Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.
By: Veronica Ong (1701317660) of class 01PCT
Task: Chapter Review of Chapter 10 from the Textbook Discovering Computers.
1. What is a
database, and how does a database interact with data and information?
A database is a collection of data organized in a manner
that allows access, retrieval, and use of that data. Data is a collection of
unprocessed items, which can include text, numbers, images, audio, and video.
For example, you can type text on a keyboard, talk into a computer’s
microphone, transfer photos taken with a digital camera to a computer, and
capture motion and sounds with a video camera and store the recordings on a
computer.
Information is processed data; that is, it is organized,
meaningful, and useful. In addition, to documents, information can be in the
form of audio, images, and video. For example, voice communications can be sent
in an e-mail message for a family member, friend, or coworker to hear. You can
post photos taken with a digital camera on a Web page for others to view. With
a Web cam, others can see you in real time during a conference call.
Computers process data in a database into information. A
database at a school, for example, contains data about its students and
classes. When a student is admitted to a school, for example, contains data
about its students and classes. When a student is admitted to a school, an
admissions department clerk enters several data items into a computer. The
clerk also uses a digital camera to photograph the new student. This photo,
along with the other entered data, is stored in a database on a server’s hard
disk. A computer at the school then processes the new student data and sends
advising appointment information to a laser printer and student ID card
information to an ID card printer. The student ID is encoded on a magnetic
stripe on the back of the ID card.
2. What is data
integrity, and what are the qualities of valuable information?
For a computer to produce correct information, the data that
is entered into a database must have integrity. Data integrity identifies the
quality of the data. An erroneous student address in a student database is an
example of incorrect data. When a database contains this type of error, it
loses integrity. The more errors the data contains, the lower its integrity.
Garbage in, garbage out (GIGO) is a computing phrase that
points out the accuracy of a computer’s output depends on the accuracy of the
input. If you enter incorrect data into a computer (garbage in) the computer
will produce incorrect information (garbage out).
Data integrity is important because computers and people use
information to make decisions and take actions. When you register for classes
and pay with a credit card, a process begins that charges an amount to your
credit card. If the per credit fee is not correct in the school database, an
incorrect amount will be billed to your credit card. This type of error costs
both you and the registration clerk extra time and effort to remedy.
The information that data generates also is an important
asset. People make decisions daily using all types of information such as receipts,
bank statements, pension plan summaries, stock analyses, transcripts, and
credit reports. At school, students use grade reports and degree audits to make
decisions. In a business, managers make decisions based on sales trends,
competitors’ products and services, production processes, and even employee
skills.
To assist with sound decision making, information must have
value. For it to be valuable, information should be accurate, verifiable,
timely, organized, accessible, useful, and cost-effective.
-Accurate information is error free. Inaccurate information
can lead to incorrect decisions. For example, consumers assume their credit
report is accurate. If your credit report incorrectly shows past due payments,
a bank may not lend you money for a car or house.
-Verifiable information can be proven as correct or
incorrect. For example, security personnel at an airport usually request some
type of photo identification to verify that you are the person named on the
ticket.
-Timely information has an age suited to its use. A decision
to build additional schools in a particular district should be based on the
most recent census report – not on one that is 20 years old. Most information
loses value within time. Some information, however, such as information about
trends, gains value as time passes and more information is obtained. For
example, your transcript gains value as you take more classes.
-Organized information is arranged to suit the needs and
requirements of the decision maker. Two different people may need the same
information presented in a different manner. For example, an inventory manager
may want an inventory report to list out-of-stock items first. The purchasing
agent, instead, wants the report alphabetized by vendor.
-Accessible information is available when the decision maker
needs it. Having to wait for information may delay an important decision. For
example, a sales manager cannot decide which sales representative deserves the
award for highest annual sales if the December sales have not yet been placed
in the database.
-Useful information has meaning to the person who receives
it. Most information is important only to certain people or groups of people.
