Download chapter 2 literature review

CHAPTER 2
LITERATURE REVIEW
2.1
General Theories
2.1.1
Software Engineering
Software engineering “encompasses a process, a collection of
methods (practice) and an array of tools that allow professionals to
build high-quality computer software” (Pressman & Maxim, 2015, p.
14). There are many software development methods that are available,
each with its own advantages and disadvantages. By following the
guidelines and practices imposed by the software development
methods, software engineering helps programmers to build computer
software in sync with the timetable, and with high quality result that
satisfies the requirements defined by the stakeholders.
2.1.1.1 Extreme Programming
Figure 0.1 The Extreme Programming Process (Pressman
& Maxim, 2015, p.72)
According to Pearman and Goodwill (2006, p. 5),
Extreme Programming, or simply known as XP, is a type of
Agile software development method.
9
It consists of a
10
collection of core framework activities, principles, and
practices that embraces change that occurs during software
development. What differentiates XP from other agile
methodologies is the constant implementation of its core
framework activities on a daily basis.
Pressman and Maxim (2015, pp. 72-75) outlines the
four core framework activities:
1. Planning
The
planning activity begins
with
gathering
requirements from the user to enable the XP team to
understand the business flow, required output, major
features and functionality. This will eventually be called
user stories and each of these stories are assigned a
priority. The XP team then estimates the cost in
development weeks for each story. If the story requires
more than three development weeks, the story will be
broken down into simpler stories and assigned with
priority and cost.
The user and the XP team decides together on the
number of stories for the next release. When the project is
released, the XP team calculates its project velocity, which
is the number of stories implemented in that release.
During the development, the user can add new
stories, change the value of existing stories, split stories, or
even remove stories. The XP team therefore should
readjust its releases and plans accordingly.
2. Design
XP prefers a simple design rather than a complex
design. Hence, if the XP team encounters a difficult
design, the team creates an operational prototype of that
design called a spike solution. The idea behind this is to
reduce risk during the real deployment.
11
The design activity happens before and after coding
starts. As a result, XP encourages refactoring so that
design is constantly done.
3. Coding
Before the coding activity starts, the team must
develop unit tests based on the stories. These unit tests
will be used when the coding activity is complete so that it
acts as a feedback to the developers.
The core idea in this activity is pair programming
where two people work together on one computer to code.
This promotes faster problem-solving and real-time
quality check. After these programmers finish their work,
the codes are then merged.
4. Testing
The testing activity focuses on two tests. First, it
focuses on the unit tests developed in the coding activity.
These unit tests may be merged into a “universal testing
suite” and it can occur daily. This serves as an indication
of progress and can help programmers by detecting
warnings and errors early. Second, it focuses on
acceptance tests, which are developed from user stories.
This test focuses more on the overall system features and
functionality.
XP defines four core values which serve as its
foundation. Each of these values is outlined below.
1. Communication
In a software development, teams that can
communicate effectively are able to make decisions and
solve problems quickly. It can be in the form of writing,
speaking, gestures, and body posture and it can be via
email,
telephone,
communication.
2. Simplicity
documentation,
and
face-to-face
12
XP encourages teams to do their work as simple as
possible. It can be codes, documentations, and processes.
Hence, teams are focused on fulfilling user's requirements
rather than developing functionality that the user does not
want.
Simplicity
results
in
reduction
of
codes,
documentations, and processes which gives the teams
more time to develop more functionality into the system.
3. Feedback
Feedback helps the teams to evaluate their work. In
XP, feedback needs to be done frequently. In addition,
feedback ensures that the teams deliver high quality and
stable result.
4. Courage
XP teams have to have the courage to try something
new and embrace change. Furthermore, courage may also
expose the programmers' weakness when they are pair
programming.
Furthermore, XP has fundamental principles that are
based on the four values and these principles are more
concrete and practical than the values. Each of these
principles is outlines below.
1. Allow Rapid Feedback
This principle means that the feedback is returned to
the XP team as quickly as possible. Acceptance tests
provide the business with rapid feedback within days or
weeks and unit tests provide the developers with rapid
feedback within seconds or minutes.
2. Assume Simplicity
This principle encourages the developers to solve
every problem with simplicity. Hence, developers only
add more complexity when needed in the future.
3. Make Incremental Changes
13
This principle means that every new releases has
small change compared to the older release. This helps
developers identify problems and boost confidence. If the
change is large and there is a problem, developers will
have to search through a large area of code.
4. Embrace Change
Developers need to prepare for changes in the
requirements, not fear them. For example, if in one of the
meetings
the user changes
the requirements,
the
developers need to embrace this changes and work on the
new requirements.
5. Deliver High-Quality Work
The developers always have to insist on delivering
only high-quality work. This ensures that the work is
stable and bug-free.
2.1.2 Web-based Applications
Web-based applications, otherwise known as WebApps,
provide stand-alone function to end users. In addition, WebApps
integrate with corporate databases and business applications
(Pressman & Maxim, 2015, p. 9). Webapps were born because of the
increasing
popularity
of
HTML,
which
eventually
enabled
programmers to merge computing capability with informational
content. The characteristics of Webapps are that it is deployed in a
server and uses web browser as a client to access it. Some example of
Webapps are Google Docs, Google Voice, Mint, and Hulu.
