handle some operations. 
Master-slave architecture: a central mainframe at the top, PCs at the bottom, minicomputers in between.
Data could be stored at any level

11. Host-Based Hierarchy

12. Types of Enterprise Distributed Systems
Decentralized Stand-Alone Systems
“Islands of Computing” (not distributed really)
Holdover from the past where departments put in their own minicomputers with no intention of connecting them to the corporate host or to their departmental systems
A major goal in introducing ERP systems was to replace such disparate systems with a single platform of inner-connectable modules to serve these various functions

13. Decentralized Stand-Alone Systems

14. Types of Enterprise Distributed Systems
Peer-to-Peer LAN-Based Systems
No hierarchy or ‘superior’ computer
Peer-to-peer communications
Interconnecting LANs rather than hierarchical communications through a central hub
No superior computer

15. Peer-to-Peer LAN-Based Systems

16. Types of Enterprise Distributed Systems
Hybrid Enterprise-Wide Systems
Combination hierarchy (host-based, favored for corporate computing) and LAN-based (favored by departments) Connected via WANs
Link “automation islands”
Begin to automate business processes (cooperative processing)
Take advantage of specialized computer programs, while at the same time extending the usefulness of some legacy systems

17. Hybrid Enterprise-Wide Systems

18. Types of Enterprise Distributed Systems
Client-Server Systems
The ’90s version of distributed systems
Splits computing workload between client and server which answers the request
(P)resentation
(A)pplication
(D)ata
Three-tier architecture (another way to look at it)

19. Client-Server

20. Client-Server Computing

21. Client-Server Arrangements

22. An Aerospace Company Case example: Client-Server Systems
Application code on clients
Data on servers (remote management)
Communication Middleware between them
Data repository is key (metadata)
Object-oriented computing
Distributed function minimizes costs

23. An Aerospace Company

24. Benefits & Drawbacks of Client-Server Systems
Better access to information
Increases organizational flexibility
System scalability
allows new technology to be added more easily without affecting rest of system
Streamlines work flow between functional areas
Encourages people to work together via networks
Front-end empowerment (decision-making)
Shifts focus of computing to users
Add more nodes without much disruption to entire computing system
Does not have to go through corporate server

25. Benefits & Drawbacks of Client-Server Systems
No cost differential (with regard to mainframe systems) because they entail so much coordination
IS job more complex although it is easier for users
Add more nodes without much disruption to entire computing system
Does not have to go through corporate server

26. Types of Enterprise Distributed Systems
Internet-Based Computing
Extension of client-server (via Internet)
Network-centric computing = a computer and a cloud
Essential for ubiquitous computing
Ubiquitous computing: computing is made to appear anytime and everywhere
New ways of doing business
Updating new versions of software
‘One copy’ of software
Authorized software (firm and purchased)

27. Internet-Based Computing

28. IBM, Nokia and Sabre Project: Pervasive Computing
Case example: Internet-Based Computing
Real-time interactive travel services provided via the mobile phone using WAP.
XML (eXtensible Markup Language)
Connect Sabre’s online traveling system to Nokia’s wireless network and Internet-enabled phones.
Java applets
Deliver applications over Internet
WML (Wireless Markup Language):
Present XML information to mobile device

29. Types of Internet-Based Computing
Server-based Computing (Thinner Client)
Mobile workers and laptops
Applications can be securely accessed by any device and updated directly on the server
Applications and sensitive data reside on server
e.g. Citrix Server (remote desktop)
Easier management
Lower cost

30. 3i “Anytime, Anywhere” access to systems for investment professionals
Case Example: Server-Based Computing (mobile)
“Anytime, Anywhere” access to systems for investment professionals
Up-to-date information
Connect to Citrix server (application) over the Internet using secure modem service (VPN)
Arrangement allows for global expansion
Offices in 14 countries (2007)

31. Types of Internet-Based Computing
Peer-to-Peer Computing (P2P)
Task distributed to wide number of computers (peers) connected over the Internet
The Grassroots movement now taken seriously by some corporations
First popularized by Napster
Economics: How to make money?
Subscriptions, where people pay for access rather than for ownership

32. Types of Enterprise Distributed Systems cont’d
Web Services
Second-generation Internet-based distributed system
URLs embedded in software modules so they can be called upon to perform their function as a service via the Internet
e.g. Google Apps, SalesForce
Computer-to-computer use of the Internet (based on object-oriented tenets)
Now: “cloud computing” (Internet as hub)
“In-house” computing a thing of the past

33. Web Services Standards
Three software standards
XML: describe data in a standard way
WSDL: web services make themselves known by publishing their description in an XML document.
UDDI: descriptions are stores in UDDI register / “yellow pages” of web services
Three communication standards
SOAP: Web services communicate using SOAP
HTTP: Web sites have addresses that use HTTP
TCP/IP: Transmit messages across networks

34. Significance of Web Services
How does it impact business and work?
From proprietary IT architecture to Web Services based on openness of Internet
Faster market response
High variety of possibilities
Pay only for needed functionality

35. General Motors Case Example: Web Services
Build-to-stock  Build-to-order
Locate-to-order Web service
Dealers can use to easily find a specific car a customer might want in the inventory
Order-to-delivery
shortens the time to deliver a custom-ordered vehicle
Rewards?
Cut $25 billion inventory by 50%
Potentially shave off $1,000 off the cost of each vehicle

36. Service-Oriented Architecture
SOA a form of distributed computing
Similar architecture concept to Web Services
Can be implemented with Web Services
Thinks about how to expose the data and functions in a way that other systems can easily use rather than think about how to get information out of one system and into the other
One service would open a new account, another would update a customer account, a third would close an account

37. Credit Suisse Case Example: Service Oriented Architecture
Proprietary middleware  SOA
Implemented two “information buses”
Service Bus
Integrates front-end and back-end applications based on demand-pull model
Event Bus
Integrates back-end systems, ensuring all systems (host applications, ERP systems, databases, etc) are using the same up-to-date data