Always consider the audience when collecting and reporting information. Avoid
distributing useless information. For example, an announcement of an alumni
association meeting is not useful to students not yet graduated.
-Cost-effective information should give more value than it
costs to produce. An organization occasionally should review the information it
produces to determine if it still is cost-effective to produce. Sometimes, it
is not easy to place a value on information. For this reason, some
organizations create information only on demand, that is, as people request it,
instead of on a regular basis. Many make information available online. Users
then can access and print online information as they need it. For example,
sending a printed benefits manual to each employee could be quite costly.
Instead, employees can access an online benefits manual, when they need to
review it.
3. What is meant by
character, field, record, and file?
A bit is the smallest unit of data the computer can process.
Eight bits grouped together in a unit comprise a byte. In the ASCII coding
scheme, each byte represents a single character, which can be a number, letter,
space, punctuation mark, or other symbol. The Unicode coding scheme, by
contrast, uses one or two bytes to represent a character.
A field is a combination of one or more related characters
or bytes and is the smallest unit of data a user accesses. A field name
uniquely identifies each field. When searching for data in a database, you
often specify the field name. Field names for the data in the instructor file
are instructor ID, first name, last name, extension, office, and web address. A
database uses a variety of characteristics, such as field size and data type,
to define each field. The field size defines the maximum number of characters a
field can contain. For example, the Instructor ID field contains 6 characters
and thus has a field of 6. The type of data in a field is an important
consideration. The data type specifies the kind of data a field can contain and
how a field is used. Common data types include text, numeric, autonumber,
currency, date, memo, yes/no (called boolean, or true/false), hyperlink, and
object.
A record is a group of related fields. For example, a
student record includes a set of fields about one student. A primary key is a
field that uniquely identifies each record in a file. The data in a primary key
is unique to a specific record. For example, the Student ID field uniquely
identifies each student because no two students can have the same Student ID.
In some tables, the primary key consists of multiple fields, called a composite
key. For example, the primary key for the Schedule of Classes file could
consist of the fields Semester Code, Class Code, and Class Section, which
together would uniquely identify each class listed in a schedule.
A data file is a collection of related records stored on a
storage medium such as a hard disk or optical disc. A student file at a school
might consist of thousands of individual student records. Each student record
in the file contains the same fields. Each field, however, contains different data.
Typical fields about people often include First name, Last name, Address, City,
State, Postal Code, and E-mail Address. A database includes a group of related
data files. With a DBMS (Database Management System), users access data and set
relationships among the data in data files.
4. What are file
maintenance techniques and validation techniques?
File maintenance refers to the procedures that keep data
current. File maintenance procedures include adding records to, modifying
records in, and deleting records from a file.
Adding records: Users add new records to a file when they
obtain new data. If a new student is admitted to the school, an admissions
department clerk adds a new record to the Student file.
Modifying records: Generally, users modify a record in a
file for two reasons to correct inaccurate data or to update old data with new
data. As an example of the first type of change, assume that an admissions
department clerk enters a student’s email address as ge@earth.net, instead of eg@earth.net. The student notices the error when
she reviews her advising appointment confirmation at home. The next time she
visits school, she requests that an admissions department clerk correct her
e-mail address. A more common reason to modify a record is to update old data
with new data. Suppose, for example, that Elena Gupta moves from 2 East Penn
Drive to 76 Ash Street. Elene Gupta’s address would have to be updated on the
database to replace the old address for the new one.
Deleting records: When a record no longer is needed, a user
deletes it from a file. Assume a student named Benjamin Tu is moving out of the
country. The student’s data would have to be deleted since it no longer is
needed, so Benjamin Tu’s record has to be deleted from the database.
Validation is the process of comparing data with a set of
rules or values to find out if the data is correct. Many programs perform a
validity check that analyzes data, either as you enter it or after you enter
it, to help ensure that it is correct. For instance, when an admissions
department clerk adds or modifies data in a student record, the DBMS tests the
entered data.
