Unit 10 Database ContentsLearning ObjectivesAfter you have read this
unit, you should be familiar with:1. What is database?2. The bas
ic characters of database. ⊙Words&ExpressionsWords&ExpressionsWor
ds&Expressions⊙Text What is a Database? Databases have becom
e involved in virtually every aspect of our lives. Almost every d
ay, we encounter some kind of a database; while checking out item
s at the grocery store, making a hotel reservation, searching for
a book at the library, etc. If you''ve ever made an airline reser
vation, used an ATM machine, or made a mobile-phone call, you''ve
used a database. In fact, many cities use intelligent traffic gui
ding system databases to control stoplights. So the next time you
''re waiting at a red light, it may be a database that is responsi
ble for your delay!Text To understand how important da
tabases have become in today''s world, consider the following stat
istics:Currently 20% of the world''s data resides in RDBMSs.In the
next two years, databases are expected to grow larger than 100 t
erabytes. A database this big would be able to store 100,000 copi
es of the Encyclopedia Britannica or 200,000 hours of music or ab
out 10 billion web pages. DB So what is a database (DB)? I
t is a collection of related data. Databases have been around for
so long, and in different forms. All kinds of informa
tion (school records, credit history, shopping patterns, and groc
ery purchases) are stored in databases. It is important to unders
tand what is stored in a database and what can be retrieved from
it. The words "data" and "information" are often used as if they
are synonyms. Nevertheless, they have different meanings.
Data: Raw material, from which you can draw conclusions. Facts
from which you can deduce new facts. Information: Knowled
ge, intelligence, a particular piece of data with a special meani
ng or function. Information is often the result of combining, com
paring, and performing calculations on data.Text Whenever
a student, teacher, administrator (or any person using a computer
) interacts with a website, pieces of data are collected. The gra
phical user interface (GUI) may be unique to that school or compa
ny, but what happens “behind the scenes”? Think about te
st scores, for example. In one class, if every student receives a
numbered score, the scores can be calculated to determine a clas
s average. The class averages can be calculated to determine the
school average. The Oracle database software will transform recor
ded/stored data and statistics into useful pieces of information.
Data: Each student’s test score is one piece of data.
Information: The class’ average score, or the school’s average sc
ore.TextWhat is a database?A centralized and structured set of da
ta stored on a computer system.The database also provides facilit
ies for retrieving, adding, modifying and deleting the data when
required.The database also provides facilities for transforming r
etrieved data into useful information.A database is usually manag
ed by a Database Administrator (DBA). TextRDB A paper r
ecord of information is a database. A text file with information
in it can be considered as a database. However, the word Database
has become more likely to refer to Relational Databases; a form
of databases where data is arranged into tables, each of which co
nsists of rows and columns. From now on, the term database will b
e used to mean a relational database, unless otherwise specified.
In a relational database (RDB), data is stored in tables
(also known as relations). Each table usually represents an entit
y (an item, component, person, project, etc.). Each table has mul
tiples columns (also called fields or attributes). These columns
represent different properties of the entity represented by the t
able. For example, an employee table might have columns like name
, hire date, salary, position, department, etc. Text Each row
in that table represents one employee. Rows are also known as rec
ords or tuples. (See Figure 5-1)Figure 5-1 Employee Tablecolumns
(fields, attributes)rows(tuples)Text Now, one cannot put
all data in the same table. Why? Well, because things are differ
ent. They have different entity types. A student is not the same
as an employee. It is true that they are both persons, but each o
f them has different properties that are of interest. An employee
has a salary and a position, while a student has a major and a s
core. So, different entities are stores in different tables, with
each table containing the relevant columns (attributes) for that
particular entity. DBMS So why use databases? Why not jus
t store everything in files? Actually, even databases store data
in files on disk. However, to deal with that data, the user does
not have to know the physical structure of these files (e.g. how
the records are ordered in the file, the size of each record, etc
.) Text All the user has to know is the logical represe
ntation of the data (i.e. the table names, what columns they have
, etc.) This makes it possible to change the underlying file stru
cture completely without having to get familiar with the new stru
cture. In order to hide the underlying details, the tables an
d their structure are encapsulated within a Database Management S
ystem (DBMS). A DBMS is the external shell that the user deals wi
th when creating new tables, managing tables, dealing with the da
ta in the tables, etc. There are many popular commercial DBMSs ou
t there, such as Microsoft Access, SQL Server, DB2, Oracle, Postg
reSQL, mySQL, etc.Text DBMSs provide more flexibility wh
en developing applications that deal with the data, since the app
lications can be made to interact only with the DBMS, without wor
rying about the underlying physical details of the file system on
which the data is actually stored. In very large database system
s, many users, servers and tables make up the RDBMS. History of t
he Database Timeline1960s: Computers become cost effective for pr
ivate companies along with increased storage capability.1970-72:
E.F. Codd proposes the relational model for databases, disconnect
ing the logical organization from the physical storage.? Text 197
6: P. Chen proposes the entity relationship model (ERM) for datab
ase design.Early 1980s: The first commercially-available relation
al database systems start to appear at the beginning of the 1980s
with Oracle Version 2.Mid-1980s: SQL (structured query language)
becomes "intergalactic standard." Early 1990s: An industry shake
out begins with fewer surviving companies. Oracle survives.Mid-19
90s: Kaboom! The usable Internet/World Wide Web (WWW) appears. A
mad scramble ensues to allow remote access to computer systems wi
th legacy data.TextLate 1990s: The large investment in Internet c
ompanies helps create a tools market boom for Web/Internet/DB con
nectors.Early 21st century: Solid growth of DB applications conti
nues. Examples: commercial websites (yahoo.com, amazon.com), gove
rnment systems (Bureau of Citizenship and Immigration Services, B
ureau of the Census), art museums, hospitals, schools, etc. ⊙Text
Exercises1. Answer the following question according to the text.
