phpWebApp article

The phpWebApp Framework and the
SEE-GRID Resources Web Application

Dashamir Hoxha1 and Elda Nallbani1

Institute for Informatics and Applied Mathematics (INIMA)
Lek Dukagjini, 3
Tirana, Albania
{dhoxha,enal}@inima.al
http://www.inima.al/

Abstract. This paper presents the phpWebApp framework, which is
a framework based on PHP, used to facilitate the construction of web
applications. It explains its features and advantages over other methods
of building web applications, and then makes an overview of its main
components. It also presents a concrete web application which is built
using this framework. . . .

1 Introduction

The SEE-GRID resources map1 is a dynamic web page which provides informa-
tion about the grid resources of each country participating in the SEE-GRID
project. This information is stored in a database and is displayed dynamically
in a weather-map. The information in the database needs to be updated period-
ically by the GRID administrators of each country and cluster.
In order to enable the administrators to access this database easily and to
modify the relevant information, we built a web application which acts as web
interface to this database. This application, to which we will refer to as gridrc
(SEE-GRID Resources), allows every participant of SEE-GRID to see all the
information about SEE-GRID resources, and allows only the administrators to
modify the information about the cluster/country that they administrate. All
this is done from a user-friendly web interface.
The tool that we used to build gridrc is the phpWebApp framework. This
framework is based on PHP and allows the web application developer to work at
a higher level than PHP, making the development of the web application easier.
It is template based and works like an engine that ﬁlls the templates of the
application with data that are retrieved from the database or that are computed
by the PHP code. It then generates (creates) an HTML page, which is sent to
the browser by the web server.

1
http://see-grid.inima.al/see-grid-weather/

2 Dashamir Hoxha et al.

2 SEE-GRID Resources (gridrc) Web Application

This web application displays the grid resources for the countries that partici-
pate in the SEE-GRID project 2 . For each country it displays the list of clusters
that are available in this country. For each cluster it displays derails such as ad-
ministrator contacts (name, email, phone), security contacts, summary resources
(total number of nodes, type of cluster, storage type, etc.), grid applications that
are installed, and a list of nodes with details for each node. It also displays some
summary tables (reports) about clusters and applications, which are generated
by processing the data in the database.
Besides displaying these data, the web application has also an edit mode 3
which allows the authorized persons (admins of the countries and clusters) to
modify the data in the database. When the application is in edit mode, there
will be an Edit button at the pages that can be modified. However, it will ask
for a password before allowing any modifications. The idea is that each country
has an admin and each cluster has an admin, and only the admins can modify
the data. Who is considered to be admin? Whoever knows the edit password
(there is a different password for each country and each cluster).
The admin of the country can add/delete clusters, can set/reset the password
of the cluster admins, can modify some general info about the cluster, and of
course can change his own password. The admin of the cluster can modify the
details of the cluster, can change the cluster admin password (his password),
etc. After the country admin logins, he can change his own password and can
change/set/reset the password of the cluster admins.
Once the database of the resources is filled with data, the SEE-GRID re-
sources map can read these data, and using a javascript library (overLIB), can
produce the map. overLIB is a JavaScript library created to enhance websites
with small popup information boxes (like tooltips) to help visitors around a web-
site. It can be used to provide the user with information about what will happen
when they click on a link as well as during the movement of the mouse.
We are going to talk first about the phpWebApp framework, and then we
will illustrate its features with examples by the gridrc web application.

3 Why We Didn’t Use Plain PHP?

Constructing a web application with PHP or any similar scripting language is
usually much more difficult than constructing a desktop application (e.g. using
VB, VC++, KDevelopper, etc.). It is because it has inherently some bad sides
and weak points which can be observed in most of the web applications. Some
of these problems and difficulties are discussed below.

2
http://see-grid.inima.al/gridrc/
3
http://see-grid.inima.al/gridrc/edit.php

phpWebApp and SEE-GRID Resources 3

3.1 Mixing HTML, CSS, JavaScript, PHP, SQL codes
Suppose that we have constructed a web application with PHP. If we inspect
the code inside one of the files of the application, what we usually see is HTML
code, JavaScript code, CSS code, PHP code, SQL code etc. all jammed together.
This kind of mixing many languages inside the same file is a really bad thing,
for these reasons:

It makes the editing of the application very difficult. Most of the editors
have code colorizing features, automatic indentation features, etc. for many
languages, in order to simplify editing and to make it easy. But when they
are faced with such a mix of languages, very often they get confused. As a
result, such features become useless, and even they become harmful, because
they may colorize wrongly or indent wrongly.
It makes the maintenance of the application very difficult. It is very dif-
ficult for somebody else to try to read, to understand and to modify such
a code, and even for the author of the code himself (after some time has
passed).
Makes difficult the team work. Suppose that a web application is constructed
by a team that is composed of PHP programmers, who construct the server
side logic of the application, web designers (HTML+CSS) who create the
look and feel of the application, JavaScript programmers who construct the
client side logic of the application, and DB specialists who construct the
database and the queries. In this case it is very difficult for any one of them
to make modifications in a big file that has lots of unfamiliar code to them,
without making any mistake. Take for example the web designer, it is very
difficult for him to change the look and layout of a web page that is tightly
interwoven with PHP code.
Increases the complexity of web applications. Different from the previous
example, suppose now that a web application is constructed by one or more
programmers and each of them is responsible for a certain part of the ap-
plication. In this case each of them has to have good skills in all of them:
PHP, HTML, CSS, JavaScript, database, etc. This is difficult to be achieved
and it increases the complexity and the difficulties of constructing a web
application.

It is clear that such a mix of codes is a bad thing and a bad practice and it
must be avoided as much as possible.
The HTML syntax offers a possibility to take out the JavaScript code and
the CSS code in separate files. It is like this:

<script language="javascript" src="file.js"></script>
<link rel="stylesheet" href="file.css" type="text/css" />

However there is no standard way to clearly separate the HTML, PHP and
SQL codes. You can try to keep the degree of mixing of HTML and PHP code
at a minimum level by carefully designing the application. E.g. you can place all


the PHP code unrelated to the HTML generation (the code that contains the
logic of the application) in a separate file and keep the file that generates the
HTML page as lean as possible.
A better solution to separate the HTML and PHP codes is to use a template
engine. It uses templates for generating the final HTML page. Each template is a
pure HTML file, which also has some slots or variables in it. The values of these
variables are calculated by the PHP code and they are passed to the engine.
Then the engine reads the templates, replaces the variables by their values and
thus generates an HTML page which is sent to the browser.

3.2 From one page to the next, global variables are lost.

Different from the desktop applications, web applications are discrete. This
means that one view (page) of the application has almost no connection to
the next one. This is because global variables are lost and each page has to be
constructed from the scratch.
Each web application can be thought as a state machine. Each time you see in
the browser the application at a certain state. When you click something inside
the page, then the application goes to another state and it sends to the browser
another page. However, oddly, web applications cannot keep their state in their
global variables because from one request of the browser to the other they are
lost. This is inherent in all web applications because the HTTP protocol is a
stateless protocol [2].
Usually, web applications try to overcome this problem by using session vari-
ables, cookies, parameters in the CGI query, etc. However there is no easy and
standard way and this often results in overhead (because you have to write spe-
cial code for storing and retrieving these variables), increased complexity, etc.

3.3 Lack of modularity.

Big web applications are usually huge and monolithic, not only in code but also
in the programing logic. So they have all the problems that are caused by the lack
of modularity: they have high complexity, it is difficult to maintain or improve
them, the code cannot be reused easily in other applications, etc.
By careful design and implementation, a web application can be made more
modular, and usually big web applications do it (otherwise it would be too
difficult to build and maintain them). However this modularization is different
from one application to the other, it is specific to the web application itself and
cannot be reused or applied to another web application, because it is not enough
general4 .
4
If it is somehow general, so that it can be applied for a certain domain of web
applications, then it would be a framework or engine, and the application would not
be considered to be built on plain PHP.


4 Why Not Another Framework?

From the above section it is clear that using a framework or engine or template
system is usually better than using plain PHP, for building a web application. To
make a comparison with desktop applications, you can build a windows applica-
tion even using the C Win32 API, but it is much more easy and convenient to use
VB or VC++ (which are in fact just frameworks, based on C API, for building
windows applications). To build a windows application using the C API would
be just like using Assembly for writing a program. Similarly, using a framework
for building a web application usually is more convenient then using plain PHP.
Of course it has some overhead, because you will have to learn how to use the
framework first, before starting to build the application.
There are a lot of frameworks or template systems that can be used for
building a web application. Just make a search at sourceforge.net5 for “web
application framework” or for “template system” and you will discover a lot of
them. Some of them are ColdFusion6 , Smarty7 , etc.
However we chose phpWebApp because:

– It is free (licensed with GNU GPL).
– In our opinion, it is more flexible, powerful, user-friendly and better than
the others.
– We have experience with it and know it better than the others.

