Data hierarchy (Figure 6.1)
bit - smallest piece of data
byte – character
field - group of bytes
record - related fields
file - related records
database - related files and data about them
File Processing vs Database
•
•
•
•
Data independence
Data redundancy
Data consistency
Data sharing
Database Management Systems
• A software that organizes data for easy
retrieval and access
3 components (relational):
• Data definition language (tables)
• Data manipulation language (SQL)
• Data dictionary (fields, field types, keys …)
Telecommunications
• Communications by electronic means over some distance
• Telecommunication systems functions
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–
–
–
–
–
–
transmits information
establishes a path/connection between the sender and receiver
directs messages along the most efficient paths
ensures messages reaching the right receiver
edits data by performing error checking and reformatting
converts messages from one device to another
controls information flow
Figure 7.5 Five Components of a Telecommunication System
• Computer (process information)
• Software (network, access, transmission, error, and security control)
• Processor (modems, mulitplexer, …)
• Channel (fiber-optic, cable, satellite, …)
• Input/Output Devices (send/receive data)
Figure 7.2 MOdulation/DEModulation
Networks
• Ways of organizing telecommunications components:
– Topology
• Star
• Bus
• Ring
– Scope
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•
•
•
•
Private branch exchange (PBX), e.g., UK’s phone systems
Local area networks (LAN), e.g., BEIC lab
Wide area networks (WAN), e.g., UK’s web
Value-added networks (VAN), e.g., AOL
The Internet
Figure 7.8 A Local Area Network (LAN)
History of the Internet
• ARPANET (1969-1990)
– the U.S. Defense Department’s Advanced Research
Projects Agency (ARPA) to facilitate data sharing
• NSFNET (1986-1995)
– the National Science Foundation’s (NSF) national
network for university communications
• Internet (1990)
– Business use of the Internet promotes the
development of World Wide Web
World Wide Web
• A system and a set of standards for storing,
retrieving, formatting, and displaying
information in a networked environment
using graphical user interfaces and dynamic
links to documents
Web Terms
• HTML (Hypertext Markup Language) is a
standard language for Web site programming so
that navigation tools are able to display the Web
site as it was designed without the need to
coordinate software packages. Simple html can be
created directly through word processing and
presentation packages. Special Web authoring
tools exist to create more elaborate pages.
Web Terms
• Uniform Resource Locator is the address
of a specific resource on the Internet
• A Web browser is a tool for navigation and
display of sites. There are many Web
browsers with Mosaic being the first.
• Search engines help users locate
information on specific topics
• Standards
– Transmission Control Protocol/Internet
Protocol (TCP/IP), DOE, 1972:
• Layered protocol (Link, Network, Transport,
Application) that sends data as packets
– Integrated Services Digital Network (ISDN)
• Standards for transmitting voice data, and video
over phone lines
Applications
• E-mail, voice mail, fax
• Teleconferencing, videoconferencing
• Electronic data interchange: direct electronic
exchange of business transaction documents between two
separate organizations
• Electronic commerce