Introduction to WebApps

Derek Bridge

Department of Computer Science,
University College Cork

Introduction to WebApps

Aims:

• to know the differences between desktop applications and webapps
• to see examples of web apps, including some software for the Sudbury Bird Sanctuary
• to know what is meant by thin and fat clients
• to know what is meant by two- and three-tier client-server architectures

Web sites vs. webapps

Web sites

make content (text, images, etc.) available

• allow user to navigate through the content
• often static web pages, but possibly dynamic

Web-based applications/ web applications/ webapps

enable user to achieve some task, e.g. search engine; e.g. online shop

• a more interactive experience
• dynamic web pages in response to user input

Desktop applications vs. webapps

• Desktop applications are installed on the user's PC/laptop
• Webapps are accessed through the user's browser
• E.g. Microsoft Outlook/Mozilla Thunderbird vs. Gmail/ Squirrelmail
• E.g. Microsoft Outlook's calendar/Apple iCal vs. Google Calendar
• E.g. Microsoft Streets and Trips vs. Google Maps
  Microsoft Streets and Trips screenshot; Google Maps screenshot

Desktop applications vs. webapps

Desktop applications exploit the PC/laptop system software and so typically:

• have rich and distinctive user interface
• have full system access, e.g. file storage and network connections
• store user data on the PC/laptop
• run faster
• require installation
• are platform-dependent
• even if Internet-enabled (which many now are), most of the processing is done on the PC/laptop; the server's role is limited (e.g. may just offer resources to download, opportunities to share/publish, a source for upgrades)

Desktop applications vs. webapps

Webapps are accessed through the user's browser and so typically:

• have a browser-based user interface, limited to what (X)HTML/CSS allows
• are denied system access
• store user data on the server (which has an up-side & a downside)
• often run slower
• require no special installation or set-up
• are platform-independent
• server has the major role

Presentational and application logic

(Note: not using the word 'logic' in the same way as in CS1105)

Presentational logic

The parts of an application that handle the user interface

Application logic (a.k.a. business logic)

The parts of an application that process the data, perform computations, etc.

Class exercise: Where is the presentational logic, and where is the application logic

• in a typical webapp?
• in a desktop application?
• in a typical Internet-enabled desktop application?

Thin and fat clients

In a client-server architecture, we can classify the client as follows:

Thin client

Little or no application logic takes place on a thin client

Fat client

All or most application logic takes places on a fat client

A narrower hardware definition: thin clients are very simple client computers (e.g. no hard disk), once called 'dumb terminals'.

Class discussion:

• If we connect a PC/laptop to the Internet, is it a thin or fat client?
• In a typical webapp, is the client thin or fat? What about a typical Internet-enabled desktop application?

Two- and three-tier client-server architectures

Two-tier client server architecture

The application is split over two participants:

• The client for presentation logic
• The server for application logic

Three-tier client server architecture

The application is split over three participants:

• The client for presentation logic
• An application server for application logic
• A database server (which may or may not be a different physcial computer from the application server) for data storage and data access

Three-tier client-server architectures

Sudbury Bird Sanctuary

A quick look at

• add_bird.php (add_sponsor.php is much the same)
• add_donation.php