CS 501: Software EngineeringFall 2000

Lecture 14

System Architecture IData Intensive Systems

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Administration

Midterm examination, October 16, 7:30 to 8:30 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:

Data input Master fileTransaction Bill

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

Data input

Master file

Edit & validation

read only

errors

Validated transactions

Incoming transactions

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Batch Processing: Master File Update

Master fileupdate

Bills

Validated transactionsin batches

Sort by account

errors Reports

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

Data input Master fileTransactions Bills

read only

Customer service

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Example 2: A Small-town Stockbroker

• Transactions

Received by mail or over telephoneFor 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

Customer & account database

Products & services database

External services

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Real-time Transaction

Customer & account database

Products & services database

External services

Real-time transactions

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Real-time Transactions & Batch Processing

Customer & account database

Products & services database

External services

Real-time transactions

Batch processing

Data input

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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 commitreload from checkpoint + logdetailed 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

???

???

AA BB

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Merger of Two Banks: Architectural Options

I. Convert everything to System A.

convert databasesretrain staffenhance 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 connectionprivate, public, or virtual private networklocation of firewalls

• Protocolspoint-to-point, multicast, broadcastmessage passing, RPC, distributed objectsstateful or stateless

• Quality of service

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Network Choices

Public Internet:

Ubiquitous -- worldwideLow cost

Private network:

SecurityPredictable performanceChoice of protocols (e.g., IBM's SNA)

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Quality of Network Services

Performance

Maximum throughputVariations in throughputReal-time media (e.g., audio)

Business

SuppliersTrouble shooting and maintenanceUpgrades

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Firewall

Public network

Private 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 connectionan unknown packet type