Software Engineering, English, Swedish

redundancy, design diversity and protection against mistakes within the specification August 25, 2008

In an ideal world a system incorporating both redundancy and diverse design would provide good protection against both random component failure and some forms of design faults. It would not, however, provide protection against mistakes within the specification, as even diverse systems will generally be attempts to implement the same specification.

Research had shown that getting different teams to design a module does not remove the likelihood of similar faults in the implementations. The results showed that although the programs were each extremely reliable, they showed many common faults. Despite this finding, it is generally accepted that diverse design had great value in reducing common-mode failures, although it cannot guarantee freedom from such problems. Diverse design has also been shown to be of benefit in locating ambiguities within the specification, as different teams usually adopt diverse interpretations.

fault tolerence August 25, 2008

6.2 Types of faults

Nature

random faults:

The primary cause of random faults is hardware component failure. Statistical analysis may make it possible to estimate the likelihood of it failing within a given period of time.

systematic faults (design faults):

mistakes in the specification of the system; mistakes in the software; and mistakes in the  hardware design

   Duration

   permanent faults:

       This kind of faults remain in existence indefinitely, or untill some corrective action is taken, are termed permanent faults. Design faults, including software faults, are always permanent, as are many hardware components.

   transient faults

   This kind of faults can appear and then disappear after a short time.

   intermittent faults

   These faults, appear, disappear and then reappear at some later time.

Extent

   localized fault

      It may affect only a single hardware or software module

   global fault

       It has effects which permeate throughout the system

MVC pattern August 22, 2008

The Model-View-Controller (MVC) pattern separates the modeling of the domain, the presentation, and the actions based on user input into three separate classes [Burbeck92]:

Figure 1: MVC class structure 

Figure 2: Behavior of the passive model

Figure 3: Using Observer to decouple the model from the view in the active model

Figure 4: Behavior of the active model

執行TomCat August 21, 2008

新增環境變數:

variable name:  CATALINA_HOME

variable value: C:\apache-tomcat-6.0.18

命令提示字元視窗

(1) Start Up Tomcat

 C:\Documents and Settings\user>
 C:\Documents and Settings\user> C:\apache-tomcat-6.0.18\bin\startup.bat

(2) After startup, the default web applications included with Tomcat will be
    available by visiting:

       http://localhost:8080/

(3) Shut Down Tomcat
 C:\Documents and Settings\user>
 C:\Documents and Settings\user> C:\apache-tomcat-6.0.18\bin\shutdown.bat

詳細文件請看:C:\apache-tomcat-6.0.18\RUNNING.txt

設定環境變數 August 21, 2008

My computer右鍵->Properties->Advanced->Environment Variables

java August 21, 2008

JRE 是 JDK 的子集

皆為Java開發工作環境tool kits

array initializer August 14, 2008

• An array initializer can appear only in an array declaration.

        CORRECT!!

          int[ ] vec = {0,2,4,6}

        WRONG!!

          int[ ] vec;

          vec = {0,2,4,6};

• An array initializer can be an element of an array initializer. For example, the following:

          int[ ][ ] matrix = { {0 , 0 , 0 , 0} , {1 , 2 , 3} } ;

2D array August 14, 2008

matrix = new int [3][4];

compare ” == ” and ” equals “ August 13, 2008

String s1 = new String(“abc”);

String s2 = new String(“abc”);

s1==s2 returns false, while s1.equals(s2) returns true.

The variables s1 and s2 contain different reference values, denoting different objects. But as String, these objects are considered equal.