Transcript DIS Revision

DIS Revision
Week 13
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What are Distributed
Information Systems?
 “Systems
where the processing
and/or data storage are distributed
across two or more autonomous
networked computers”
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Almost all information systems in current use are,
by this definition, distributed
 The most common experience for most people of a
distributed system is from the use of the web.
DIS are complex
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1000s of component
 100s of supplier
 Sheer size in database and users
 Geographic spread
 Frequent change
We are approaching DIS as
an architect would
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Carry out the broad design
 Architects use structural and mechanical
engineers and the various trades
 System architects use use network
specialists, programmers, analysts, DBAs
and the like
 But are responsible overall
 So we need to know enough to specify and
supervise
What are standards &
protocols?

These terms are used fairly interchangeably in the
computer world. It can be argued that a protocol is
a type of standard peculiar to computer systems,
usually with a time element.
 A protocol
defines the format and
order of messages exchanged
between two communicating entities,
and the actions taken on receipt or
transmission of a message.
Some examples of standards
& Protocols
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De facto (by fact – by general acceptance)
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De jure (by law – set by an officially recognised
body)
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TCP/IP – managed by the Internet Engineering Task Force
(IETF)
HTTP, HTML & XML managed by the IEFT & W3
Consortium
IBM PC platform – established by IBM, Intel & Microsoft
LAN standards – 802.x set by IEEE
V series (V.32, V.33) X series (X.25, X.500) ISDN set by
ITU.T used to be called CCITT set up by the United Nations
But the boundaries are blurred
Business rules
 They
are the rules, definitions and
policies that are necessary for any
organisation to function
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Examples are:
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Course pre-requisites – INFO2000 or INFO2006 for this course
Parking fines must be paid within 30 days
Employees who work less than 30 hours per week are judged as
part-time etc
Many are very complex
 The DIS automates many of those rules
 But often not precisely defined until then
 And very difficult to do – but necessary!
There are many different
types of applications in a DIS

Communications
 Information
 Commercial
 Education, Health etc
 Government
 Multi-media
 E-Commerce
Structural change has been
underway in business for some years
Integration of the world’s capital markets
 Reduction in trade and capital barriers
 Privatisation of government services
 Business Process Re-engineering (BPR)
 Enterprise Resource Planning systems (ERP)
 Technology fitting Moore’s Law
 Focus on core business & outsourcing
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Characteristics of the
traditional model
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High fixed capital
 Owned production capacity
 Sell what you make
 Reduce cost of production by
– Large scale plant
– Increased throughput
Characteristics of the new model

Very few capital assets
 Often no production capacity
 Concentrates on customers (CRM) and
brand
 Speed of response is the driver
 Manages a network of suppliers
 Suppliers bid via an electronic market
 Design is collaborative – via internet
Characteristics of the new
model (cont.)
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Customer orders placed via Internet
Orders are routed automatically to the appropriate
suppliers and component manufacturers
Goods are routed directly from supplier to
customer
Customers and suppliers have full access to
computer systems showing status of orders
Administration systems are also outsourced
Corporate Business Strategies