With per credit hour fee, you would expect to see numbers
before and after a decimal point. For example, a valid per credit hour fee is
220.25. An entry of 2DW.8I clearly is not correct. If the data fails a validity
check, the computer either should not allow the invalid data to be entered, or
it should display an error message that instructs the user to enter the data
again. Validity checks, sometimes called validation rules, reduce data entry
errors and thus enhance the data’s integrity. These are several types of
validity checks:
-Alphabetic/Numeric Check: An alphabetic check ensures that
users enter only alphabetic data into a field. A numeric check ensures that
users enter only numeric data into a field. For example, data in a First Name
field should contain only characters from the alphabet. Data in a Postal Code
field should contain numbers (with the exception of the special characters such
as a hyphen).
-Range Check: A range check determines whether a number is
within a specified range. Assume the lowest per credit hour fee at the school
is $75.00 and the highest is $370.75. A range check for the Credit Hour Fee
field ensures it is a value between $75.00 and $370.75.
-Consistency check: A consistency check tests the data in
two or more associated fields to ensure that the relationship is logical and
their data is in the correct format. For example, the value in a Date Admitted
field cannot occur earlier in time than a value in a Birth Date field.
-Completeness check: a completeness check verifies that a
required field contains data. For example, some fields cannot be left blank;
others require a minimum number of characters. One completeness check can
ensure that data exists in a Last Name field. Another can ensure that a day,
month, and year are included in a Birth Date field.
-Check Digit: A check digit is
a number or character that is appended to or inserted in a primary key value. A
check digit often confirms the accuracy of a primary key value. Bank account,
credit card, and other identification numbers often include one or more check
digits. A program determines the check digit by applying a formula to the
numbers in the primary key. For example, if the primary key is 1367, this
formula would add these number (1 + 3 + 6 + 7) for a sum of 17. Next, the
formula would add the numbers in the result (1 + 7) to generate a check digit
8. The primary key then is 13678. When a data entry clerk enters the primary
key of 13678, for example, the program determines whether the check digit is
valid. If the clerk enters an incorrect primary key, such as 13778, the check
digit entered 8 will not match the computed check digit. In this case, the
program displays an error message that instructs the user to enter the primary
key value again.
5. How is a file
processing approach different from the database approach?
Almost all application programs use the file processing
approach, the database approach, or a combination of both approaches to store
and manage data.
In the past, many organizations exclusively used file
processing systems to store and manage data. In a typical file processing system,
each department or area within an organization has its own set of files. The
records in one file may not relate to the records in any other file.
Organizations have used file processing systems for many years. Many of these
systems, however, have two major weaknesses: they have redundant data and they
isolate data.
When an organization uses a database approach, many programs
and users share the data in the database. A school’s database most likely at a
minimum contains data about students, instructors, schedule of classes, and
student schedules. Various areas within the school share and interact with the
data in this database. The database does secure its data, however, so that only
authorized users can access certain data items. While a user is working with
the database, the DBMS resides in the memory of the computer. Instead of
working directly with the DBMS, some users interact with a front end. A front
end is a program that generally has a more user-friendly interface than the
DBMS. For example, a registration department clerk interacts with the Class
Registration program. This front-end program interacts with the DBMS, which in
turn interacts with the database. Many programs today have a Web page as their
font end. An application that supports a front-end program sometimes is called
the backend. In this case, the DBMS is the back end.
Databases also have some disadvantages. A database can be
more complex than a file processing system. People with special training
usually develop larger databases and their associated applications. Databases
also require more memory, storage, and processing power than file processing
systems. Data in a database can be more vulnerable than data in file processing
systems. A database can store a lot of data in a single file. Many users and
programs share and depend on this data. If the database is not operating
properly or is damaged or destroyed, users may not be able to perform their
jobs. Furthermore, unauthorized users could gain access to a single database
file that contains personal and confidential data. To protect their valuable
database resource, individuals and companies should establish and follow
security procedures.
6. What functions are
common to most database management systems?