The advantages of Webapps are (Bartz, 2015, p. 538):
-
Web browser based and platform independent
-
Very limited or no client-side updates
-
Centralized web-side updates
-
Enables users to work from any location
-
Requires no client-side installation
-
The data is centralized
14
2.1.3
Human Computer Interaction
Human Computer Interaction is a field of study that deals with
the design, implementation, and evaluation of user interface between
people and computers. There are two guidelines that is followed in this
thesis: the 8 golden rules of interface design and the 5 measurable
human factor.
2.1.3.1
Eight Golden Rules of Interface Design
In order to design a typical user interface, according to
the principle in designing user interface which is known as
the Eight Golden Rules (Schneiderman & Plaisant, 2010, pp.
88-89), consists of:
1. Strive for consistency
It is very important for interface designer to manage
the consistency of the interface design in order to prevent
user from confusion. Identical design should be used in
application menus and screens.
2. Cater to universal usability
The interface design should be well-suited to any
kind of users. Some application may only be used by
expert users, yet at least end-users should know how to
interact with the application. Adding explanations for
users can enrich the interface design and improve
application quality.
3. Offer informative feedback
For every user action within the application, there
should be some system information and feedback to avoid
user’s confusion.
4. Design dialogs to yield closure
The concatenation of actions should be grouped
together in order to help user recognize to know the
15
beginning, middle, and end of those actions. It is necessary
to give an informative feedback at the end of the actions.
5. Prevent errors
The interface of an application should display its
design as understandable as possible for user to prevent
user from making mistakes. If user suddenly makes an
error, the interface should provide simple and directive
information for recovery.
6. Permit easy reversal of actions
Actions should be reversed in order to encourage
user to explore unfamiliar options. So users can freely
explore the uncommon actions since they have known it
could be undone.
7. Support internal locus of control
Provide the sense that users are in charge of the
interface and the interface responds to their actions.
8. Reduce short-term memory load
Prevent the interface where user needs to remember
the position or information from one place to another
place.
2.1.3.2 Five Measurable Human Factor
According to Shneiderman and Plaisant (2010, p. 32),
there are five usability measures:
1. Time to learn
Time to learn is the amount of time that user needs
to learn the used of an action of a set of tasks.
2. Speed of performance
Speed of performance is specified by the amount of
time the tasks is done by user.
3. Rate of errors by users
Rate of errors is specified by the amount of errors
that users did while doing a task.
4. Retention over time
16
It is measured by the user’s ability to maintain their
knowledge about a certain task on an amount of time.
5. Subjective satisfaction
Subjective satisfaction is measured by user’s
satisfaction about the various aspects of the interface. It
can be gathered by doing some interviews or written
surveys.
2.1.4
Data
Data are “raw facts about people, places, events, and things that
are of importance in an organization” (Whitten & Bentley, 2007, p. 21).
The data that is captured is meaningless until it gets combined, filtered,
organized, and analyzed to produce valuable information.
2.1.5
Database
Connolly and Begg (2014, p. 63) refer to the database as “a
shared collection of logically related data and its description, designed
to meet the information needs of an organization”. The database is a
single place that can be used concurrently by multiple users or
departments. Hence, in an organization, it can be used to share
corporate resources across all departments.
2.1.5.1 Database Components
2.1.5.1.1
Data Definition Language
Connolly and Begg (2014, p. 90) explained
that Data Definition Language (DDL) is a
language used to describe and name the entities,
attributes, and relationships, together with any
integrity constraints. Some examples of DDL are:
1. CREATE: to create new object to the
database,
2. ALTER: to change the structure of objects
from the database,
3. DROP: to delete objects from the database.
17
The data stored in the database may need to
satisfy certain integrity constraints. Silberschatz,
Korth, and Sudarshan (2011, pp. 11-12) defines
four types of integrity constraints:
1. Domain constraints: a domain contains all
sets of values that are permitted in an
attribute. This is the most basic form of
integrity constraints and they are tested
easily by the system whenever a new data
item is inserted.
2. Referential integrity: it means that a value
that appears in an attribute of a table also
appears as a value in another attribute of
another table. An example of referential
integrity is a foreign key. When a
referential integrity constraint is violated,
the normal procedure is to reject the action
that caused the violation.
3. Assertions: it means that any condition that
the database must always satisfy. Domain
constraints
and
referential
integrity
constraints are special forms of assertions.
Other constraints that cannot be expressed
by these two constraints can be created
using assertions. For example, “every
school department must have at least five
courses offered every semester” must be
expressed as an assertion. When an
assertion is created, the system tests it for
validity. If the assertion is valid, then any
future modification to the database is
allowed only if it does not cause that
assertion to be violated.
4. Authorization: the users who access the
18
database may have different access levels.
These differentiations are expressed in
terms of authorization.
2.1.5.1.2
Data Manipulation Language
Connolly and Begg (2014, pp. 90-91)
defined Data Manipulation Language (DML) as a
language that is used to manipulate data in the
database. Some examples of DML are:
1. INSERT INTO: to insert a data into the
database,
2. SELECT: to retrieve data from the database,
3. UPDATE: to modify data in the database,
4. DELETE FROM: to delete data from the
database.
There are two types of DML:
1. Procedural DML: a language that enables the
user to tell the system what data is needed and
how to retrieve such data.
