1.1 關(guān)系術(shù)語
一個(gè)二維表就是一關(guān)系。常用的關(guān)系術(shù)語如下：
記錄：二維表中每一行稱一個(gè)記錄，或稱為一元組。
字段：二維表中每一列稱為一個(gè)字段，或稱為一個(gè)屬性。
域：即屬性的取值范圍。例如，在考試成績關(guān)系中，“數(shù)學(xué)”字段的域?yàn)?～100。在學(xué)生關(guān)系中，“性別”字段的域是“男”和“女”。
關(guān)鍵字：在一個(gè)關(guān)系中有這樣一個(gè)或幾個(gè)字段，它的值可以惟一地標(biāo)識(shí)一條記錄，稱之為關(guān)鍵字（Key）。
關(guān)系模式：對關(guān)系的描述稱為關(guān)系模式，其格式為：
關(guān)系名（屬性名1，屬性名2，…，屬性名n）
一個(gè)關(guān)系模式對應(yīng)關(guān)系的結(jié)構(gòu)，它的命名的屬性集合。
1.2數(shù)據(jù)獨(dú)立性
Relate to the technical term
A two the watch of be a relation. In common use relation technical term is as follows:
Record: Two form inside each lines call a record, or call a dollar set.
Word segment: Two form inside each rows call a word segment, or call a belongs to the sex.
Area:Belong to namely to take the worth scope sexually.For example, in examine score relation, the area of the " mathematics" word segment is 0 ～ 100.In student relate to, the area of the " sex" word segment is a " male" with the " woman".
Key word:There is like this a value for or a few words segment, it in a relation can only one marking a record, call it as the key word.( Key)
Relate to the mode:To relate to of describe to call to relate to the mode, its format is:
Relate to( belong to sex 1, belong to sex 2, … , belong to the sex a n)
A relation mode to the construction that should relate to, it assign name to of belong to the sex gather.
Data independent
Database system to 1:00 of the pass importance is application that database should independence in whichever in a specific way.The traditional data handles the application is a data related.The COBOL language procedure includes the detailed describing the data format to explain with record the elucidation with the document of the characteristic.
The customer is at the request of can change database constructio