5 The PHP Web Application Framework (phpWebApp)

5.1 What is phpWebApp

phpWebApp is an application framework for building PHP web applications
based on relational databases. It separates the graphical design and layout of
the application from the logic of the application by using templates. It also pro-
vides a kind of event-based programing model (similar to that used in Visual
Basic and other visual languages), object-oriented structure of the application,
easy interface to database, code re-usability, etc. It can be used to construct eas-
ily and efficiently eCommerce applications, eGovernment applications, eContent
applications and any kind of web applications.

5.2 phpWebApp Features

Some of the features of the phpWebApp framework, and the advantages and
benefits of using it for building web applications, are these:
5
http://sourceforge.net/search/?type=soft
6
http://www.macromedia.com/software/coldfusion/
7
http://smarty.php.net/


– The framework uses a kind of template system which separates the layout
from the logic of the application, so a graphical designer can easily improve
the layout of the application without getting messed with the logic and with-
out having to understand it. It makes easier the work of both the graphical
designer and the programmer. The framework also separates the JavaScript
code and the CSS code from the HTML code and the DB queries from the
PHP code.
– The framework gives the possibility to divide a page into several parts which
can be used in other pages as well. This makes the user interface of the
application (the layout, the graphical part) more structured and easier to
understand and maintain and makes easier the work of the graphical de-
signer.
– For the framework, a web application is like a state machine, which can be
represented and described by one or more state chart diagrams. Each page
of the application that is displayed represents the application in a certain
state. Clicking to a link causes a transition to another state of the application.
The state of the application is kept in the so-called state variables, which are
similar to session variables. This simpliﬁes the design and the implementation
of web applications.
– The framework supports an event-based programming model. When a tran-
sition from one state of the application to another happens, it may trigger
an event as well, which is handled by a function (event handler). It is imple-
mented by building on top of CGI another level of communication between
browser and server. The event-based programming model makes the logic of
the application easy to build, understand and maintain, and makes easy the
work of the web programmer.
– The framework gives to the web programmers the possibility to create web
components (called WebBox-es). They have their own user interface (HTML+CSS
code), client side behavior (JavaScript code), server side behavior (PHP
code), state variables, events, event handlers, etc. Each component can be
made almost 100% self contained and independent from the other parts of the
application, and it can be a state machine on its own.The big state machine
of the application is a composition of the state machines of its components.
This can reduce dramatically the complexity of a web application; instead of
having to build a huge monolithic state machine for the whole application,
we can build several small state sub-machines and compose them.
– Since the components are independent from the rest of the application, they
can be very easily reused in other web applications. So, the framework pro-
vides code re-usability, which means that if you have constructed something
once, you don’t have to re-construct it again when you need it another time,
but reuse the existing one.
– The framework brings closer the client-side and the server-side logic of a web
application. E.g. the state variables are available and can be accessed both
on the client side (JS code) and on the server side (PHP code).
– The framework simpliﬁes the interaction of the application with the database.
It also makes it almost database independent. This means that in case that


you decide to change the database on which your application is based (e.g.
switching from MySQL to Oracle), then the application itself doesn’t need
to be changed at all, it will work all the same.
– An application based on the framework is easy to maintain (debug, improve,
extend, etc.). So, the framework also facilitates an iterative and incremental
development approach for web application projects.
– The framework supports internationalization (i18n) and localization (l10n),
based on standard GNU gettext tools. This means that a web application
can be translated easily in other languages.
– Another thing is that phpwebapp offers good debugging features, which
makes easier the development. Without debugging, software development
would be a nightmare, isn’t it.

6 The phpWebApp Components

6.1 Templates

Templates are normal XHTML files which can contain some additional tags and
some variables. These tags and variables are processed by the framework and are
replaced with XHTML code when the web page is created. These templates allow
the web page designer to work almost independently from the database designer
and from the PHP programmer that implements the logic of the application.
Some of the extra tags that can be used in templates are:

Include : It is used to include a template inside another template. It provides
modularity (breaking a large page into smaller templates)

<include src="{{./}}edit/cluster_edit.html" />

Repeat : This element is connected with a recordset by the attribute ”rs”. Its
body is processed for each row of the recordset. Before processing the content
for a certain row, all the fields of the recordset are declared as variables with
values taken from the current record.

<table>
<repeat rs="clusters">
<tr><td>{{cluster_name}}</td></tr>
</repeat>
</table>

If : The content of this element is processed conditionally: if the value of the
attribute “condition” is true, then it is processed, otherwise it is not pro-
cessed. The value of the condition is calculated as a PHP expression (after
the template variables have been replaced).

