CS 501: Software Engineering Fall 2000

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CS 501 Software EngineeringFall 2000
Lecture 14 System Architecture I Data Intensive
Systems
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Administration
Midterm examination, October 16, 730 to 830
p.m. -- Hollister B14 (note change of room) --
See course notices for sample questions
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System Architecture
The overall design of a system Computers
and networks (e.g., monolithic, distributed)
Interfaces and protocols (e.g., http, CORBA)
Databases (e.g., relational, distributed)
Security (e.g., smart card authentication, SSL)
Operations (e.g., backup, archiving, audit
trails) Software environments (e.g.,
languages, source control tools)
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Data Intensive Systems
Examples Electricity utility customer
billing Telephone company call recording and
billing Car rental reservations (e.g.,
Hertz) Stock market brokerage (e.g., Charles
Schwab) Web sales (e.g., Amazon.com)
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Example 1 Electricity Utility Billing
First attempt
Bill
Master file
Transaction
Data input
Each transaction handled as it arrives.
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Criticisms of First Attempt
Where is this first attempt weak?
The requirements have not been specified!!!
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Transaction Types
Create account / close account Meter
reading Payment received Other credits
/ debits Check cleared / check bounced
Account query Correction of error etc.,
etc., etc.,
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Typical Requirements
All payments to be credited on day
received Customers must be able to query
account by telephone Cutting off service for
non-payment requires management
authorization Data input staff should
process n transactions per day per
person Error rate must be below 0.01
System available 99.9 of business hours
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Batch Processing Validation
errors
Edit validation
Incoming transactions
Validated transactions
Data input
read only
Master file
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Batch Processing Master File Update
Reports
errors
Validated transactions in batches
Sort by account
Bills
Master file update
Instructions
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Benefits of Batch Updating
All transactions for an account are
processed together Backup and recovery have
fixed checkpoints Better management control
of operations Efficient use of staff and
hardware
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Online Inquiry
Customer service
read only
Bills
Master file
Transactions
Data input
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Example 2 A Small-town Stockbroker
Transactions Received by mail or over
telephone For immediate or later action
Complex customer inquiries Highly
competitive market
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A Database Architecture
Database(s) Customer and account database
Financial products (e.g., account types,
pension plans, savings schemes) External
databases (e.g., stock markets, mutual funds,
insurance companies)
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Database Architecture
Products services database
External services
Customer account database
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Real-time Transaction
Real-time transactions
Products services database
External services
Customer account database
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Real-time Transactions Batch Processing
Data input
Real-time transactions
Batch processing
Products services database
External services
Customer account database
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Architectural considerations
Real-time service during scheduled hours
batch processing overnight Combine
information from several databases Database
consistency after any type of failure two-phase
commit reload from checkpoint log detailed
audit trail How will transaction errors be
avoided? How will transaction errors be
corrected?
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Example Merger of Two Banks
Each bank has a database with its customer
accounts. The databases are used by staff at
many branches and for back-office processing. The
requirement is to integrate the two banks so that
they appear to the customers to be a single
organization and to provide integrated service
from all branches.
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Merger of Two Banks Options
A
B
???
???
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Merger of Two Banks Architectural Options
I. Convert everything to System A. convert
databases retrain staff enhance System A
(software and hardware) discard System B II.
Build an interface between the databases in
System A and System B. III. Extend client
software so that it can interact with either
System A or System B database.
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Distributed Computing General Problem
An application that is running on one computer
wishes to use data or services provided by
another Network connection private,
public, or virtual private network location of
firewalls Protocols point-to-point,
multicast, broadcast message passing, RPC,
distributed objects stateful or stateless
Quality of service
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Network Choices
Public Internet Ubiquitous -- worldwide Low
cost Private network Security Predictable
performance Choice of protocols (e.g., IBM's
SNA)
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Quality of Network Services
Performance Maximum throughput Variations in
throughput Real-time media (e.g.,
audio) Business Suppliers Trouble shooting and
maintenance Upgrades
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Firewall
Private network
Public network
Firewall
A firewall is a computer at the junction of two
network segments that Inspects every packet
that attempts to cross the boundary Rejects
any packet that does not satisfy certain
criteria, e.g., an incoming request to open a
TCP connection an unknown packet type