Increasingly, businesses have 3-5 year
business strategies. These seek to define the
business they are in and their plans for the
next 3-5 years
 IT is an enabler and a critical success factor
is achieving those plans
 Thus a corporate IT strategy is an
underlying requirement
We start with a Business
Strategy
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In most cases an organisation will start with a
business strategy. This is increasingly necessary
because:
– Business conditions change rapidly
– Competition is actively encouraged
– Management teams change more frequently
– Business is more complex
– Organisations have to be focused
– Organisations seek to re-invent themselves rapidly
Many objectives will affect IT
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Some of these will directly require IT services
IT can also feed into the process and facilitate new
strategies and objectives
IT must brief Senior management on emerging
technologies
Differentiate between technologies that are there and
those which maybe offer more potential but not yet
certain
IT may also prevent strategies from being followed
It is an Iterative process
Where do we start in the
design process?
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Like a building architect, by assembling a
brief
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The Corporate IT strategy defines many of the
components
The problem definition set the functional boundaries
Existing systems pose some constraints
Volumes of data, transactions and users establish the
size
The location of users sets parameters on security,
internationalisation and controls
User community agrees performance criteria
Design is an iterative process
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It starts in the feasibility study.
 Often a number of preliminary designs are
looked at this stage, costed and discussed
 As the stages of development proceed, so
the design is reworked and refined
 Often the final design bears little similarity
to the one opted for in the feasibility study
The feasibility study will
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Define the key processes
Define the initial data model
Specify interface requirements to other systems
Identify and review the relevant corporate IT
strategies and standards
Collect the volumes
Review solutions to the same problem in other
organisations
Identify and review possible application packages
As the process continues
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Make or buy decisions will be made
Development tools and methodologies will be put
in place
DBMS will be selected
Development and implementation plans will be
developed
Capital and operating costs will be estimated
Configuration and location of servers and data
storage will be determined
Networks will be designed, upgraded and sized
And continues
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Risks will be identified and minimisation
strategies developed
Performance criteria agreed
Security requirements established
Implementation steps identified
The client server model selected
Infrastructure components identified in detail
The data model is developed
Processes are analysed and designed
The main clients server models
Centralised
Presentation
PC
LAN
Client server
2 Tier
3 Tier
Presentation
Presentation
Presentation
Presentation
Presentation
Presentation
Application
Application
4 Tier
Presentation
Database
Network – LAN and WAN
Presentation
Presentation
Application
Application
Application
Database
File system
File system
Database
Database
Database
File system
File system
File system
Database tier
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This is the most easily defined
 It parses and executes SQL to:
– Update the database, or
– Make the query and pass back the requested
data set
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Maintains transaction integrity (ACID) for a
single database – moves back to application
tier for multiple databases
Application tier
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Executes the code that process the application
 Sometime the interface between Presentation and
Application is blurred
 Varies between implementation
 An example might help: In an enrolment system;
– Presentation tier would
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gather the details of the course and
establish that they were valid.
– Application tier would
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Process the rules to ensure you were eligible to take those
courses,
update your records via SQL to the Database tier, and
draft a course schedule for the Presentation layer to show you.
3&4 Tier Presentation
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In a three tier, the Presentation layer code is held
remotely on the client or a local server. It presents
forms etc for viewing or for data entry. It still has
application specific material that must be updated
if an application changes
 Four tier usually means a WEB based system
 The presentation layer is then split – the
application specific stuff stays in the web server so
that the only part that is required to be resident in
the client is the Browser
As DIS architects, we want a
network service that:
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Provides a reliable message transport
 Gives acceptable & predictable
transmission times
 Allows a host at any location to be part of
the system
 Does not require our application to adapt to
any specific network characteristics.
Voice Networks
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Voice networks were:
– Circuit switched
– Analogue
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Circuit switching requires all resources to be
dedicated for the length of the connection
 Voice is a reasonably consistent user of bandwidth
for the length of the connection
 Data on analogue circuits requires a modem
Data Networks
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Data does not use switched circuits efficiently as
data is bursty – large quantities of data in bursts
followed by quite periods
Packet switched gives better utilisation as many
users can then share the channels
Digital signals allow greater bandwidth
High capacity lines can be multiplexed into
multiple digital channels
Voice can be digitised and packetised for
transmission on data networks – eventually all
networks will be packet switched
Packet switched networks
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Messages are broken into packets usually variable
in length but not of unlimited length
Packet of data is wrapped in an enveloped with an
electronic address
Packets sent down the line like cars on a highway
Routers act like road junctions, directing the
