软件的易维护性是指理解、改正、改进软件的难易程度。通常影响软件易维护性的因素有易理解性、易修改性和(7)。在软件的开发过程中往往采取各种措施来提高软件的易维护性。如采用(8)有助于提高软件的易理解性；(9)有助于提高软件的易修改性。在软件质量特性中，(10)是指在规定的一段时间和条件下，与软件维持其性能水平的能力有关的一组属性；(11)是指防止对程序及数据的非授权访问的能力。

(102)

(103)

(100)

(101)

Inside　the　computer,　the　operation　system(of　another　software　module　called　a　data　communication(71))must　decide　which　program　will　get　control　next.　Each　program　remember,　is　associated(72).　　a　particular　front　-end　port.　If　a　program's　data　have　not　yet　reached　its　front　-　end　buffer,　there　is　no　point　giving　that　program　control.　Thus　the　data　communication　monitor　sends　its　own(73)signal　to　the　front　-end　devices　next　port　is　polled.　Note　that　the(74)computer　speed.　The　computer　never　has　to　wait　for　a　terminal　or　a　communication　line.　Instead,　it　is　the　expressive　front　-　end　processor　that　waits　for　the　slower　system(75)to　respond.

(97)

(98)

(95)

(96)

Software　engineering　is　the　science　and　art　of　specifying,　designing,　implementing,　and(66)with　economy,　timeliness　and　elegance,　programs,(67)and　operating　procedures　whereby　computers　　can　be　made　useful　to　humanity.

This　definition　implicitly　sets(68)the　basic　goal　of　software　engineering　research　and　development:　　The　basic　goal　of　software　engineering　is　to　facilitate　specification,　design,　implementation　and　evolution　　of　programs,　documentation　and　operating(69)which　are　useful　to　humanity　in　an　economic,(70)and　elegant　manner(using　the　appropriate　science　and　art).