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信息处理技术
Chapter10:
4: Computer,
1:
File
Management,
Internet,Virus
Chapter
Databases
Protection,
Web,
and E-Mail
and Backup
Basics
1
2
Chapter 10 Preview
After this chapter, you should be able to:
– Define basic database terminology, such
as fields, records, record types, and
cardinality
– Describe the characteristics of hierarchical,
network, relational, and object-oriented
databases
– Explain the capabilities of various data
management tools, such as commercial
applications, word processing software,
spreadsheet software, file management
software, and database management
Chapter 10: Databases
3
Chapter 10 Preview
– Describe various ways to provide access to
databases via the Web
– Explain how to design an effective
relational database
– Use your knowledge of SQL queries to
describe how to add records, delete
records, search for information, update
fields, and simultaneously access data
from multiple tables
Chapter 10: Databases
4
Chapter 10 Outline
• Section A
– File and Database Concepts
• Section B
– Data Management Tools
• Section C
– Database Design
• Section D
– SQL
Chapter 10: Databases
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Chapter 10
Databases
Section A: File and Database Concepts
文件及数据库的概念
Computer Concepts 8th Edition
Databases and Structured
Files: What is a database?
• A database is a collection of information
• Databases are typically stored as
computer files
• A structured file uses a uniform format
to store data for each person or thing in
the file
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Fields: What is the basic
element of a structured file?
• A field contains the smallest unit of
meaningful information
• Each field has a unique field name that
describes its contents
• A field can be either variable length or
fixed length
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Records: What is a record?
• A record refers to
a collection of
data for someone
or something
• A record is made
of fields of
individual pieces
of data for each
person or thing
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Relationships and Cardinality:
How do record types pertain to
files and databases?
• A data file that contains only one record
type is often referred to as a flat file
• In contrast, a database can contain a
variety of different record types
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What are relationships?
• An association between data that’s stored in
different record types (a field in one table can
refer to a record in another Table)
• One important aspect of the relationship
between record types is cardinality
• Cardinality refers to the number of associations
that can exist between two record types
– A particular order cannot be placed jointly by two
customers
• When one record is related to many records, the
relationship is referred to as a one-to-many
relationship
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What are relationships?
???
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What’s a relational database?
• Stores data in a collection of related
tables
• Each table (also called a “relation”) is a
sequence, or list, of records.
• All of the records in a table are of the
same record type
Not
Relationship
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What’s a relational database?
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What’s an object-oriented
database?
• Stores data as objects, which can be grouped
into object classes, and defined by attributes
and method
• A class specifies the attributes and methods
that are shared by all objects in a class
• A class attribute is equivalent to a field, and
contains the smallest unit of data
• A method is any behavior that the object is
capable of performing
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What’s an object-oriented
database?
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Chapter 10
Databases
Section B: Data Management Tools
数据管理工具
Computer Concepts 8th Edition
Data Management Software:
Are simple data management
tools available?
• The simplest tools for managing data are
software packages designed for a specific
data management task
• To use one of these tools, you just enter
your data
• The software provides menus that allow
you to manipulate your data after it is
entered
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How about a simple, generic tool
that allows me to define a file
structure?
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How about a simple, generic tool
that allows me to define a file
structure?
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Database Management Systems:
What kinds of tools are specifically
designed for creating and
manipulating databases?
• DBMS (database management system)
refers to software that is designed to
manage data stored in a database
• An XML DBMS, for example, is optimized for
handling data that exists in XML format
• An OODBMS (object-oriented database
management system) is optimized for the
object-oriented database model
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What kinds of tools are
specifically designed for creating
and manipulating databases?
• An RDBMS (relational database
management system) allows you to
create, update, and administer a
relational database
• Today’s most popular RDBMS software
also provides capability to handle object
classes and XML data
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What kinds of tools are
specifically designed for creating
and manipulating databases?
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Databases and the Web: Is it
possible to access a database
over the Web?
• The Web provides both opportunities and
challenges for accessing the information in a
database
• The Web provides an opportunity for many people
to gain access to data from many locations
• Web access is constrained by the stateless nature
of HTTP
• Web access to hierarchical, network, relational,
and object-oriented databases is
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What’s the simplest way to
provide Web-based access to a
database?
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What if I want to provide
access to current data?
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Is it possible to add and update
database records via the Web?
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How do I create server-side
programs?
• Several tools, including ASP, CGI, and PHP
help you create server-side programs
• ASP (Active Server Pages) technology can be
used to generate an HTML document that
contains scripts
• Scripts are small embedded programs that can
be designed to get user input, run queries, and
display query results
• CGI (Common Gateway Interface) provides a
non-proprietary way to create HTML pages
based on data in a database
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How do I create server-side
programs?
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XML Documents: How does XML
relate to the Web and
databases?
• XML is a markup language that allows
field tags, data, and tables to be
incorporated into a Web document
• HTML documents contain lots of
information
• XML provides tags that can be embedded
in an XML document to put data in context
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How is XML typically used
today?
