Bài giảng Web Technologies and e-Services - Bài 6: Web development models

Web Development Models • Web Application Architecture: client-server • Programming Languages on client side • Programming Languages on server side • 3-tier architecture and MVC model Content Client-Server Model Client side Server side Server Roles § Manage and store data, including: § User data § Application data § Provide processing services for data § Centralize data § Manage user authentication, authorization mechanisms via login function Client Roles § Provide user interface § Can store some small data (using cookie) § Can process data (check validity of data that are entered by users § Thin client: only provides user interface, centralize data processing on server side § Thick client: realizes data processing on client side § Can be accessed from everywhere with minimal software installation Client-Server Advantages §Centralized storage and processing. §No data redundancy §Enhance the ability of sharing data § If data are distributed on multi-systems of users, it will cause difficulties in sharing the data because each system has its own database architecture 3-Tier Architecture § Database Tier (Data Access Layer) § Stores and accesses data in low-level § Server Tier (Business Logic Layer) § Manages application connections and process data § Client Tier (Presentation Layer) § Provides interface and processing Business Logic Layer Data Access Layer Presentation Layer 3-Tier Architecture Advantages §Centralized Database can be accessed by many servers at the same time §Allow load balance of user connections on many application servers §Data Access Layer is consistently designed with hardware in order to serve specific its tasks: §Data manipulations: update, insert, remove, etc §Need more reliable hard drives §Business Logic Layer are designed to provide connection points for user connections and run multi-applications §Need more computing power of CPU Programming Languages Client Server Database Html Java, Ruby SQL JavaScript Visual Basic NoSQL Flash PHP, Perl Python Client Programming Language JavaScript §Event Handling §Statements (like C / Java) §Operators §Variables global (default) §Or local (e.g. var x = 1) §Types can change §Eg. x = 1; x = ‘Hello’ §Function definition (reuse) §Message Alerts §Page element access with Document Object Model §Views HTML page as a tree of elements Hello World Example • This provides an annoying popup – try it! <a href="" onMouseOver="(alert( 'Follow link to search on Google') )"> Search on Google Server Programming Language §Java – uses Java servlets, Java Server Pages (JSP) and Java Beans. §Ruby on Rails – uses ruby programs and Embedded Ruby (ERB). §Visual Basic – Uses VB programs and Active Server Pages (ASP). §Others: §PHP (Personal Home Page – originally) §CGI (Common Gateway Interface) §Perl (Named after the parable of the pearl) §Python (Named for the Monty Python skits) §Tcl (Tool Command Language) PHP • Very c-like • Classes, etc., work very much like C/C++ • Designed to work in the world of HTML • Is run-time interpreted by the web server Simple PHP Example Test page The time is now § PHP is meant to be invoked inline with content Page “escapes” into and out of a regular html document § File extension is .php (was .php3 for version 3) JSP Example Hello JSP Hello World: Produced MVC Development Model § Architectural Pattern from Smalltalk (1979) § Decouples data and presentation § Eases the development MVC – The Model § The “Model” contains the data § Has methods to access and possibly update it’s contents. § Often, it implements an interface which defines the allowed model interactions. § Implementing an interface enables models to be pulled out and replaced without programming changes. MVC – The View §The View provides a visual representation of the model. §There can be multiple views displaying the model at any one time. §For example, a companies finances over time could be represented as a table and a graph. §These are just two different views of the same data. §When the model is updated, all Views are informed and given a chance to update themselves. MVC – The Controller § It interprets mouse movement, clicks, keystrokes, etc § Communicates those activities to the model – eg: delete row, insert row, etc Example Control Flow in MVC § User interacts with the VIEW UI § CONTROLLER handles the user input (often a callback function attached to UI elements) § CONTROLLER updates the MODEL § VIEW uses MODEL to generate new UI § UI waits for user interaction MVC Advantages § MVC decouples the model, view, and controller from each other to increase flexibility and reuse. • You can attach multiple views to the model without rewriting it. • You can change the way a view responds to user input without changing the visual presentation. For example, you might use a pop-up menu instead of keyboard command keys. 3 Tier Layers vs. MVC •Presentation: • View is the user interface (e.g. button) • Controller is the code (e.g. callback for button) •Data: • Model is the database Database Presentation Summary § Client-Server Model § 3-Tier Architecture § Dynamic Web Programming Languages § MVC Model 25