2. Nonprocedural
DML
(also
known
as
declarative DML): a language that enables the
user to tell the system what data is needed
without telling it how it is retrieved.
2.1.5.1.3
Stored Procedure
Stored procedure is a set of instructions that
can take parameters, be invoked, and perform a
particular task (Connolly and Begg, 2014, p.
280). They are used to encapsulate a group of
statements. These parameters have its own name
and data type and it can be specified as IN
parameter,
parameter.
OUT
parameter,
or
IN
OUT
19
2.1.5.2 DBMS
According to Connolly and Begg (2014, p. 64), DBMS
is “a software system that enables users to define, create,
maintain, and control access to the database”. DBMS
provides the following activities:
1. It allows users to define the database.
2. It allows users to insert, update, delete, and retrieve data
from the database.
3. It provides controlled access to the database. For example,
it may provide:
a. A security system: to prevent unauthorized users
accessing the database,
b. An integrity system: to maintain the consistency of
stored data,
c. A concurrency control system: allowing shared access
of the database,
d. A recovery control system: a system used to restore the
database to an earlier, more stable state in the event of a
hardware or software failure,
e. A user-accessible catalog: containing descriptions of
the data in the database.
The DBMS environment consist of five major
components: hardware, software, data, procedures, and
people, as illustrated in Figure 2.2.
Figure 0.2 The DBMS Environment (Connolly & Begg,
2014, p. 66)
1. Hardware: The DBMS and its application require
hardware to run. The hardware ranges from a personal
computer to a mainframe. The hardware requirements
20
depend on the needs of the organization and what DBMS
is used. Some DBMS only run on a particular hardware or
operating system, while others run on many hardware and
operating systems.
2. Software: The software component covers the DBMS
software itself and other application programs, along with
the operating system, including network software if
DMBS is being used over a network. These application
programs are typically written in a third-generation
programming language, such as C, C++, C#, Java, Visual
Basic, COBOL, Fortran, Ada, or Pascal, or a fourthgeneration language such as SQL, embedded in a thirdgeneration language.
3. Data: Data is arguably the most important component of
the DBMS environment. In Figure 2.2, data acts as a
bridge between the machine components and the human
components. The database contain both the operational
data and the metadata.
4. Procedures: Procedures are the instructions and rules that
control the design and use of the database. The users or
staff who manage the database require documented
procedures on how to use the system.
5. People: People are the final component involved in the
system. There are four types of people that are involved in
the DBMS environment:
a. Data Administrator (DA) and Database Administrator
(DBA)
DA is responsible for the management of the data
resource. The DA together with senior managers to
make sure that the database development supports
corporate objectives.
DBA is responsible for the physical realization of
the database. The DBA deals more in the technical
aspect than DA.
21
b. Logical and Physical Database Designer
Logical database designer is responsible for
identifying the data, the relationships between the data,
and the constraints of the data that will be stored in the
database.
Physical database designer is responsible for
physically realizing the logical database design.
c. Application Developer
Application
developer
is
responsible
for
implementing the application programs using all of the
requirements needed by the end-users.
d. Naive and Sophisticated End-User
Naive users are users who do not understand
DBMS and how to operate DBMS. They usually access
database using application programs.
Sophisticated users are users who are familiar the
structure of the database and all the capabilities offered
by the DBMS.
2.1.5.2.1
Advantages of DBMS
There are several advantages of using
DBMS (Connolly & Begg, 2014, pp. 75-78):
1. Storing data in a database eliminates data
redundancy by integrating the files. Hence,
multiple copies of the same data are not stored.
As a result, the risk of inconsistencies are
reduced.
2. It gives more information from the same
amount of data.
3. The database belongs to the entire organization,
so all of the data inside the database can be
shared by all authorized users.
4. It
improves
data
constraints to data.
integrity by enforcing
22
5. It improves security by protecting the database
from unauthorized users.
6. It
allows
the
enforcement
of
necessary
standards, which includes naming conventions,
documentation standards, update procedures,
and access rules.
7. It reduces cost since all departments work on
one source of data.
8. It increases productivity by providing many
standard functions that programmers would
need to code in a file-based application.
9. It
improves
maintenance
through
data
independence, a process that separates the data
descriptions from the applications. Hence,
applications become immune to changes in the
data descriptions. This cannot be achieved in
file-based systems as a change on data require
many changes to the programs that are
involved.
10.
It provides database concurrency access,
which file-based systems cannot do.
11.
It provides data backup and recovery
features to protect data from failures.
2.1.6
Intranet
Intranet is a web site or group of sites belongs to an organization
and accessible only by the members of the organization (Connolly &
Begg. 2014, p. 1050). In other words, intranet is a closed network, only
private members on a company can access the document sources inside
the local host. Intranet has same function as internet includes
exchanging email, publishing web pages, sharing multimedia files but
only in a specific closed network. Intranet is useful for organizations
since it is “... much less expensive and manageable than private
23
networks based on proprietary protocols.” (Connolly & Begg. 2014, p.
1050).
2.1.7 World Wide Web
World Wide Web (WWW) or web is a system that links
documents and/or information through hyperlinks and accessed via
internet. The information is stored as web page. The web page may
contain text, image, video, audio, and any other multimedia format.
Web has several advantages such as distributed data, freedom and
decentralization of publication, a “missing isn’t broken” open-world
philosophy, lack of centralized control, evolvability, and scalability
(Dutton & Jeffreys, 2010, p. 100).
