Download Lecture #1: Course Overview

Short History of Data Storage
1725 - 1975: Punch Cards
Early data storage was very
inefficient
Processing of data was very
sequential
Data was stored as flat files
(read from beginning to end)
http://royal.pingdom.com/2008/04/08/the-history-of-computer-data-storage-in-pictures/
1932 - Disk Drum - 10kB
Formed central memory and secondary storage, also
primarily sequential, leading to flat files as best
performant data storage.
http://royal.pingdom.com/2008/04/08/the-history-of-computer-data-storage-in-pictures/
1951 - Magnetic Tape 7200 characters / second
Tape allowed much greater data
densities, but at slower access
times.
Blocks of data were written to the
tape with gaps where the tape is
accelerated/decelerated,
necessitating more advanced data
processing procedures.
http://royal.pingdom.com/2008/04/08/the-history-of-computer-data-storage-in-pictures/
1956 - Hard Disk - 5MB
Disks allowed for much closer to random access
memory than tapes.
This allowed the advent of data storage beyond flat
files.
http://royal.pingdom.com/2008/04/08/the-history-of-computer-data-storage-in-pictures/
1982 - Solid State Drive - 2MB
SSDs are basically Random Access Memory (RAM)
emulating Hard Disks and are optimized for storage
instead of access time.
http://www.storagesearch.com/chartingtheriseofssds.html /
Data + Base
1960 SAGE anti-aircraft
command and control
network
Cold War Era technology
to track and coordinate
many separate military
installations.
http://ed-thelen.org/SageIntro.html
•
Far more complex than any
other computer project of the
1950s
•
The first major system to run
in “real-time” – responding
immediately to requests from
its users and to reports from
its sensors.
•
SAGE had to present an upto-date and consistent
representation of the various
bombers, fighters and bases
to all its users.
•
Popularized the term "data
base" to refer to the data
underlying the many different
views allowed.
http://ed-thelen.org/SageIntro.html
Corporate Conceptions of
Databases
Robert V. Head, "Management Information Systems: A Critical Appraisal", Datamation 13, no. 5 (May 1967):22-27, page 24.
File based storage - 1968
Predecessor of databases
Advantages
Limitations
Various access methods , e.g.,
sequential, indexed, random
Requires extensive programming
Separation and isolation: Each
program maintains its own set of
data
Duplication of data – same data is
held by different programs, thus,
wastes space and resources.
High maintenance costs such as
ensuing data consistency and
controlling access
Sharing granularity is very coarse.
Weak security.
Hierarchical Database 1968-1980
Advantages
Limitations
Efficient searching.
Complex implementation
Less redundant data.
Files are related in a
parent/child manner, with each
child file having at most one
parent file.
Data independence.
Database security and integrity.
Difficult to manage and lack of
standards, can’t easily handle
many-many relationships.
Lacks structural independence.
Network Data Model - Early
1960s-1970s
Advantages
Limitations
Ability to handle more relationship System complexity and difficult to
types
design and maintain
Network data model identified the following three
database components:
Ease of data access
Network schema—database organization[structure]
Sub-schema—views of database per user
Data management language — at low level,
procedural
Data Integrity
Data Independence
Lack of structural independence as
data access method is
navigational.
Relational Databases 1970-Present
Instance – a table with rows and
columns.
Schema – specifies the structure
(name of relation, name and type of
each column)
Advantages
Limitations
Control of data redundancy,
consistency, abstraction, sharing
Complexity, size, cost of DBMS
Improved data integrity, security,
enforcement if standards and
economy of scale
Improved data accessibility and
maintenance
Higher impact of failure
Object Oriented Database 1980-Present
Advantages
Limitations
Can efficiently manage a large
number of different data types.
Switching an existing database to
OODBMS requires an entire
change from scratch.
Objects with complex behaviors
An OODBMS is typically tied to a
are easy to handle using
specific programming language
inheritance and polymorphism etc.
and an API; this reduces its
flexibility.
It supports the modeling and
creation of the data as objects.
Reduces the large number of
relations by creating objects.
Ad-hoc queries are difficult to
implement as one cannot join two
classes as one can join two tables
in RDBMS.
History of Databases
Why was the development of Hard Disks important to databases?
Larger Storage Capacity
Block Segmentation
Low Latency
Nice Hum Noise