(1) What differences has between the words “data” and “informatio
n”?(2) Define “database” and why is it critical to our lives?(3)
How to use databases?(4) What is the value of database?(5) What a
re the characteristics of DBMS? 2. Translate the following terms
or phrases from English into Chinese and vice versa:keyExercises
3. Fill in the blanks with the information given in the text: (1
) The ____also provides facilities for retrieving, adding, modify
ing and deleting the data when required.(2) The database also pro
vides facilities for transforming retrieved data into useful___ .
(3) A database is usually managed by a____ .(4) A centralized and
structured set of ____stored on a computer system is called data
base. (5)____ is often the result of combining, comparing, and pe
rforming calculations on data.keyExercises4. Choose the best one
from the items given below to complete the following passage.
Computer are designed to manipulate (1) in the
form of data．We give (2) and meaning to the data，we put int
o our computes through the use of data (3) which contain num
bers， (4) or both These data files are accessed by familiar
applications such as spreadsheets，Word processing programs，and
(5) ． (1) A. files B. information C. text D. wor
d(2) A. structure B. type C. bone D. memo
ry(3) A. format B. memory C. printer D. f
iles(4) A. text B. type C. word
D. files(5) A. disk B. database C. software
D. storeskeyExercises5. Mark the following statements with
T(true) or F(false) according to the text.(1) The data in a data
base are organized into tables.(2) The user has to know the logic
al representation of data.(3) In order to hide the underlying det
ails, the tables and their structure are encapsulated within a Da
tabase Management System (DBMS).(4) A DBA is the external shell t
hat the user deals with when creating new tables, managing tables
, etc.(5) Oracle is DBMS.keyExercises6. Select the one answer to
each question.(1) ____allows one or many persons to use and/or m
odify this data A. Database management system B. Databa
se C. Database system D. Database administrator(2) In a
relational database (RDB), data is stored in ___.A. view B. tab
le C. views D. tables(3) In a relational database (RDB),
each ___ usually represents an entity A. view B. table C. view
s D. tablesExercises(4) In a relational database (RDB), each ta
ble has multiples columns (also called ___). A. Rows B. records
C. tuples D. fields(5) SQL stands for___ A. Structured Question
Languages B. Structured Query LanguagesC. Structured Ques
tion Language D. Structured Query Language(6) The most c
ommon operation in SQL is the query, which is performed with the
declarative statement____. A. SELECT B.UPDATEC.DELETE D.INS
ERTkeyExercises7. Translate the following sentences into Chinese
.(1) In order to hide the underlying details, the tables and thei
r structure are encapsulated within a Database Management System
(DBMS).(2) A DBMS is the external shell that the user deals with
when creating new tables, managing tables, dealing with the data
in the tables, etc. There are many popular commercial DBMSs out t
here, such as Microsoft Access, SQL Server, DB2, Oracle, PostgreS
QL, mySQL, etc.(3) All kinds of information (school records, cred
it history, shopping patterns, and grocery purchases) are stored in databases. It is important to understand what is stored in a database and what can be retrieved from it.(4) What is a database? A centralized and structured set of data stored on a computer system.keyExercises1.略2.3. (1) database (2) information (3) Database Administrator/ DBA (4) data (5) Information4. (1) B (2) A (3) D (4) A (5) B5.(1) T (2) T (3) T (4) F (5) T6. (1)A (2) D (3) B (4) D (5) D (6) A7.(1) 为了隐藏潜在的细节，表和它们的结构，被封装在数据库管理系统（DBMS）中。(2) DBMS是一个用户进行如创建新表、管理表、处理表中数据等操作的外壳。有很多流行的商业DBMS，如Microsoft Access中 ，SQL Server ，DB2 ， Oracle ， PostgreSQL的，mySQL等。(3) 数据库中会存储各类信息（如学校记录、信用历史记录、购物模式、商品采购）。了解数据库中存储了哪些内容以及可以从数据库中检索到什么，是非常重要的。(4) 什么是数据库？存储在计算机系统中的一组集中的、结构化的数据。 |
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