2.1.8
URL
URL (Uniform Resource Locator) is a set of characters according
to a certain standard that is used to point a certain document (in web
page format) in the internet. According to Connolly and Begg definition
(2014, p. 1057) URL is “a string of alphanumeric characters that
represents the location of address of a resource on the internet and how
that resource should be accessed”. The URL syntax consists of three
basic parts which are the connection protocol, the host name, and the
path name where resource can be found.
2.1.9
URI
URI stands for Uniform Resources Identifiers which definition is
the generic set of all names/addresses that refer to internet sources
(Connolly & Begg, 2014, p. 1057). URI enables interaction within
World Wide Web using a specific protocols. URI can be categorized as
URL (Uniform Resource Locator) and URN (Uniform Resource
Name).
2.1.10 HTTP
HTTP as the abbreviation of Hypertext Transfer Protocol is the
protocol that is used to transfer web pages through the internet. HTTP
24
defines the client-server communication manner. HTTP transaction
consists of several stages (Connolly & Begg. 2014, p. 1053):
1. Connection: stage where the client assign a connection with the
web server
2. Request: stage where the client sends request message to web
server
3. Response: stage where the web server sends response answered
client's request
4. Close: stage where connection between client and server is
terminated.
2.1.11 HTML
Robbins (2012, p. 12) explained that “HTML (HyperText
Markup Language) is the language used to create web page
documents”. HTML is a markup language, not a programming
language. This means that it can be used to identify the various
components that make up the document. Some examples of these
components are headings, paragraphs, or lists.
Figure 0.3 Example of an HTML File (Duckett, 2011, p.20)
Figure 2.3 shows an example of HTML document. The HTML
codes are written in blue and consist of characters placed inside angle
brackets called HTML elements. Each element generally consists of
two tags: an opening tag and a closing tag. The closing tag has an
25
extra forward slash before the character. For instance, the opening tag
<h2> has a closing tag of </h2>, and the opening tag <body> has a
closing tag of </body>.
Figure 0.4 Example of an HTML Element with Attribute
(Duckett, 2011, p.25)
Some of HTML elements may have additional attributes
associated with them. According to Duckett (2011, p. 25), “attributes
provide additional information about the contents of an element”.
They are written inside the opening tag and consist of a name and a
value, separated by an equal sign. Figure 2.4 shows an element <p>
with attribute lang and this attribute has a value en-us.
2.1.12 Web Browser
A web browser is a software program that enables users to
access and view websites. Some of the most popular web browser
available for personal computers are Internet Explorer, Firefox, Opera,
Safari, and Google Chrome (Shelly & Vermaat, 2011, p. 81).
2.1.13 Web Server
According to Whitten and Bentley (2007, p. 487), web server is
“a server that hosts internet or intranet web sites”. A web server is
used to store a website. Web server can store more than one website.
By uploading website to web server, website can be accessed through
any computer connects to the network.
26
2.1.14
Entity-Relationship Diagram
Entity-relationship diagram (ERD) is “a data model utilizing
several notations to depict data in terms of the entities and
relationships described by that data” (Whitten & Bentley, 2007, p.
271). ERD is one of the tools used for data modeling. ERD consists of
three basic components: entity sets, attributes, and relationship sets.
1. Entity
Entity is a class about which its data needs to be maintained.
It represents a group of objects with the same characteristics
(Connolly & Begg, 2014, p. 406). Some example of entities can be
found on the following:
a. Persons: employee, student, supplier;
b. Places: building, branch office, campus;
c. Objects: product, book, machine;
d. Events: class, flight, order;
e. Concepts: stock, fund, bond.
Every entity has a data occurrence. Every single occurrence
of an entity is called entity instance. For example, an entity called
student may have many instances: Andy, Sue, Michael, and Tom.
In the diagram, entities are represented by a rectangle. The
name of the entity, which is a singular noun, is written on the upper
part inside the rectangle.
2. Attributes
Attributes are any properties or characteristics that describe
the entity. Some example of attributes can be found on the
following:
a. Student: name, address, gender, major, GPA;
b. Vehicle: type, brand, color, weight, horsepower;
c. Book: name, year, publisher, edition, ISBN;
d. Room: number, capacity, floor;
e. Class: course code, credit, lecturer, time.
Attribute can be characterized by the following types
(Silberschatz, Korth, & Sudarshan, 2011, pp. 267-268):
a. Simple and composite attributes
27
Attributes that has not been and cannot be divided
into subparts is called simple attributes. On the other
hand, attributes that can be broken down into other
attributes are called composite attributes. For example, a
student’s name may have a composite attribute that
consists of first name, middle name, and last name.
b. Single-valued and multivalued attributes
Attributes that only have one value for every entity
instance is called single-valued entity. For example, the
student ID attribute refers to a single student entity.
Conversely, attributes that have more than one value for
each of its entity are called multi-valued attributes. For
instance, an instructor entity may have more than one
phone numbers.
c. Derived attributes
Derived attributes are attributes that its value can be
computed from the value of other attributes. For instance,
the value of attribute age of a student entity can be
calculated from the difference between the value of
attribute date of birth and current date.