<if condition="!{{admin}}">
<a class="button" href="javascript:edit()">Edit</a>
</if>

Recordset : Each recordset has a unique id.
<recordset id="country">
<query>
SELECT country_name, description FROM countries
WHERE country_id = ’{{country->id}}’
</query>
</recordset>

Some other elements that can be used are:
<var>, <webbox>, , etc.

6.2 Template Variables
Variables are used in templates to insert a dynamic string in it. Its value is not
known at the time that the template is designed, it is given by the php part
of the application or by the framework (e.g. by getting it from the DB or by
calculating it according to a certain logic). Their value is always a string, which
replaces the variable when the template is processed by the framework.
Template variables are denoted like this: {{var_name}}. var name inside
the curly braces may contain any character, and it is case sensitive. Double
curly braces is chosen because single curly braces sometimes may occur inside a
template, e.g. in JavaScript code.
A template variable is declared in the php code of the application, in the
php code of the weboxes, in the <var> template tag, in the <repeat> template
element (implicitly), or gets its value from a state variable, from a global php
variable or from a php constant that has the same name as the {{variable}}.
In the php code, the variables are declared using these functions:
WebApp::addVar(var_name, var_value);
WebApp::addVars(assoc_array);
The framework ﬁnds the value of a {{variable}} like this:
1. First the current scope is searched for it.
2. If it is not found, then the scope above it is searched, and so on until it is
found.
3. If it is not found in any scope, then session variables are searched for it.
4. If it not found among session variables, then global variables of PHP are
searched for it.
5. If it is not found there, then constants of PHP are searched.
6. If it still is not found then its name is taken as its value (e.g. {{var1}} is
replaced by {var1}).


6.3 State Variables
State (session) variables are persistent variables (don’t loose their value from
one page to another. They can belong to webbox-es or they can be global to the
application. They correspond to the global variables of the desktop applications
(e.g. VB applications).
The framework keeps the state variables inside the web-page itself. They are
passed from PHP (server) to HTML (client) and from HTML to PHP continu-
ously. If you view the source of a page of an application, you will notice them
in the end; they are appended automatically to the end of each page by the
framework itself. Also, whenever you make a transition to another page of the
application, using the function GoTo(), all the state variables are sent to the
server as well, and this is taken care by the function GoTo() itself.

6.4 Transitions
A transition is the move of the application from one state to another (usually
from one page to another). A state of the application is composed of a template
ﬁle and some state variables. A transition is usually triggered by a client-side
event in the browser, such as: clicking a link, pressing a button, submitting a
form, timeout of a javascript timer, etc.
In phpWebApp a transition is done by calling the function GoTo() which
is declared by the framework itself, e.g. GoTo(’page1.html’). In this case, the
GoTo() function sends a request to the web-server for another page. This request
is processed by the framework, which loads the template ’page1.html’ processes
it and sends it to the browser.

6.5 Events
Usually, during a transition, an event is sent as well to the next page. This
event is handled by the PHP code of the application, which may do some input
validation, save data to database or get data from database, change the state of
the application, etc.
An event can be sent to a webbox using this function (which calls GoTo() to
make a transition):
SendEvent(’targetBox’, ’eventName’, ’arg1=val1;arg2=val2’);
When the framework gets an event, it sends it to the webbox targetBox by calling
the function targetBox::on_eventName($event_args$). The variable that is
passed to this function is an associative array which contains the arguments of
the event.

6.6 WebBox-es
A WebBox is a template which has also some PHP code associated with it. It is
a self-contained and independent template which can be easily included in other

pages or in other applications. In fact, it may also have some JavaScript code,
CSS stylesheets, SQL queries etc., associated with it.
It is denoted by the tag <WebBox> and it has an ID attribute:

<webbox id="box_id">

</webbox>

The identifier must be different for each WebBox used in the application.
The PHP code (as well as JS code, CSS styles etc.) are associated to the
WebBox by means of box id, the identifier of the WebBox. When the framework
parses a <WebBox> tag, it looks for a file named box id.php in the same folder
where the WebBox template is. If it finds such a file, it includes it.
The box id.php file must contain the definition of a PHP class that extends
the class WebObject, like this:

<?php
class box_id extends WebObject
{
. . .
}
?>

The class WebObject is defined by the framework. It contains the member func-
tions WebObject::init(), WebObject::onParse() and WebObject::onRender().
The function onRender() of the class WebObject is called by the frame-
work at the time of the HTML page construction (the page that is sent to the
browser), just before the template of the WebBox is output-ed (rendered). Ac-
tually WebObject::onRender() is an abstract (empty) function, and the frame-
work expects the class box id to override it, in order to do something useful for
the WebBox. What is usually done in box_id::onRender() is assigning values
to the variables used in the template of the WebBox box id, so that the template
is rendered properly.
Besides the file that contains the template of the WebBox and the box id.php
that contains its PHP class, there may be other files as well that belong to the
WebBox. These are: box id.js that contains the JavaScript code of the WebBox,
box id.css that contains the stylesheet of the WebBox, box id.db that contains
the recordsets of the WebBox, etc. If the framework finds such files, it automat-
ically integrates them in the generated HTML page. For example, it includes
box id.js and box id.css in the head of the page. Of these files, the template is
the most important. There can be a WebBox without JS code or without PHP
code, but there cannot be a WebBox without template code.

