Transcript A First Course in Database Systems

The Worlds of Database Systems
From: Ch. 1 of A First Course in Database Systems, by J. D. Pullman and H.
Widom
Background
• Business applications of DBs
– maintaining internal records,
– presenting data to customers and clients on the WWW, and
– supporting many other commercial processes
• Scientific applications, representing data gathered
–
–
–
–
by astronomers,
by investigators of the human genome, and
by biochemists exploring the medicinal properties of proteins,
etc.
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Background
• A database management system (DBMS or a database system) is a
powerful tool for creating and managing large amount of data
efficiently and allowing it to persist over long period of time, safely.
• Capabilities of a DBMS
– Persistent storage
– Programming interface
– Transaction management
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1.1 The Evolution of Database Systems
•
The DBMS is expected to:
1.
2.
3.
4.
Allow users to create new data and specify their schema.
Give users the ability to query the data
Support the storage of very large amount of data
Control access to data from many users at once
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1.1.1 Early Database Management Systems
• The first commercial DBMS appears in late 1960’s.
– Evolved from file systems
• Providing (3), storage of large amount of data
• No direct support of query language
• Supporting (1), a limited schema for the creation of directory structures of
files
• Not satisfying (4)
• Applications of the first DBMS
– Airline reservation systems
– Banking systems
– Corporate Records
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1.1.2 Relational Database Systems
accountNo
balance
type
12345
1000 saving
67890
2846.92 checking
...
...
...
SELECT balance
FROM Accounts
WHERE accountNo=67890
SELECT accountNo
FROM Accounts
WHERE type=‘savings’ AND balance <0
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1.1.3 Smaller and Smaller Systems
• Originally large and expensive
• Today
–
–
–
–
many gigabytes fit on a single disk
feasible to run a DBMS on a PC
become available for even very small machines
a common tool for computer applications, much as spreadsheet and word
processors did before
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1.1.4 Bigger and Bigger Systems
• Corporate databases often occupy hundreds of gigabytes.
– Retails chains often store tetrabytes (1012 bytes) of information recording
the history of every sales made over a long period of time.
• Multimedia data
– An hour of video consumes about a gigabyte.
– Databases storing images from satellites can involve petabytes (1015 bytes)
of data.
• Trends allowing DBSs to deal with large amount of data
– Tertiary storage
– Parallel computing
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1.1.5 Client-Server and Multi-Tier Architectures
• The simplest client/server architecture
– the entire DBMS is a server
– the query interfaces that interact with the user and send queries or other
commands across to the server
• A trend to put more works in the client
– two tier (client/server) becoming three (or more) tiers
– The DBMS continues to acts as a server, but its client is typically an
application server, which manages
• connection to the DBS, transaction, authorization, and other aspects
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1.1.6 Multimedia Data
• Common forms of multimedia data
– video, audio, radar signals, satellite images, and documents or pictures in
various encoding
• The storage of multimedia data has forced DBMS’s to expand in
several ways.
– E.g., the operations that one performs on multimedia data are not the
simple ones suitable for traditional data forms.
– To allow users to create and use complex data operations, DBMS’s have to
incorporate the ability of users to introduce functions of their own
choosing.
– The size of multimedia objects also forces the DBMS to modify the
storage manager so that objects or tuples of a gigabyte or more can be
accommodated.
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1.1.7 Information Integration
• A large company has many divisions.
– Each has its own database of products independently of other divisions.
– These divisions may use different DBMS’s, different structures for
information, perhaps even different terms to mean the same thing or the
same term to mean different things.
• Central control is not always the answer.
• One popular approach is the creation of data warehouses, where
information from many legacy databases is copied, with the
appropriate translation, to a central database
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1.2 Overview of a DBMS
1.2.1 Data-definition language commands
1.2.2 Overview of Query processing
Answering the query
Transaction processing
1.2.3 Storage and buffer management
1.2.4 Transaction Processing
1.2.5 The query processor
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Database management
system components
Single boxes: system components
Double boxes: in-memory data structures
Solid lines: control and data flow
Dashed lines: data flow only
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1.3 Outline of Database-System Studies
• Design of databases
– Chapters 2, 3 and 4
• Database programming
– Chapters 5 through 10
• Database system implementation
– Storage management
– Query processing
– Transaction management
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