Working on 1_WebApplicationDevelopment.md

1_WebApplicationDevelopment.md

@@ -21,8 +21,9 @@ Client-Server Model distributes processing btw:
 
 * Static web page: do not change for all requests.
   * Before HTML5, `.html/.htm` files are static web pages.
-* Dynamic web page: 
-  * 
+* Dynamic web page: can change its look everytime requested.
+  * some file extension related to dynamic web page e.g. `.php` (hypertext preprocessor), `.jsp` (java server page).
+  * Dynamic web pages are processed by both a *web server* and an *app server*, or *db server*
 
 ![Processing cycle of a static Web page](imgs/493603_1_En_1_Fig2_HTML.jpg)
 Processing cycle of a static Web page:
@@ -96,4 +97,15 @@ Events are things that happened
   * e.g. .NET Page class raises a **Load** event every time client reload web page.
 * Events can be static or non-static for different class.
 
-#### 1.4.5 Encapsulation
+#### 1.4.5 Encapsulation
+
+**Encapsulation** refers to two notions (concepts):
+* A class's properties & methods are bundle together and treated as a single unit
+* A class's properties & methods cannot be directly accessed by code outside of the class.
+
+Access restriction (enfored when declaring):
+* **private**: only accessed by code within the obj itself
+* **protected**: accessed by code within the obj itself and child class objs.
+* **public**: accessed by code in other class.
+
+