功能模塊6ES7 211-0AA22-0XB0操作便利
功能模塊6ES7 211-0AA22-0XB0操作便利
功能模塊6ES7 211-0AA22-0XB0操作便利
功能模塊6ES7 211-0AA22-0XB0操作便利

功能模塊獨(dú)立性是由內(nèi)聚性和耦合性?xún)蓚€(gè)定性指標(biāo)來(lái)度量的。內(nèi)聚性是度量一個(gè)功能模塊內(nèi)功能強(qiáng)度的一個(gè)相對(duì)指標(biāo)。耦合性則用來(lái)度量功能模塊之間的相互聯(lián)系的程度。

耦合

耦合是軟件結(jié)構(gòu)中各功能模塊之間相互連接的一種度量，耦合強(qiáng)弱取決于功能模塊間接口的復(fù)雜程度、進(jìn)入或訪問(wèn)一個(gè)功能模塊的點(diǎn)以及通過(guò)接口的數(shù)據(jù)。

耦合有以下幾種，他們之間的耦合度由高到低排列：

☆內(nèi)容耦合。如一個(gè)功能模塊直接訪問(wèn)另一個(gè)功能模塊的內(nèi)容，則這兩個(gè)功能模塊稱(chēng)為內(nèi)容耦合。

☆公共耦合。如一組功能模塊都訪問(wèn)統(tǒng)一全局?jǐn)?shù)據(jù)結(jié)構(gòu)，則稱(chēng)之為公共耦合。

☆外部耦合。如一組功能模塊都訪問(wèn)統(tǒng)一全局?jǐn)?shù)據(jù)項(xiàng)，則稱(chēng)之為外部耦合。

☆控制耦合。如一功能模塊明顯地把開(kāi)關(guān)量、名字等信息送入另一功能模塊，控制另一功能模塊的功能，則為控制耦合。

☆標(biāo)記耦合。如一組功能模塊共享了某個(gè)記錄，而不是簡(jiǎn)單變量，即這些功能模塊都需某一數(shù)據(jù)的子結(jié)構(gòu)時(shí)，就需要按該記錄的結(jié)構(gòu)進(jìn)行操作，并通過(guò)參數(shù)表來(lái)傳遞記錄信息，這樣的耦合稱(chēng)之為標(biāo)記耦合。

☆數(shù)據(jù)耦合。如一個(gè)功能模塊訪問(wèn)另一個(gè)功能模塊，被訪問(wèn)的功能模塊的輸入和輸出都是數(shù)據(jù)項(xiàng)參數(shù)，則這兩個(gè)功能模塊為數(shù)據(jù)耦合。

☆非直接耦合。若兩個(gè)功能模塊沒(méi)有直接關(guān)系，他們之間的聯(lián)系完全是通過(guò)主程序的控制和調(diào)用來(lái)實(shí)現(xiàn)的，便稱(chēng)這兩個(gè)功能模塊為非直接耦合，獨(dú)立性最強(qiáng)。

上面只是對(duì)耦合機(jī)制進(jìn)行了一個(gè)分類(lèi)。原則上講，功能模塊化設(shè)計(jì)總是希望功能模塊之間的耦合表現(xiàn)為非直接耦合方式。但是，由于問(wèn)題所固有的復(fù)雜性和空間方面的考慮，有時(shí)則要根據(jù)實(shí)際情況，全面權(quán)衡，選用其它類(lèi)型的耦合。 

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