An attribute or a group of attributes that is unique and helps to
distinguish between entity instances is called a key or an identifier. An
entity may have more than one key that can differentiate its entity
instance. Each of these keys are called candidate key. One of the
candidate keys that is commonly used will eventually be chosen as a
primary key. A primary key cannot contain a null value. The
remaining candidate key that is not chosen as a primary key are called
alternate key or secondary key.
An attribute that is not a primary key in an entity but appears as
a primary key in another entity is called a foreign key. Foreign keys
must satisfy referential integrity constraint, which states that the value
of an attribute in an entity relies on the value of the same attribute in
another entity.
28
In the diagram, each of the attributes are written after the entity
name. Figure 2.5 is an example of a student entity along with its
attributes. The primary key is written directly after the entity name.
All of the foreign keys, if exist, are then written after the primary key.
The rest of the attributes are written below the foreign key. Every
primary key is marked with PK while every foreign key is marked
with FK.
Figure 0.5 Example of a Student entity (Valacich, George, &
Hoffer, 2012, p. 200)
3. Relationship
A relationship “is a natural business association that exists
between one or more entities” (Whitten & Bentley, 2007, p. 275).
All relationships are bidirectional, which means that they can be
interpreted in both directions.
Each relationship must show the number of occurrences
between the entities. This is called cardinality, which displays the
minimum and maximum occurrences of an entity that are related to
a single occurrence of other entity. The notations for cardinality
can be found on Figure 2.6.
In the diagram, relationships are represented by a line from
one attribute of an entity to another attribute of other entity. The
attribute can only be either primary key or foreign key. If on one
end is a primary key, the other end must be a foreign key and vice
versa.
29
Figure 0.6 Cardinality Notations (Whitten & Bentley, 2007, p.276)
2.1.15
Data Flow Diagram
Data flow diagram (DFD) is a diagram “that depicts the flow of
data through a system and the work or processing performed by that
system” (Whitten & Bentley, 2007, p. 317). DFD is considered as
process modeling. There are four symbols used in DFD.
1. External Agent
An external agent is a person, an organization unit, another
system, or another organization that interacts with the system and
lies outside the system (Whitten & Bentley, 2007, p. 319). It is the
origin or destination of the data (Valacich, George, & Hoffer, 2012,
p. 156). External agent can also be called external entity, source (as
it is the origin of the data), or sink (as it is the destination of the
data).
All external agents within DFD are considered outside the
system. Therefore, the following things are not considered:
30
a. Interactions between sources and sinks,
b. What sources or sinks do with the data,
c. How to redesign the sources or sinks because they are fixed,
d. How to create a direct access to stored data for sources and
sinks because they are prohibited to do such things and have
to involve processes within the system.
In the diagram, external agents are represented with squares.
The DeMarco/Yourdon equivalent for external agents are
rectangles. They are illustrated in Figure 2.7.
External
External Agent
Agent
Figure 0.7 External Agent Symbols
2. Data Store
Data store is data at rest which is captured for later use. It is
also called file and database.
Data store should describe things that is needed in the system.
Some example can be found on the following:
a. Persons: customer, department, instructor;
b. Places: building, room, campus;
c. Objects: book, product, vehicle;
d. Events: class, flight, sale;
e. Concepts: account, course, fund, stock.
If data modeling such as entity-relationship diagram (ERD) is
complete before process modeling, the data identification follows
this rule: “There should be one data store for each data entity on an
entity relationship diagram” (Whitten & Bentley, 2007, p. 320).
31
In the diagram, data stores are represented by the open-end
box. The DeMarco/Yourdon equivalent for data stores are double
lines enclosing the data store name. They are illustrated in Figure
2.8.
Data Store
Data Store
Figure 0.8 Data Store Symbols
3. Process
Process is the work performed on incoming data. A process is
the same as a system.
In the diagram, processes are represented by the rounded
rectangle illustrated in Figure 2.9. The DeMarco/Yourdon
equivalent for processes are circles.
Process
Process Name
Name
Figure 0.9 Process Symbols
A system that is complex is usually too difficult express as a
single process. As a result, it becomes too difficult to understand.
Hence, the system can be broken down into smaller subsystems.
This technique is called decomposition. An example of this
technique is illustrated in Figure 2.10.
32
Figure 0.10 System Consists of Subsystems and Processes
(Whitten & Bentley, 2007, p.322)
4. Data Flow
Data flow “represents an input of data to a process or the
output of data from a process” (Whitten & Bentley, 2007, p. 325).
The data that travels in a single data flow can be more than one and
they should be descriptive nouns and noun phrases that are
singular. Furthermore, data flow should have a name.
A data flow from a data store to a process means that the data
is retrieved to be viewed. On the other hand, a data flow from a
process to a data store means that the data is to be created, updated,
or deleted in the data store. In addition, all data flows should start
and/or end at a process.
In the diagram, data flows are drawn in solid line with arrow.
An illustration of data flow is shown in Figure 2.11.
Data Flow Name
Figure 0.11 Data Flow Symbol
DFD may have a different complexity depending on the
system. Hence, DFD can be broken down into different levels to
33
properly describe the flow within the system. The DFD that shows
the entire system as one process is called context diagram. In other
words, a context diagram shows the system boundaries, the
external agents, and the data travelling between them (Valacich,
George, & Hoffer, 2012, p. 158). In context diagram, this one
process is usually numbered “0”. An example of a context diagram
is illustrated in Figure 2.12.
