Distributed Systems

• Virtually all large computer-based systems are now distributed systems.
• Information processing is distributted over several computers rather confined to a single machine.
• Distributed SWE is therefore very important for enterprise computing systems
  • Enterprise is when a business is about more than one thing
  • usually multiple businesses
• one of the largest problems with this is security.

System Types: SUPER IMPORTANT

• Personal Systems that are not distrubted and that are designed to run on a personal computer or workstation.
• Embedded Systems: that run on a single processor or on an integrated grou of processors.
• Distributed Systems: Where the system software runs on a loosely integrated gorup of cooperating processors linked by a network.

Distributed System Characteristics

• Resource Sharing
  • Sharing of hardware and software resources
• Openness
  • Use of equipment and software from different vendors.
• Concurrency
  • Conccurent processing to enhance performance.
• Scalability
  • Increased throughput by adding new resources.
• Fault tolerance
  • The ability to coninue in operation after a fualt has occured.

Distributed system disadvantages

• Compelexity
  • Typically, distributed systems are more complex than centralised systems.
• Security
  • More susceptible to external attack.
• Manageability
  • More effort required for system management.
• Unpredictability
  • Unpredictable response depending on the system organization and network load

Distributed systems architectures

2 Types

• Client-server Architectures
  • Distributed services which are called on by clients. Servers that provide services are treated differently from clients that use services.
• Distributed object architectures
  • No distinction between clients and servers. Any object on the system may provide and use services from other objects

MiddleWare (IMPORTANT)

• Software that manges and supports the different components of distributed systems .
• Middleware is usually off the shelf rather than specfically written software. e.g.
  • Transcations, processing monitors;
  • data converters;
  • Communication controllers.

Big vs Little Endien

Intel, microsoft... :

• Use little endien

Apple, Amazon etc... :

• Use Big endien

Little endien:

• Pushes small to big
• DATA: 456
  • Little endien: 654
  • Box

Big Endien:

• Pusshes big to small
• DATA: 456
  • Big Endien 456
  • Triangle

Thats where middleware comes in:

• Can convert little to big, Big to little
• box to triangle, triangle to box

CORBA is another middleware Converter

CLient Server Architecture

• The application is modelled as a set of services that are provided by servers and a set of clients that use these services
• Clients know of servers but servers need not know of clients
• client and servers are logical processes
• The mapping of processors to processess is not necessarily 1 : 1

Servers are Squares, clients are circles

looks a lot like a bunch of nodes and clusters

Layered application architecture

• Presentation Layer
  • Concerned with presenting the results of a computation to system users and collecting user inputs.
• Application processing layer
  • Concerned with providing application specific functionality e.g. in a banking system, banking functions such as a open accounts, close acc. etc.
• Data management layer
  • concerned with managing the system database

Thin and Fat Clients 2 models

Thin client model:

• all of application processing and data mangement is carried out on the Server

Fat client model:

• Server is only responsable for data management, the software on the client implements the application logic

Who uses fat client:

• Microsoft (how many copys of word do you have)
• Intel
• Dell

Who uses Thin client:

• Google
• Amazon
• Nvidia

Everybody is moving to thin client, because thin is better

Distributed Object Architectures

• No distinction in a distribured object architectures between clients and servers
• each distributable entity is an object that provides services to other objects adn recieves services from objects
• Object communication is through a middleware system called an object request broker (ORB)
• Distributed object architectures are more complex to design than C/S systems

a diagram of this is similar to class objects

Exam questions: who handles the communication is distributed object architecture?

• ORB: Object Request Broker

Advantages of Distributed object arch

• Allows the system designer to delay decisions
• very open
• allowed to use it as client server as well!

Uses of distributed object Arch

• As a logical model its good
• and a client server
• Can be used in data mining systems
  • Data mining (comparing data with each other)
  • Integrators use deep learning to learn off the data
  • Kinda like how beer and baby products are next to each other

CORBA (common object request broker architecture)

• Middleware for distributed computing 2 level
  • At the lgocial communication, allows object on diff computers to exchange data
  • At the component level provides a basis for delvoping compatable components

Exam questions:

What does corba stand for?

• CORBA (common object request broker architecture)

What is Corba Application structure (list or draw it)

• Application objects (Your own version of stuff / flavor / subroutines-api's)
• Domain Facilities (Display of information)
• Object Request Broker (Gathering information)
• CORBA Services (runs and manages all the services)
• Horizontal CORBA facilities (Common services for each corba task / Fonts and colors)

Corba is the heart of Distributed object architectures

Application Structure

• Application object
• This is defined by OMG

Corba objects

• CORBA objects are comparable in principle to objects in C++ & java
• Corba objects must have a seperate interface definition that is expressed using a common language (IDL) similar to C++
• Interface Definition Languages (IDL)
• There is a mapping form IDL to programming languages
• Therefore objects wirtten in diffent languages can communicate with each other

Peer-to-peer architecture

• Peer to peer (p2p) Systems are decentrailised systems where computations may be carried out by any node in the network
• The overall system is designed to take advantage of the computation power and storage of a large networked computers
• Most p2p systems have been personal system but there is increaing business use of this technology.

p2p communication is a lot like a game of telephone but the data is not lost!

p2p architectural models

• The logical network arch.
  • Decentralised arch. ( each node just holds info and p2p has to repeat its process again)
  • semi-centralised arch. (semi-centralized has a discovery server where it saves some info that has been searched for before and shortens the search time)
• Application arch.
  • the generacic org of componets
• focus is on network architecutre

Generic Service

• An act/performance offered by one party to another.
• Service probvison is therefore independent of the application using the service

WEB SERVICES DIAGRAM (important for exam)

• Service registry
• Service requestor
• Service Provider

Services and distrbuted objects

• Provider independence
• public advertising
• pay for use

All of these are written in soap (which soap is written in XML)

service standards

• Services are based on agreed, XML-based standards, so they can provide on any platform in any lang.
• Key standards
  • SOAP - Simple Object Access Protocol (message in an envolope
  • WSDL - WEb Services Description Language
  • UDDI - Universal Decription, Discovery and Integration

Exam question:

Draw xml diagram

what technologies included

what are they based on