1 cs 501 spring 2005 cs 501: software engineering lecture 13 system architecture and design i
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3 CS 501 Spring 2005
Quiz 2
Question 1
At the end of your CS 501 project, you mount your programs and documentation on GForge. The project team gives the client an unrestricted license to use the project for the client's purposes but not to distribute it to others.
A year later, the members of your team decide to go into business, selling a product that is based on your CS 501 system. You start a small company and hire three programmers.
4 CS 501 Spring 2005
Quiz 2
(a) You would like to keep the specification of the system secret. For this purpose you remove the system from GForge. Can you claim legal protection of the specification as trade secret?
No. The presumption is that by placing it on the GForge for a year, trade secret protection was lost, unless the GForge site is securely protected and, from the very start, everybody who saw the specification was required to keep it secret.
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Quiz 2
(b) Your company extends the system with a new component. Can you protect the specification of the new component as trade secret? If so, what procedure would you follow?
Yes, by creating procedures to keep the specification secret, e.g., by restricting access and my ensuring that everybody who has access understands the necessity of keeping it secret.
(c) Who owns the copyright in the original system? Who owns the copyright in your new component?
You own the copyright to the original system. To be more specific, the members of the project team jointly own the copyright.
The company owns the copyright to the new component.
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Quiz 2
(d) Can you charge the CS 501 client money to use your new component?
Yes. Unless your license says otherwise.
(e) Two of your programmers leave and start their own company. What use can they make of the programs that they wrote while working for your company? Can they write new software based on the specification of your new component?
They can make no use of the programs, without permission from the company. They were created as work for hire.
They cannot write software based on this specification. The specification is a trade secret of the company. The former employees cannot use it, but they can use ideas from it.
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System Architecture and Design
The overall design of a system:
• Computers and networks (e.g., monolithic, distributed)
• Interfaces and protocols (e.g., http, sql)
• Databases (e.g., relational, distributed)
• Security (e.g., smart card authentication)
• Operations (e.g., backup, archiving, audit trails)
• Software environments (e.g., languages, source control tools)
8 CS 501 Spring 2005
UML: System and Subsystem Modeling
Subsystem model
A grouping of elements that specifies what a part of a system should do.
Component (UML definition)
"A distributable piece of implementation of a system, including software code (source, binary, or executable) but also including business documents, etc., in a human system."
A component can be thought of as an implementation of a subsystem.
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UML Notation: Component & Node
orderform.java
A component is a physical and replaceable part of a system that conforms to and provides the realization of a set of interfaces.
Server
A node is a physical element that exists at run time and represents a computational resource.
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System Architecture Example:Extensibility in Web Browsers
Web browsers provide a flexible user interface through an extensible architecture.
Data types: helper applications, plug-ins
Protocols:HTTP, WAIS, Gopher, FTP, etc.proxies
Executable code:CGI scripts at serverJavaScript at clientJava applets
Style sheets:
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Web Interface: Basic
Web serverWeb browser
• Static pages from server
• All interaction requires communication with server
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UML Notation:Application Programming Interface (API)
API is an interface that is realized by one or more components.
WebServer
Get Post
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UML Notation: Interfaces
WebBrowser WebServer
HTTP
dependency
interface
realization
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Web User Interface: CGI Script
Web browser
• Scripts can configure pages
• Scripts can validate information
• All interaction requires communication with server
Data
CGIScripts
Web server
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UML Notation: CGI Interface Diagram
CGIScript
HTTP
Apache
CGI
SQL
MySQL
These components might be located on a single node.
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Web User Interface: JavaScript
Data
CGIScripts
Web server
Web browser
• JavaScripts can validate information as typed
• Some interactions are local
• Server interaction constrained by web protocols
JavaScript
html
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UML Notation: Package
A package is a general-purpose mechanism for organizing elements into groups.
Note: Some authors draw packages with a different shaped box:
JavaScript
JavaScript
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Example: Web Browser
HTTP
JavaScript
HTMLRenderEach package represents a group of objects.
WebBrowser
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Web User Interface: Applet
Any server
Web serversWeb browser
• Any executable code can run on client
• Client can connect to any server
Applets
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UML Diagrams and Specifications
For every subsystem, there is a choice of diagrams
Choose the diagrams that best model the system and are clearest to everybody.
In UML every diagram must have supporting specification
The diagrams shows the relationships among parts of the system, but much, much more detail is needed to specify a system explicitly.
For example, in the Applet Interface slide, at the very least, the specification should include the version of the protocols to be supported at the interfaces, the options (if any), and implementation restrictions.
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Components and Classes
Classes represent logical abstractions. They may be grouped into packages.
Components represent physical things. They may live on nodes.
Classes have attributes and operations directly. Components have operations that are reachable only through interfaces.
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Components and Replaceability
Components allow system to be assembled from binary replaceable elements.
• A component is physical -- bits not concepts
• A component can be replaced by any other component(s) that conforms to the interfaces.
• A component is part of a system.
• A component provides the realization of a set of interfaces.
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System Design: 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)
• E-commerce (e.g., Amazon.com)
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Batch ProcessingExample: Electricity Utility Billing
First attempt:
Data input Master fileTransaction Bill
Each transaction is handled as it arrives.
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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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Criticisms of First Attempt
Where is this first attempt weak?
• A bill is sent out for each transaction, even if there are several per day
• Bills are not sent out on a monthly cycle
• No way to answer customer queries
• No process for error checking and correction
• All activities are triggered by a transaction
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Batch Processing: Validation
Data input
Master file
Edit & validation
read only
errors
Batches of validated transactions
Batches of incoming transactions
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UML Deployment Diagram:Batch Processing Validation
MasterFile
EditCheck
ValidData
DataInput
RawData
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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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Interfaces to DataInput
DataInput
RawData
EditCheckErrorUpdateError
DataforCheck
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Benefits of Batch Updating
• All transactions for an account are processed together at appropriate intervals
• Backup and recovery have fixed checkpoints
• Better management control of operations
• Efficient use of staff and hardware
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Online Inquiry
Master file
read only
Customer Service
Customer Service department can read file, make annotations, and create transactions, but cannot change the master file.
New transaction
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Online Inquiry: Use Cases
CustomerServer
AnswerCustomer
NewTransaction
<<uses>>
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Data Intensive SystemsExample: 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)
• Links to external databases (e.g., stock markets, mutual funds, insurance companies)
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Real-time Transactions
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 to include in Specification
• Real-time service during scheduled hours with 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?
• How will staff dishonesty be controlled?
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Data Intensive Systems: 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.
This is an example of working with legacy systems.
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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