packet along the right road to get to the eventual
destination
Packet switched networks can be virtual circuit or
datagram
Effective end-to-end transfer
rates determined by:
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The bandwidth of each link
 The Latency at each switch
– The Store & Forward process
– The congestion or queuing at switches
– Lost packets due to buffer overflow
– Error detection and correction mechanism
The Layers of the Internet
architecture
Application – HTTP, FTP etc
 Transport – TCP and UDP
 Network – IP – connectionless & unreliable
 Data Link – FR, ATM
 Physical
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Domain Name Service
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Converts host names e.g. cs.usyd.edu.au to
32 bit IP addresses 192.154.32.9
 IP addresses made up of two parts
– Network address
– Host or device address
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IPv6 will introduce 128 bit addresses
(maybe)
An Organisation’s network can
be:
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Leased channels
 VPN Virtual Private Network
 VPN on Public network
 Public Network
 Combination of some or all or these
Leased circuits
High initial fixed cost – may be cheaper if
bandwidth well utilised
 Fixed bandwidth – not easy to add
bandwidth
 Longer time frame to set-up
 Circuits may not be readily available
 Not flexible for mobile users
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Frame Relay VPNs
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Easier to set-up
Buy as much bandwidth (CIR) as needed and
increase with a phone call
FR allow bursting above CIR if capacity available.
FR may not be available in some remote locations
Thus POP may not be available for local call
access from mobile users
Network can be managed by supplier
VPNs on Internet
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Cheap to set up
 Variable bandwidth
 Wide availability is good for remote offices
and mobile users
 No guaranteed bandwidth although QoS is
coming
 Some concern about data security
Hubs, (Bridges) Switches & Routers
Application
Application
Transport
Transport
Network
Link
Physical
Host
Physical
Hub
Network
Network
Link
Link
Link
Physical
Physical
Physical
Router
Host
Bridge or
Switch
Hubs
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Physical level devices
 They work at the bit level
 When a bit is received from one line, it propagates
down all the other lines
 Can carry out limited network management
functions – if an adaptor is faulty and floods the
line with bits, the hub can internally disconnect
that line
 Extends the length of the LAN, because segment
UTP lengths have discrete limits.
Bridges
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Are Data link layer devices
 Work on frames and use adaptor addresses
 Store & forward devices
 They act as a switch and only send frames down the line where
the destination device is, thus if the frame address is not
“over” the bridge the frame is not passed on.
 Create limited area “collision zones”
 Usually support 2-4 links
 Can connect links of different bandwidths eg 10 & 100mbps
Ethernet
 They are plug & play devices – they learn where adaptors are
 Will disable duplicate paths in its internal tables.
Switches
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Are newer Link layer Ethernet devices (but there
are WAN switches as well e.g. ATM switches)
 Tend to replace bridges but do similar things
 Larger number of links 12+
 Higher performance design – required because of
larger number of links
 Facilitates connection of servers
Routers
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Network layers devices
 Transfer IP packets and use IP addresses
 Transfer packets down the best link to get to the
destination host
 Support redundant links
 While they are inherently slower than hubs and
switches, the more sophisticated technologies used
compensate for that.
 They are the “end device” of separate networks
within the Internet
 Can be used as simple firewalls by filtering out
unwanted packets.
Routing algorithms
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The network layer has to determine the route the
message is to take
 In a virtual circuit all packets for the connection
will follow the same path
 In a datagram service like IP, packets may take
different routes
 In both situations the routing algorithm within the
Network layer will determine the routes
Quality of Service
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One drawback with the Internet is that it is
democratic, and all packets are treated as
important as any other.
It provides “best effort” service
IPv4 has no mechanism to provide priority
This is needed for time critical applications such
as telephony, real time conferencing and high
performance transaction processing
QoS aims for a predictable and specifiable
bandwidth and latency
QoS the key to one network
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When packet switched networks can offer
the QoS of switched circuits, that will be the
day when all major users stop having two
networks
 Service providers are aware of this
 The network must be able to differentiate
between delay sensitive and delay
insensitive applications
QoS requires:
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The ability to request and receive resource
reservation
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Bandwidth
Router buffers
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Prioritisation where network traffic is classified
and priority given according to bandwidth
management policy
 These services could be for:
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An individual data stream
Aggregate flows of a particular type
The Web is an application!
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To many people The Internet and The Web are
synonymous
 But we know that The Web is an application that
sits at the application level of the Internet
 But is is the biggest, and therefore the most
important to most people
 But theoretically it could use different protocols
on a different network
Some definitions
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HTML HyperText Mark-up Language describes
how the document is to be presented with tags or
meta-data imbedded in the document. The
Browser then uses that meta-data to format the
document
 HTTP is the application level protocol or service,
for establishing connections and transmitting
messages, between the Browser client and the Web
server
Statelessness in HTTP
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HTTP is a stateless protocol
 When a resource has been sent, the server
keeps no record of the exchange, so that if a
