在软件的整个生命周期当中，软件维护占有大的一部分。基本上可以分成四个类别：
- 适应性维护：处理变更和适应环境变化
- 增强性维护：功能增强
- 矫正性维护：错误处理
- 预防性维护：提高可维护性，防止后续出现问题
有调查表明，有75%的维护时间花在一两种类别上，而有21%的时间花在错误修正的维护上。那么怎么样来提高软件的可维护性呢，以下是利于增强维护的几个方面：
维护因子(Maintenance Factors) 所占比重(PlusRange)
维护专家(Maintenance specialists) 35%
职员经难丰富(High staff experience) 34%
基于表格的变量和数据(Table-driven variables and data) 33%
基准代码低复杂度(Low complexity of base code) 32%
专业搜索引擎(Y2K and special search engines ) 30%
代码重构工具(Code restructuring tools ) 29%
再工程工具(Re-engineering tools ) 27%
高级语言(High level programming languages ) 25%
逆向工具(Reverse engineering tools) 23%
复杂分析工具(Complexity analysis tools) 20%
错误跟踪工具(Defect tracking tools) 20%
块更新(Y2K “mass update” specialists) 20%
自动化变更控制工具(Automated change control tools ) 18%
无偿加班(Unpaid overtime) 18%
质量度量(Quality measurements ) 16%
正式的基准代码检查(Formal base code inspections ) 15%
回归测试组件(Regression test libraries) 15%
优秀的响应时间(Excellent response time) 12%
大于10天的年度培训(Annual training of > 10 days ) 12%
较高的管理经验(High management experience ) 12%
自动化的帮助(HELP desk automation ) 12%
无错误的模块(No error prone modules ) 10%
在线错误报告(On-line defect reporting ) 10%
生产力度量(Productivity measurements) 8%
易用(Excellent ease of use) 7%
用户满意度(User satisfaction measurements ) 5%
高团队士气(High team morale ) 5%
----------------------------------------------------------------------------------------
合计(Sum) 503%
而不利于系统维护性的因素如下:
| Maintenance Factors | Minus Range |
|---|---|
| Error prone modules | -50% |
| Embedded variables and data | -45% |
| Staff inexperience | -40% |
| High code complexity | -30% |
| No Y2K of special search engines | -28% |
| Manual change control methods | -27% |
| Low level programming languages | -25% |
| No defect tracking tools | -24% |
| No Y2K “mass update” specialists | -22% |
| Poor ease of use | -18% |
| No quality measurements | -18% |
| No maintenance specialists | -18% |
| Poor response time | -16% |
| No code inspections | -15% |
| No regression test libraries | -15% |
| No help desk automation | -15% |
| No on-line defect reporting | -12% |
| Management inexperience | -15% |
| No code restructuring tools | -10% |
| No annual training | -10% |
| No reengineering tools | -10% |
| No reverse-engineering tools | -10% |
| No complexity analysis tools | -10% |
| No productivity measurements | -7% |
| Poor team morale | -6% |
| No user satisfaction measurements | -4% |
| No unpaid overtime | 0% |
| Sum | -500% |
原文见:
http://en.wikipedia.org/wiki/Software_maintenance