• XML’s most positive contributions to data
management is the ability to add context to the
information contained in a widely diverse pool of
documents on the Web
• An XML document can also contain structured
data organized into records and fields
• Storing data in an XML document provides
several advantages
– It is “portable”
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How is XML typically used
today?
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Chapter 10
Databases
Section C: Database Design
数据库设计
Computer Concepts 8th Edition
Defining Fields: How does a
database designer know what
data to store?
• The first step in designing a relational
database is to determine what data must be
collected and stored
• A database designer might begin by listing
available data, as well as any additional data
that is necessary to produce on-screen output
or printed reports
• The next step is to organize that data into
fields
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Why are last names stored in a
different field than first
names?
• The treatment of first and last names
illustrates the concept of breaking data
into fields
• With the entire name in one field, the
database would not be able to access
individual parts of the name
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What makes each record
unique?
• A computer must have some way to
differentiate between records
• A primary key is a field that contains
data unique to a record
• Examples: SSN, RUID, not lastname
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How does a database designer
know what data types to use?
• The data that can be entered into a field
depends on the field’s data type
• From a technical perspective, a data type
specifies the way data is represented on the
disk and in RAM
• From a user perspective, the data type
determines the way that data can be
manipulated, e.g. addition
• The two most common data types are numeric
and character
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How does a database designer
know what data types to use?
•
•
•
•
•
•
•
Real, e.g. 3.14, $5.99
Integer, e.g. 0, 1, 2345
Date, e.g. 11/10/2005
Text, e.g. Gilbert, Grape (fixed length)
Logical, e.g. yes/no, on/off, opened/closed
Memo, Text with no fixed length
BLOB, binary files, e.g. MSWord.exe,
itec100.xls, me.gif
• Hyperlink, e.g. www.radford.edu/~kstevens2
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How does a database handle
computations?
• A computed field is a calculation that a
DBMS performs during processing
• An efficiently designed database uses
computed fields whenever possible
• Example: MSRP, DiscountPrice,
(Savings)
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Can a database designer
prevent people from entering
inaccurate data?
• The information supplied by reports and
processing routines is only as accurate as the
information in the database, GIGO
• Data entry errors can compromise the accuracy
and validity of a database
• Most DBMS tools that the database designer can
use to prevent some, but not all, data entry
errors, e.g. require a decimal point, 3.00, or must
be numeric
• In a case sensitive database, uppercase letters
are not equivalent to their lowercase
counterparts, e.g. Jewel, jewel, JEWEL
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Can a database designer
prevent people from entering
inaccurate data?
• Field validation rule, range $0.00 $100.00
• Pick from a list
• Look up routine
• Field format
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Normalization: How does a
database designer group fields
into tables?
• Normalization helps the database designer
create a database structure that can save
storage space and increase processing
efficiency
• The goal of normalization is to minimize data
redundancy
• The first step to grouping fields is to get an idea
of the “big picture” of the data
• Groupings correspond to the physical items
(nouns), or entities, that are tracked in the
database
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How does a database
designer group fields into
tables?
• This data redundancy not only requires
extra storage space, but also may lead to
storing inconsistent or inaccurate data
• The solution is to create separate tables
• If the designer provides fields for ordering
ten items, the database cannot handle
large orders for more than ten
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How does a database
designer group fields into
tables?
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How does a database
designer group fields into
tables?
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How does a database
designer group fields into
tables?
• If a customer orders fewer than ten, space
is wasted by having empty fields in each
record
• A one-to-many relationship exists between
an order and the ordered items
• The database designer should separate
the data into two tables such as Orders
and OrderDetails
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How does a database
designer group fields into
tables?
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What happens when the data
in a table is sorted?
• A table’s sort order is the order in which records
are stored on disk
• Sorted tables typically produce faster queries
and updates
• Queries and updates within an unsorted
database are slow
• A table’s sort key is one or more fields that are
used to specify where new records are inserted
in a table
• A table can have only one sort key at a time, but
the sort key can be changed, which is slow
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How is indexing different
from sorting?
Figure 10-36
• A database index contains a list of keys, and
each key provides a pointer to the record that
contains the rest of the fields related to that key
• An index has no bearing on the physical
sequence of records on disk
• A table can have multiple indexes, but only one
sort order
• Database tables should be indexed by any field
or fields that are commonly used as search fields
• The database designer typically creates indexes
at the time the database structure is designed
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What makes a good interface?
•
•
•
•
•
Arrange fields in a logical order
Provide visual clues, e.g. color
Provide easy-to-use controls, e.g. buttons, lists
Scroll only if absolutely necessary
Provide instructions/help, e.g. Help System,
ToolTips
• Provide appropriate Field Labels
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Designing Report Templates:
How can I display or print data
as a formatted report?
• A report generator is a software tool that provides
the ability to create report templates for a database
• A report template contains the outline or general
specifications for a report
• The template does not, however, contain data from
the database
• Data is merged into the template when you actually
run a report
• When you actually produce a report, it is based on
the data currently contained in the database table
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How does the database
designer create effective
report templates?