second request is made by the same client, it
is as if this was first contact with that client
 This is not satisfactory for many complex
transactions, say completing a multi-page
form
Techniques for improving Web
performance
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Caching
 Load balancing
 Content Distribution Networks
Caching
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Initially implemented near the client in a proxy
server operated by the organisation – all requests
are first directed at the proxy server. If it cannot
supply then the request is passed on to the target
server.
 Works on the basis that similar users frequently
access the same pages – between 20-70% of
requests can be satisfied this way, reducing
bandwidth on the WAN
Caching Cont.
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Dynamically created pages cannot be
cached
 The risk of out-of-date information is
reduced by time stamping the page with an
expiry time when it must be refreshed
 Caching also provided close to the original
site to take load off main server
Caching Services
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Caching now provided by service providers that
maintain an array of cache servers
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Akamii has 2000 servers in 40 countries. The site owners
decide which pages to be cached
NLANR is another with a hierachy of backbone and regional
caches
One cache can obtain an object from another
cache using ICP (Internet Caching Protocol)
 Large ISPs serving low bandwidth clients provide
this service
 Caches are being developed to handle streaming
video and audio – eventually supplying on
demand music, TV and movies over the Internet
Load Balancing
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This enables groups of servers to service incoming
requests
Data is replicated to the servers
The request is sent to the server with the lowest
load
Cookies can be used to identify high priority
clients and route their request accordingly
We saw earlier how DNS can be used to provide
simple load balancing
Content Distribution Networks
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This takes load balancing one stage further
by distributing the servers geographically
closer to the users.
 This
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Reduces network hops
Increases overall resilience
Increases scalability
End of Thursday revision
Integration facilities are
necessary to link:
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components (or objects) within an application
distributed over multiple hosts
 diverse applications within an organisation
 applications across organisational boundaries
Because application developers
do not have any agreed protocol
Two main integration
approaches
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Passing data between two quite different
systems
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Data incompatibilities – content & structure
Timing incompatibilities
Component linking between components in
the one system, or between components in
compatible systems
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Finding the component
Defining a common interface
Data incompatibilities in
Integration of disparate systems
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Primary keys in disparate systems are invariably
different
Common attributes have different names and field
lengths
Classifications appear the same but are different
Classification codes or names are different
Sometime differences are for good reason
Some parts of an organisation need more attributes
than others
Timing incompatibilities
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Timing of the generation and acceptance of
the data
 Back-up and recovery differences result in
risk of data loss or duplication
 Progressive implementation programmes,
the frequency of new releases etc all make
interface change frequent and difficult to
manage
Enterprise Application Integration
 EAI originated in the MOM market
 The connector is often provided by the application supplier but
may have to be coded for legacy systems
 The EAI provides
 translation,
 rules engine that can process or trigger an event
 transport mechanism – usually IBM’s MQ Series,
 and is usually asynchronous
 transaction queue
A simple example of our case study
Global
Theatre
Data
warehouse
EAI Hub
v
HR
Country
Client
Accounting
EAI is fast developing
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Richer application servers (hub)
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Facilities for interface definition
Business rules for converting data
Fail over protection
Database access
Different transport models
Use of XML as a data definition standard
 Closer to real time integration with publish
and subscribe model
Component linking
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Applications spread over multiple hosts
Components written in multiple languages
Components developed when the hardware &
operating system is not known
Components developed by many independent persons
or organisations
The Location of components is not known
Load balancing and fail over with multiple servers of
the one type
Databases of different types need to be updated by the
one transaction.
Components are spread
over all of these hosts.
Clients
Internet
LAN
Web server
Transaction
servers
Database server(s)
Some characteristics of
component linking
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Applications must access a registry at run-time to
find out where components are located
 There must be a uniform scheme for passing
information between components and for
accessing data from multiple heterogeneous
sources
 Components must be designed to interact with
middleware and then it can locate resources and
communicate with them
 Middleware can present the illusion of a single
underlying server
Approaches to component
linking
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In WEB based systems, HTTP is the main link
between the client and the WEB server
 The usual interface between the database server
and the other hosts is SQL, usually with a DBMS
supplier provided transport mechanism
 This leaves the interface between the Web server
and the transaction servers, and in three tier
between the client and the transaction servers
The basic approaches
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Remote Procedure Call (RPC) middleware
 Message Oriented Middleware (MOM)
 Transaction Processing middleware
 Distributed Object/component middleware
(DOM)
What is XML ?
XML is a simplified markup language to facilitate the
exchange of information: providing both format and
content
• A group of standards (XML, XSL,
XML Schema, XLL, etc)
ebXML