Figure 0.12 Example of DFD Context Diagram (Valacich,
George, & Hoffer, 2012, p.158)
After context diagram, the DFD that are used to describe
more of the process, data flows and data stores inside the system is
level-0 diagram. In this diagram, each process’s number ends with
.0. An example of a level-0 diagram is illustrated in Figure 2.13.
34
Figure 0.13 Example of DFD Level-0 Diagram (Valacich,
George, & Hoffer, 2012, p.159)
When drawing DFD, there are some rules that must be
complied. These rules are shown on Figure 2.14. Each of these
rules are explained on the table below.
Table 0.1 Rules in drawing DFD
Rule Explanation
A
A process cannot have only outgoing data flows. If the
object only have outgoing data flows, then this object is
an external agent (or source).
B
A process cannot have only incoming data flows. If the
object only have incoming data flows, then this object is
an external agent (or sink).
D
Data flow cannot move directly between one data store to
another. Instead, this movement of data must involve a
35
process.
E
Data cannot move directly from an external agent to a
data store. Instead, this movement of data must involve a
process.
F
Data cannot move directly from a data source to an
external agent. Instead, this movement of data must
involve a process.
H
Data cannot move directly between two external agents.
Instead, this movement of data must involve a process.
J
Data flow cannot have bidirectional arrow. The data must
be separated into two data flows: one from process to data
store and another in an opposite direction.
K
Data that flows from one process to many processes must
have the same data.
L
Data flow that joins another data flow must have the same
data.
M
Data flow cannot move from one process and ends up in
that same process. The data flow must move to a different
process and produce another data flow. This new data
flow can then move to the first process.
36
Figure 0.14 Incorrect and Correct Ways to Draw DFD (Valacich,
George, & Hoffer, 2012, p.161)
37
2.1.16
Black-Box Testing
Black-box testing enables programmers and developers to derive
sets of input conditions that fully utilizes all functional requirements
for a program (Pressman & Maxim, 2015, p. 509). It attempts to find
errors in the following categories:
1.
Incorrect or missing functions,
2.
Interface errors,
3.
Errors in data structures or external database access,
4.
Behavior or performance errors,
5.
Initialization and termination errors.
38
2.2
Specific/Thematic Theories
2.2.1
PHP
PHP stands for PHP Hypertext Preprocessor. According to
Welling and Thomson (2008, p. 2), it is a server-side scripting language
designed for web development. PHP codes can be merged inside an
HTML page, and these codes are interpreted by PHP-supported web
server. PHP can also be used to generate HTML codes, enabling
developers to create a dynamic web page.
According to Powers (2010, p. 3), the process when a PHPembedded HTML page is accessed is shown on Figure 2.15. First, the
computer’s browser sends a request to the web server via the internet.
Second, The PHP-enabled web server receives and passes the request to
the PHP engine embedded in the server. Next, the PHP engine
interprets the code and, if necessary, connects to the database to
perform queries. Finally, the server sends the finished page to the
browser.
Figure 0.15 Web Server Builds Response to a Request (Powers,
2010, p.3)
2.2.1.1 Advantages of PHP
According to Welling and Thomson (2008, pp. 4-5),
some of the advantages of using PHP are:
1. Performance: PHP is very fast.
2. Scalability: PHP uses a “shared-nothing” architecture,
which means that implementation of horizontal scaling
can be implemented effectively and cheaply.
3. Interfaces within many different database systems: PHP
can connect to many popular database systems.
39
4. Low cost: PHP is free.
5. Ease of learning and use: PHP is a high level
programming language as it is primarily based on C and
Perl.
6. Portability: PHP is available for many operating systems.
2.2.2
CSS
CSS stands for Cascading Style Sheet and, according to Robbins
(2012, p. 207), is the W3C (World Wide Web Consortium) standard for
defining the presentation layer of HTML or any XML documents. The
presentation layer controls how the page is displayed on the browser.
CSS has its own language and therefore, has its own syntax.
Robbins (2012, p. 12) also mentions that CSS provides methods
for controlling how the documents look on screens other than
traditional desktop computers, such as smartphones or tablets.
Furthermore, it also has rules for specifying the non-visual presentation
of documents.
2.2.2.1 Advantages of CSS
According to Olsson and O’Brien (2008, p. 3), there are
several advantages of using CSS for the presentation layer:
1. All of the pages’ styles are kept in a limited number
of style sheets.
2. The style sheet can be cached by browsers after the
first request and can be reused by other pages, hence
bandwidth can be saved.
3. The separation of content and presentation layer
makes content reuse easier.
4. Separate styling rules can be used for different
output media.
2.2.3
Bootstrap
Bootstrap is an open-source front-end framework designed to help
programmers and developers build the user interface of websites.
40
Bootstrap was developed by Mark Otto and Jacob Thornton (Spurlock,
2013, p. 1). It consists of HTML, CSS, and Javascript code templates
for typography, form, buttons, navigation, optional Javascript
extensions, and other interface components. Additionally, Bootstrap
also supports both HTML5 and CSS3 (Bedi, 2014). The reasons why
Bootstrap framework is preferred are outlined below:
1. Easy to get started;
2. Great grid system;
3. Base styling for most HTML elements such as typography,
tables, forms, buttons, images, and icons;
4. Extensive list of components;
5. Bundled Javascript plugins.
2.2.4
Bootstrap Table
Bootstrap table is an extension of the established Bootstrap
framework. It was developed by Wen Zhi Xin and it provides a
template for table with many features such as radio, checkbox, sort, and
pagination that the basic Bootstrap framework does not have.