A database management system (DBMS), or database program, is
software that allows you to create, access, and manage a database. DBMSs are
available for many sizes and types of computers. Whether designed for a small
or large computer, most DBMSs perform common functions:
-Data Dictionary: a data dictionary, sometimes called a
repository, contains data about each file in the database and each field in
those files. For each file, it stores details such as the file name,
description, the file’s relationship to other files, and the number of records
in the file. For each field, it stores details such as the field name,
description, field type, field size, default value, validation rules, and the
field’s relationship to other fields. Because the data dictionary contains
details about data, some call it metadata (meta means more comprehensive).
Sometimes, a data dictionary also contains data about programs and users. It
might keep track of who accessed data and when they accessed it. The data
dictionary is a crucial backbone to a DBMS. Thus, only skilled professionals
should update the contents of a data dictionary.
-File Retrieval and Maintenance: A DBMS provides several
tools that allow users and programs to retrieve and maintain data in the
database. File maintenance involves adding new records, modifying data in
existing records, and removing unwanted records from the database. To retrieve
or select data in a database, you query it. A query is a request for specific
data from the database. Users can instruct the DBMS to display, print, or store
the results of a query. The capability of querying a database is one of the
more powerful database features. To meet the needs of wide variety of database
users, from trained experts to nontechnical staff, a DBMS offers several
methods to retrieve and maintain its data. The four more commonly used are
query languages, query by example, forms, and report generators.
-Data Security: A DBMS provides means to ensure that only
authorized users access data at permitted times. In addition, most DBMSs allow
different levels of a access privileges to be identified for each field in the
database. These access privileges define the actions that a specific user or
group of users can perform. Access privileges for data involve establishing who
can enter new data, modify existing data, delete unwanted data, and view data.
In the Schedule of Classes file, the student would have read-only privileges.
That is, the student could view the list of classes offered in a semester,
meaning he or she can view and modify the data. Finally, some users have no
access privileges to the data; that is, they cannot view or modify any data in
the database. Many organizations adopt the principle of least privilege policy,
where users’ access privileges are limited to the lowest level necessary to
perform required tasks.
-Backup and Recovery: occasionally a database is damaged or
destroyed because of hardware failure, a problem with the software, human
error, or a catastrophe such as fire or flood. A DBMS provides a variety of
techniques to restore the database to a usable form in case it is damaged or
destroyed. A backup, or copy of the entire database should be made on a regular
basis. Some DBMSs have their own built-in backup utilities. Others require
users to purchase a separate backup utility, or use one included with the
operating system. More complex DBMSs maintain a log, which is a listing of
activities that modify the contents of the database. If a registration
department clerk modifies a student’s address, for example, the change appears
in the log. A DBMS that creates a log usually provides a recovery utility. A
recovery utility uses the logs and/or backups to restore a database when it
becomes damaged or destroyed. The recovery utility restores the database using
rollforward and rollback techniques. In a rollforward, also called forward
recovery, the DBMS uses the log to reenter changes made to the database since
the last save or backup. In a rollback, also called backward recovery, the DBMS
uses the log to undo any changes made to the database during a certain period.
Continuous backup is a backup plan in which all data is backed up whenever a
change is made. This backup technique can cost more than other backup
strategies but is growing in popularity because of its benefits. Continuous
backup provides recovery of damaged data in a matter of seconds.
7. What are the
characteristics of relational, object-oriented, and multidimensional databases?
Relational databases: A relational database is a database
that stores data in tables that consist of rows and columns. Each row has a
primary key and each column has a unique name. A file processing environment
uses the terms file, record, and field to represent data. A relational database
uses terms different from a file processing system. A developer of a relational
database refers to a file as a relation, a record as a tuple, and a field as an
attribute. A user of relational database, by contrast, refers to a file as a
table, a record as a row, and a field as a column. In addition to storing data,
a relational database also stores data relationships. A relationship is a link
within the data. In a relational database, you can set up a relationship
between tables at any time. For example, you would relate the Instructor table
using the Instructor ID column.