VoXML
xCBL
RosettaNet
etc.
• Is different to HTML which is a
presentation language which
provides no semantic information.
98’ XML
89’ HTML
86’ SGML
Generalized
Markup
Language
60’s
80’s
90’s
Today
Promise of XML
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XML is expected to:
• Revolutionise electronic publishing by allowing for a
better indexing of data and the separation of content
information from display information
• Improve business communication by facilitating the
definition and sharing of common XML formats or
vocabularies as well as the transformation of differing
XML formats
• Help facilitate the adoption of e-Commerce and as
content will be displayed not only on desktop web
browsers, but also PDAs, cellular telephones, and
whatever other devices the future may bring us
Bringing the Pieces Together
- Presentation
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A typical presentation scenario:
1. The XML document and an XSLT sheet is read by an XSLT engine.
2. The XSLT engine creates output as an XSL-FO document or some
display format such as HTML.
3. HTML documents are sent to a browser.
4. XSL-FO may be processed into other document types such as PDF.
Traditional Responses
Across Organisations
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Interfaces
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EDI or Custom “standard” (e.g. integrion, SWIFT)
Reinventing “interchange data structures”
Validation of data passed built into each “receiving” application
Data structure changes require massive rebuild & retest
Problems with today’s approach
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Difficulties to get people to agree
Difficult to get participants to agree on technical platforms and
associated costs (e.g. MQ Series, other EAI tools, etc)
Standards (e.g. EDIFACT) are inadequate for industry solutions
so require customisation
Administration of change across organisations
Solutions
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XML Response to the
Problem
Low cost mechanism which is easy to agree on
Industry bodies to define industry schema (Accord, FiXML,CML, etc)
Interchange data semantics & validation rules ubiquitously available
Data can be validated by the schema before information is accepted,
Ready availability of skills in the marketplace
XML parsers & other tools available in most languages and on most
platforms
Ease of data transformation to adapt to needs of sending/receiving
application data structures
Reduced need for “big bang” synchronisation of change associated with
new data structures
Challenges
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Performance concerns (verbose)
Many XML standards (DirXML, UDDI, etc)
Relatively young toolset
Components and Communication
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What is a component?
– A “component” encapsulates business logic (e.g., a sales order,
customer information), which is packaged and distributed around the
network.
– Large-grained objects, not necessarily using object technology
– Component technology provides packaging, distribution, and
language interoperability.
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What is component-oriented middleware?
– The set of technical components that allow business logic to be
encapsulated in the middle tier of a 3-tier application architecture.
– Provides framework for security, location hiding, scalability, state and
transaction management
Typical Architecture
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Model – View – Controller Construct
– Supports multiple presentation layers
Presentation
– Increases flexibility and adaptability
– Enforces architecture and application
uniformity
Application
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Technical Infrastructure
– Enforces common rules and simplifies
Database
Technical
Infrastructure
programming interfaces
– provides platform and service location
transparency
– provides adaptability and flexibility
– Focuses developers on business logic,
not technical details
The right architecture can solve…
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Performance and Scalability
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Persistence / Transaction
Management
• COM+
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State Management
• EJB
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Interoperability
• CORBA
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Security
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Naming Services
Key characteristics: COM+
and .NET
HTTP
HTML
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Language Independent
–
Presentation Tier
ASP.NET
SOAP/XML
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Application Tier
COM+
Windows 2000, IIS,
.Net Framework,
.Net Enterprise Servers
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VB Script and Active/X
Control/event model
COM+
–
–
–
–
ADO.NET
Database Tier
SQL Server/Oracle/DB2
Interface Development
–
–
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Common Language Runtime
Object Pooling & Security Services
Transaction Management: MTS
Queuing: MSMQ
Naming Services: ActiveDirectory
Platforms Supported
–
–
Windows OS
ODBC Compliant Database
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XML Across Tiers
 Web Services
–
–
Application Servers
Collaboration Services
Key characteristics: EJB /
J2EE
HTTP
HTML
Presentation Tier
Java Servlets & Server Pages
RMI/IIOP
Application Tier
Enterprise Java Beans
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– Java Virtual Machine
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Windows 2000/Unix,
J2EE Platform,
OO Development
Platform/OS Independent
– JDBC compliant database
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EJB
–
–
–
–
–
JDBC
Database Tier
JDBC compatible DB
Single Language: Java
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Object Pooling & Security Services
Transaction Management: JTA
Naming Services: JNDI
Queuing: JMS
State Management: Entity Bean
Vendor Products
– Add Application Servers
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Web Services
– Sun’s ONE Framework
International Issues
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Dates
Calendar
Field sizes
Currency & Currency conversion
Character sets & sorting sequences
Language
Cultural & commercial
Legal issues – taxes, privacy etc
There are two general
measures of performance
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The time an individual takes to complete a
task – RESPONSE TIME
 The number of transactions the system can
process in a given time period THROUGHPUT
But won’t one vary directly
with the other?
Concurrency is the answer
Throughput and scalability

