Transcript presentation - University of Reading

Database Design
Introduction
John Wordsworth
Department of Computer Science
The University of Reading
[email protected]
Room 129, Ext 6544
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Lecture objectives
Understand how the course works and where to find the
materials.
Describe the history of the development of databases.
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Textbook
Connolly and Begg: Database Systems: A
Practical Approach to Design Implementation
and Management. Third edition, Addison
Wesley, 2002, ISBN 0-201-34287-1
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Data processing
Many applications.
Each application entirely separately.
Each design of data was closely coupled to the
design of the program.
Hard to exchange data between applications.
Every new application had to design its own
data files from scratch.
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Example
• The marketing division has a customer file
– people it sends catalogues to
• The sales division also has a customer file
– people it sends invoices to
• Sales sends invoice; customer has moved;
new address to sales; marketing continue to
send catalogues to old address.
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Data
• Information about people and things
– person (name, address, age, job-title, annual
salary)
– engine (cyls, capacity, fuel, turbo, output)
• Relationships between things
– department :: teaching-staff
– hall :: students
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More complex relationships
•
•
•
•
students :: units
flights :: airports (roles)
course delivery :: room :: lecturer (3-ary)
consultant :: patient :: illness :: treatment (4ary)
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What is a database?
• General purpose data repository
• Based on particular data model
• Managed by a DBMS that provides:
– Data Definition Language
– Data Manipulation language
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Three models of data
• Hierarchical
– designed for 1:M relationships; more complex
relationships possible but very artificial
• Network
– based on sets defined by logical links
• Relational
– based on tables
– initially believed too costly; now dominant
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Emphasis
• In hierarchical and network systems
– record navigation
• In relational systems
– specification of mathematical processes on bulk
data
– (compare the matrix in mathematics)
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The ANSI-SPARC three-layer
architecture
• External schema
– the views of the various users of the data
• Conceptual schema
– a consolidation and rationalisation of the
external schemas
• Internal schema
– a mapping of the conceptual schema on to the
physcial data management facilities
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Key points
Data processing was originally file-based.
Data is information about things and their relationships.
Modern databases are general-purpose data stores.
There are three data models supported by DBMSs.
There has been a shift of emphasis, making data independent
of applications.
The ANSI-SPARC model sets a standard for database design.
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