2.2.5 AJAX
AJAX stands for Asynchronous Javascript and XML. It is not a
programming language; it is a data-transfer mechanism. It combines
client-side programming via Javascript with XML-formatted data and
server-side programming. In addition, XHTML and CSS may also be
used for the presentation layer of AJAX-enabled elements (Welling &
Thomson, 2008, p. 856).
In a traditional webpage, when the data is retrieved from the
server and needs to be shown on the page, the whole page has to be
reloaded. This causes the user experience to become slower. AJAX
eliminates this problem as the client-side programming invokes the
server-side programming in a specific part of the page. As a result, only
a portion of the page is reloaded (Robbins, 2012, p. 497).
41
2.2.6 jQuery
According to Chaffer and Swedberg (2013, pp. 8-10), jQuery is a
free and open source library that provides a general-purpose abstraction
layer for common web scripting and as a result, jQuery is useful when
scripting is needed. jQuery is built using Javascript and it is extensible,
meaning that jQuery can be developed to add new abilities not
previously available. The capabilities that jQuery can do are:
1. Accessing elements in a document
Before the inception of jQuery, developers need to writes
many lines of code to locate part of the HTML's document.
With jQuery, developers can retrieve the exact piece of the
document that needs to be inspected or manipulated easily.
2. Modifying the appearance of a web page
jQuery helps developers by establishing the same
standards support across all browsers, a feature that CSS
cannot do. Moreover, jQuery can alter the style properties to a
part of the document even after the page has been rendered.
3. Altering the content of a document
jQuery can modify text, insert or swap images, reorder
lists, rewrite and extend HTML structure with a few lines of
code.
4. Responding a user's interaction
jQuery can respond to a wide variety of events to avoid
cluttering the HTML document with event handlers. Its eventhandling API also removes browser inconsistencies that
burden developers.
5. Animating changes being made to a document
jQuery provides interactive behaviors in the form of
visual feedback by providing many effects such as fades and
wipes. There is also a toolkit for creating a new effect.
6. Retrieving information from a server without refreshing a page
This mechanism uses Asynchronous JavaScript and
XML (AJAX). The jQuery removes browser complexity in the
client-side, enabling developers to focus on the server-side.
42
7. Simplifying common JavaScript tasks
jQuery provides enhancements to basic Javascript
operations such as iteration and array manipulation.
All of the capabilities above can be achieved because jQuery
utilizes the following strategies:
1. Leverage knowledge of CSS
jQuery employs the same mechanism for locating
elements like those on CSS. Hence, if programmers want to
add behaviors to their pages, they need to understand CSS.
2. Support extensions
To keep the library size small and avoid “feature creep”,
new plugins are developed as modules. In other words, new
plugins are not merged with the basic jQuery library. Hence,
developers can add additional plugins if needed or remove
unused plugins.
3. Abstract away browser quirks
The numerous web browsers that are available may have
its own interpretations from the defined standards. This makes
it even harder for programmers to develop a browserindependent code. jQuery adds an abstraction layer to regulate
common tasks and simplify the codes.
4. Always work with sets
All methods in jQuery are designed to work on sets of
elements rather than individual elements. Hence, if we need to
find all elements within a class, we do not have to loop through
every elements within that class. This technique is called
implicit iteration.
5. Allow multiple actions in one line
jQuery uses a programming pattern called chaining,
meaning that an element can undergo a multiple methods in a
single statement. This reduces repetition and overuse of
temporary variables.
43
2.2.7
jqPlot
jqPlot is a jQuery plugin to generate pure client-side javascript
charts in web pages (Leonello, 2011). It was conceived, developed, and
mantained by Chris Leonello since 2009. This plugin can be used to
render data into various charts: bar chart, line chart, bubble plot, pie and
donut chart etc. This plugin also supports JSON data format and AJAX
to load the data.
2.2.8 PHPExcel
PHPExcel is a free and open source PHP library that contains a
set of classes used to write or read many different spreadsheet file
formats (Baker, 2014). Some of the formats supported are Excel .xls,
Excel 2007 .xlsx, CSV, and HTML. This library is built using
Microsoft’s OpenXML standard.
2.2.9
TCPDF
TCPDF is a free and open source PHP library that contains a set
of classes for generating PDF documents (Asuni, 2005). It was released
in 2005 by Nicola Asuni. TCPDF provides complete support for UTF-8
Unicode, right-to-left languages, 1D and 2D barcode generation, and
256-bit document encryption.
2.2.10 JSON
JavaScript Object Notation or JSON is a text-based, lightweight,
and human-readable data interchange format used for data exchange
between clients and servers. It was developed by Douglas Crockford.
Although derived from Javascript and similar to Javascript objects,
JSON is not dependent on Javascript. Furthermore, JSON is languageindependent, which means that JSON can be used with all popular
programming languages such as C#, PHP, Java, C++, Python, and Ruby
(Sriparasa, 2013, p. 17). Figure 2.16 below is an example of data in
JSON format.