• The database designer can create
templates for reports that effectively
present information by observing the
following guidelines:
– Supply only the information required
– Present information in a usable format
– Information should be timely
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How does the database
designer create effective
report templates?
– Information should be presented in a clear,
unambiguous format, and include
necessary titles, page numbers, dates,
labels, and column headings
– Present information in the format most
appropriate for the audience
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How is data loaded into the
database tables?
• A conversion routine converts the data
from its current format into a format
that can be automatically incorporated
into the new database
• An import routine brings data into a
database
• An export routine copies data out of a
software package, and into the
database
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Chapter 10
Databases
Section D: SQL
数据库查询语言-SQL
Computer Concepts 8th Edition
How does a query language
work?
• Structured Query Language, SQL
• Work behind the scenes as an between
the client software provided to users, and
the database itself
• Intermediary database client software
collects your input, then converts it into an
SQL query
• An SQL query operates directly on the
database to carry out your instructions
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How does a query language
like SQL work?
SQL
Query
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What does a simple SQL
query look like?
• An SQL query is a sequence of words, much like a
sentence
– SELECT TrackTitle FROM Tracks WHERE
TrackTitle = ‘Fly Away’
• The SQL query language provides a collection of
special command words called SQL keywords
• Many SQL queries can be divided into three simple
elements that specify an action, the name of a
database table, and a set of parameters
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How does SQL specify the
action that I want carried out
in the database?
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How does SQL specify which
table to use?
• SQL keywords such as USE, FROM, or
INTO can be used to construct a clause
specifying the table that you want to
access.
• The clause consists of the keyword
followed by the name of the table
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How does SQL specify
parameters?
• The term parameter refers to the
detailed specifications for a command
• Keywords such as WHERE usually
begin an SQL clause containing the
parameters for a command
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Adding Records: How are
records added to a
database?
• The client software that you use collects
the data that you enter in the form and
generates an SQL statement using the
INSERT command, which adds your
data to the database
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Searching for Information:
How do SQL queries carry
out searches?
• One of the most common database
operations is to query for a particular
record or group of records using the
SELECT command
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Can SQL perform complex
searches?
• SQL uses search operators to form
complex queries
• Because search operators were
originally the idea of mathematician
George Boole, they are also referred to
as Boolean operators
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How does AND work in an
SQL query?
• AND (sometimes indicated by a + sign) is
used when you want to retrieve records that
meet more than one criteria
• The AND operator specifies that both of the
search criteria must be true for the record to
be selected
• SELECT CDName FROM CompactDisks
WHERE ArtistName = ‘Beyonce’
AND DiscountPrice < 10.00
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How does OR differ from
AND?
• Inclusive OR
Exclusive OR
– SELECT CDName FROM CompactDisks
WHERE (ArtistName = ‘Beyonce’
OR ArtistName = ’Destiny’s Child’)
AND DiscountPrice <10.00
• Note the use of parentheses around the
OR clause
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How does NOT work in an
SQL query?
• The NOT operator can be used to specify
a not-equal relationship
– SELECT CDName FROM CompactDisks
WHERE NOT(ArtistName = ‘Beyonce’)
• Sometimes NOT relationships are
specified using a not-equal operator, like
<> or !=, depending on the specifications
of the query language
– SELECT CDName FROM CompactDisks
WHERE ArtistName <> ‘Beyonce’
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Updating Fields: Can I change
the contents of a record?
• You can change records in a database
only if you have the rights to do so
– UPDATE CompactDisks
SET QtyInStock = QtyInStock – 1
WHERE CDName = ‘Dangerously in Love’
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Is it possible to update a
group of records?
• SQL can perform a global update that changes
the data in more than one record at a time
• It would be easier to change all of the records
with a single command
– UPDATE CompactDisks
SET DiscountPrice = 9.95
WHERE ArtistName = ‘The Rolling Stones’
• The UPDATE command means that you want to
change the data in some or all of the records
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Joining Tables: How is data
retrieved from more than one
table at a time?
• Creating a relationship between tables is
referred to as joining tables
• To take advantage of the relationship
between two tables, you first have to join
the tables
• The SQL JOIN command allows you to
temporarily join and simultaneously access
the data in more than one table
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How is data retrieved from
more than one table at a
time?
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How extensive is SQL?
• Very extensive and powerful language
• Can be used to
– Manipulate data
– Create databases, tables, and reports
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Conclusion
You should now be able to:
– Define basic database terminology, such
as fields, records, record types, and
cardinality
– Describe the characteristics of hierarchical,
network, relational, and object-oriented
databases
– Explain the capabilities of various data
management tools, such as commercial
applications, word processing software,
spreadsheet software, file management
software, and database management
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Conclusion
– Describe various ways to provide access to
databases via the Web
– Explain how to design an effective
relational database
– Use your knowledge of SQL queries to
describe how to add records, delete
records, search for information, update
fields, and simultaneously access data
from multiple tables
Chapter 10: Databases
74