As resources are added, more disk, more
memory, faster processors, more bandwidth,
then the system should increase throughput
proportionally
 But it depends on the architecture of the
system as to whether it can use the
resources at all, and whether you get a
proportional increase
All areas of the system affect
performance
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User Interface Design
System design
Programming
System architecture
Database implementation
Operating system, Middleware and Server
hardware
Network
Platform evaluation

The platform consists of:
– Operating systems
– Middleware (MOM, TP Monitors, Distributed
Component services)
– Server computers

Usually best evaluated as a unit
 Sometimes all or some of the suppliers of these
elements are organisation standards
 But the precise platform still needs to be specified
and evaluated for suitability for the application
Benchmarks are not easy

At the time the benchmark needs to be
done, the application code is usually not
written. So we can’t benchmark the actual
application.
 Setting up quantities of benchmark data,
meeting the structure of the new database is
a difficult and time consuming task
 An alternative is to use TPC benchmarks
What are TPC benchmarks?
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The Transaction Processing Council is an
independent organisation that prepares and audits
benchmarks of combinations of Operating system,
DBMS and Server and publishes those
benchmarks in a comparative form.
It has been functioning for 10+ years
It specifies a number of benchmarks, related as far
as possible to real world situation
It monitors and audits tests by manufacturers to
ensure all conditions are met and the results are
comparative
Website is www.tpc.org
TPC-C
TPC-C simulates an order entry environment
 Involves a mix of five transaction types of different
complexity
 Multiple on-line terminal sessions
 Moderate system and application execution time
 Significant disk input/output
 Transaction integrity (ACID properties)
 Non-uniform distribution of data access through
primary and secondary keys
 Databases consisting of many tables with a wide
variety of sizes, attributes, and relationships
 Contention on data access and update