44
Figure 0.16 Example of Data in JSON Format
2.2.11
Javascript
Javascript is lightweight yet powerful scripting language that
enables interactivity and custom behaviors to objects on websites. It is
a client-side language, meaning that it is executed on the user’s
browser rather than on the server. Hence, Javascript relies heavily on
the user’s browser settings as the user can choose to enable or disable
it (Robbins, 2012, p. 459).
Javascript is a dynamic programming language, meaning that it
does not need to be passed through a compiler to translate the code to
another that the browser understands. Instead, the browser reads and
interprets the code directly.
Javascript is also loosely typed. This is particularly useful when
defining a variable. For example, if a variable is set to a value of 5,
that variable does not have to be specified programmatically since
Javascript automatically recognizes it.
Javascript allows programmers to script the presentation layer of
documents in web browsers and define behaviors to those documents
with event handlers. An event handler is a Javascript function that is
embedded inside the HTML tags and invoked by the browser when
certain events occur (Flanagan, 2011, p. 10). According to (Gotmare
& Jeure, 2008, p. (3:56)), there are two types of event handlers:
45
1. Interactive event handler: depends on the user interactivity
with the document. Some examples of this type are mouse
click (specified as onclick) and key press (specified as
onkeypress, onkeyup, and onkeydown).
2. Non-interactive event handler: does not need the user’s
interactivity. For example, the onload event handler executes
Javascript code when a form is loaded.
Javascript can be embedded anywhere in a document using
script element in one of two ways:
1. Embedded script: by inserting the code between the script
elements as shown in Figure 2.17.
Figure 0.17 Example of Embedded JavaScript
2. External scripts: by using the src attribute of the script
element to locate the script file (followed by a .js suffix) by
its URL containing the code as shown in Figure 2.18.
Figure 0.18 Example of External JavaScript
2.2.12
MySQL
Welling and Thomson (2008, p. 3) explained that MySQL “is a
very fast, robust, relational database management system (RDBMS)”.
MySQL is a multiuser, multithreaded server, meaning that its server
can be accessed by multiple users concurrently. MySQL is the world's
most popular open source database and has won the Linux Journal
Readers' Choice Award many times.
46
2.2.12.1 Advantages of MySQL
According to DuBois (2009, p. 3), there are several
advantages of using MySQL:
1. Speed: MySQL is fast.
2. Ease of use: MySQL is a high-performance but
relatively simple database system and is much less
complex to set up and administer than larger systems.
3. Query language support: MySQL uses SQL (Structured
Query Language), which is the standard language for
all modern database systems.
4. Capability: MySQL server is multithreaded, which
means that multiple users can connect and access
multiple databases simultaneously. In addition, MySQL
provides many interfaces depending on users' needs:
command-line, web browsers, and GUI and these
interfaces are available for many programming
languages.
5. Portability: MySQL runs on many popular operating
systems: Unix, Linux, Windows and NetWare.
Moreover, MySQL can be used on high-end servers or
even small personal computers.
6. Small size: Compared to other database systems,
MySQL has a relatively smaller distribution size.
7. Availability and cost: MySQL is an open source
database systems available under multiple licensing
terms. Under the terms of GNU General Public License
(GPL), MySQL is free for most in-house uses. MySQL
is also available with commercial licenses for
organizations. That do not want to be bound by the
conditions of the GPL.
47
2.2.13
XAMPP
According to its official web site, i.e. www.apachefriends.org,
XAMPP is an open-source web server package that can be installed on
Windows, Linux, and OS X. It is an acronym that stands for X
meaning cross-platform, A meaning Apache HTTP server, M meaning
MySQL, P meaning PHP, and P meaning Perl.
XAMPP acts as a server on local computer, allowing developers
and programmers to check their work without connection to the
internet. Hence, they can run their work locally before deploying these
pages to the real server.
XAMPP is a freeware and is licensed under GNU GPL.
2.2.14
TortoiseSVN
TortoiseSVN is “an open-source Windows shell extension that
provides Subversion support” (Berlin & Rooney, 2006, p. 166). In
other words, TortoiseSVN allows programmers to work with
Subversion from Windows Explorer. In addition, it provides user
interface for diffing, merging, and browsing via the Explorer.
Subversion is a version control system that manages files and
directories as well as their changes made over time. This enables
programmers to recover older versions of a particular files or
directories, or analyze the history of how the files or directories
changed. Furthermore, Subversion works across networks, allowing
people from different computers to work across the same files or
directories (Collins-Sussman, Fitzpatrick, & Pilato, 2008, pp. xi-xiv).
Figure 0.19 The Repository and Working Copies (Mason, 2006,
48
p.14)
Figure 2.19 shows the architecture of Subversion (Mason,
Pragmatic Version Control Using Subversion, 2005, p. 14). A
repository is the central location that contains the master copy of all
versions of the files inside a project. When Fred wants to work on this
project, he can start a mechanism called checking out. This
mechanism copies all of the files inside the project to his computer’s
local storage. The copied project in Fred’s computer is called working
copy. Wilma can also work on the same project by checking out to
obtain a working copy. When Wilma finished making changes to her
working copy and wants to save it to the repository, she can commit.
Her changes only affects the repository; it does not change Fred’s
working copy. Hence, Fred can update his working copy to receive
the latest files from the repository.
2.2.15
PHPMailer
PHPMailer is an open-source PHP class used to create and send
email. It is integrated by many popular open source projects such as
Wordpress, Drupal, and Yii.