-Object Oriented Database: stores data in objects. An object
is an item that contains data, as well as the actions that read or process the
data. A student object, for example, might contain data about a student such as
Student ID, First Name, Last Name, Address, and so on. It also could contain
instructions about how to print a student transcript or the formula required to
calculate a student’s grade point average. A record in a relational database,
by contrast, would contain only data about a student. OODB have several
advantages compared with relational databases: they can store more types of
data, access this data faster, and allow programmers to reuse objects. An
object-oriented database stores unstructured data more efficiently than a relational
database. Unstructured data can include photos, video clips, audio clips, and
documents. When users query an object-oriented database, the results often are
displayed more quickly than the same query of a relational database. If an
object already exists, programmers can reuse it instead of recreating a new
object – saving on program development time.
-Multidimensional databases: A multidimensional database
stores data in dimensions. Whereas relational database is a two-dimensional
table, a multidimensional database can store more than two dimensions of data.
These multiple dimensions, sometimes known as hypercube, allow users to access
and analyze any view of the database data. A webmaster at a retail business may
want information about product sales and customer sales for each region
spanning a given time. A manager at the same business may want information
about product sales by department for each sales representative spanning a
given time. A multidimensional database can consolidate this type of data from
multiple dimensions at very high rates of speed. The number of dimensions in a
multidimensional database varies. A retail business might have four dimensions:
products, customers, regions, and time. Nearly every multidimensional database
has a dimension of time. The content of other dimensions varies depending on
the subject. The key advantage of the multidimensional database is that it can
consolidate data much faster than a relational database. A relational database
typically does not process and summarize large numbers of records efficiently.
With a multidimensional database, users obtain summarized results very quickly.
8. How are web
databases accessed?
One of the more profound features of the Web is the vast
amount of information it provides. The Web offers information about jobs,
travel destinations, television programming, photos, movies, videos, local and
national weather, sporting events, and legislative information. You can shop
for just about any product or service, buy or sell stocks, search for a job,
make airline reservations, register for college classes, and check semester
grades. Much of this and other information exists in databases that are stored
on the Web or are accessible through the web. Some Web databases are
collaborative databases, where users store and share photos videos, recordings,
and other personal media with other registered users.
To access data in a Web database, you fill in a form or
enter search text on a Web page. The Web page is the front end to the database.
Many search engines such as Yahoo! Use databases to store Web site
descriptions. Thus, the search engine’s home page is the front end to the
database. To access the database, you enter search text into the search engine.
A Web database usually resides on a database server. A
database server is a computer that stores and provides access to a database.
One type of program that manages the sending and receiving of data between the
front end and the database server is a CGI (Common Gateway Interface) script.
CGI scripts run automatically – ass soon as you click the button to send or
receive information. Writing a CGI script requires computer programming skills.
In addition to accessing information, users provide information to Web
databases. Many Web sites request that users enter personal information, such
as name, address, telephone number, and preferences, into an e-form. The
database then stores this personal information for future use. An organization,
for example, may send e-mail messages to certain groups of customers. If you
are a frequent flyer, you may receive travel information. For smaller
databases, many personal computer database programs provide a variety of Web
publishing tools that enable users without computer programming experience to
create a home or small office database.
9. What are the
responsibilities of database analysts and administrators?
Role of the database analysts and administrators: The
database analysts and administrators are responsible for managing and
coordinating all database activities. The database analyst (DA), or data
modeler, focuses on the meaning and usage of data. The DA decides on the proper
placement of fields, defines the relationships among data, and identifies
users’ access privileges. The database administrator (DBA) requires a more
technical inside view of the data. The DBA creates and maintains the data
dictionary, manages security of the database, monitors the performance of the
database, and checks backup and recovery procedures. In small companies, one
person often is both the DA and DBA. In larger companies, the responsibilities
of the DA and DBA are split among two or more people.
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