6.7 Database

The database component of the application is very important, because most of
the web applications are based on relational databases. It allows an application


to interact with a database, to get and display data from it, to save, update
and delete data in it, etc. The framework tries to make this interaction as easy
and as convenient as possible for the application developer, without loosing the
flexibility. It also tries to ensure that the database is used in an abstract way,
so that it doesn’t matter for the programmers whether the database is MySQL,
Oracle, etc.
To enable the DB component, open the file ’config/const.Settings.php’ and
set the constant ’USES DB’ as ’true’. After this, create the file ’config/const.DB.php’
and define in it the constants DBHOST, DBUSER, DBPASS and DBNAME,
which will be used to open a connection with the database.
Inside a template, we can get and display data directly from the DB using
the tags <Recordset> and <Repeat>.

6.8 WebClass-es and WebObject-s

The element <WebClass> defines a web class, but it by itself does not produce
any HTML output. The element <WebObject> declares an object of the class
and the content (the template) of the <WebClass> is used for this object. These
two elements can be used for small components which can be used more than
once in an application (WebBox-es are not suitable for this, because their ID
must be unique in the application).
Some of the WebClass-es that are defined by the framework are these:

tabs : displays a horizontal tab-like menu.
datebox : can be used to select the date from a popup calendar.
listbox : can be used to display a list of values which are taken from a recordset.
dbTable : can be used to display and edit the content of a database table.
formWebObj : makes easy the handling of big forms (which have many inputs).

7 The Structure of GRIDRC

Since gridrc is based on phpWebApp, it follows some conventions that are re-
quired by the framework. It has the files ’index.php’ and ’webapp.php’ which
are the same for all the phpWebApp-based applications. These files include the
framework classes, which then read the configuration and the templates of the
application and create an HTML page which is sent to the browser.
The configuration of the application is required by the framework to be in
the folder ’config/’ and it has these files, which define some constants:

const.Options.php : constants that modify the behavior of the framework.
const.Paths.php : constants about the paths of the application.
const.Debug.php : constants that enable/disable debugging features.
const.DB.php : constants about the database connection.

The templates and webbox-es of the application are placed in the folder
’templates/’. They are organized so that there is one folder for each webbox and


the included webbox-es are placed in sub-folders of this folder. Each webbox has
an HTML file (which is required), and it usually has also a PHP class. It may
also have a JavaScript file (.js) and a CSS file (.css), which are included by the
framework at the head of the page. If it interacts with the database, it can also
have a .db file that contains the queries.

8 Future Work

The future work includes improvement of the documentation of the framework:
writing a manual for the developers and tutorials for getting them started. It
includes also improvements that can be done to the framework itself. In general
these are small improvements and they will be done as the need for them arises
(when the applications that use the framework need them).
Another thing that can be done is to improve the tools for working with the
framework. E.g. an Emacs mode can be created that helps when working with
the framework. Or maybe a plug-in can be developed for Quanta for building
phpWebApp applications. We may try as well to do automatic code generation
of web applications from UML models (e.g. from UML state chart diagrams,
since each webbox is like a state machine), and reverse engineering (building
automatically a UML model from an existing application).
Another useful thing that can be done in the future is to build reusable
WebBox-es or WebObject-s, which can facilitate the construction of new appli-
cations. These reusable components/objects can be even organized in a higher
level framework (based on phpWebApp) for building web applications of a certain
kind.

References
1. The phpWebApp documentation: http://phpwebapp.sourceforge.net/
2. Roy T. Fielding and Richard N. Taylor. “Principled design of the modern Web
architecture”. ACM Transactions on Internet Technology (TOIT), 2(2), May
2002, pp. 115-150. This document is available at http://www.ics.uci.edu/ field-
ing/pubs/webarch icse2000.pdf.

phpWebApp article

Recommended

More Related Content

What's hot (20)

Viewers also liked (8)

Similar to phpWebApp article (20)

More from Dashamir Hoxha (20)

phpWebApp article