What do we mean by reliability?
Correct – do what the system say it will do
correctly
 Available – Be available within the agreed
time frame
 Consistent – do it the same way with much
the same response time on each occasion

RAID

Redundant Arrays of Independent Disks
 Groups of drives are linked to a special
controller
 They appear as a single logical drive
 Take advantage of multiple physical drive to
store data redundantly
 Six different RAID approaches numbered 0
to 5
0
Data striping, block oriented
No redundancy – no protection from disk loss
Reads and writes for contiguous block overlap, giving improved
performance
No space overhead

1
Disk mirroring – all data written to two identical drives
Full data protection
If one fails the system can continue using the other
Improved read access
Doubles disk space required
Easy to implement, easy to recover

5
Data striping, block oriented, distributed parity
Full error protection, but slower to recover than 1
Slow write due to parity computation,
Good read performance, same as for Raid 0 but not as good as 1
25% overhead in disk space
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Why do we need security?

Authenticate people wanting to use the system
 Prevent unauthorised persons from
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Prevent authorised persons from
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accessing the system
Stealing information
Doing malicious damage
Doing things they ought not
Seeing data they ought not
Identifying unauthorised access
Security risks are within

Most books concentrate on network security, but
most DIS are of little interest to people outside
 Most security breaches are from within the
organisation and by relatively technically illiterate
people
 They are by people who want something they
ought not have – like your medical records, your
pay details, your exam marks – perhaps next
month’s DIS exam!
Security starts with policies

Hardware and software implement policies
 The police and the law courts would be of little
use without legislation
 The policy statement will:
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State that security is important to the organisation
Define the principles of the policy
Define what constitutes acceptable use
Give notice that security is monitored
State what the procedure is when security is breached
Risk areas where security
need to be enforced

Authenticating the person wanting access to
the system
 Limiting the activities the person can do
 Limiting the data the person can see
 Restricting access to the corporate network
from outside
 Ensuring communications are secure
Authenticating the user
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The whole mechanism is dependent on a reliable
identification of the person accessing the system
In most systems this is done by password
But passwords can be easily misused
KPMG auditor quoted as saying most passwords
can be broken within 30 seconds
Canadian police reckon the key to a person’s
password is within 2 metres of his or her PC
But we are asked to remember so many password
and then change them every three months
There are other means of
identification

Keyboards can accept swiped ID cards
 Tokens that generate random numbers in
synch with the operating system
 Modems generate password or require call
back
 Physical access via electronic key
 Thumb, voice or retina scan
Limiting activities

The user is assigned to a group or class
based on grade, position or responsibility
 The group has rights to do certain things
 The application restricts access to menus
and buttons that initiate functions based on
that class
Limiting the data the user can
see or change

Can be in the application based on class, or
attributes like ID, grade and department

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The application can preset parameters on list and enquiry
functions
Can use database functionality
– ACLs restrict
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Access to read or write
Limit access to specific tables
Limit access to views of tables (or joins)
Restrict access to DBA functions
Firewalls protect the internal
network

Routers act as packet filters
 Application level firewalls
Application
Internal
Network
Outside world
Router
Firewalls
Ensuring communications are
secure
Secrecy – only the two parties (person or
process) should understand the messages
 Authentication – each party should know
the messages are from the right person
 Message integrity – the messages must not
be able to be changed
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