精选优质文档-倾情为你奉上CH1 作业Fill in the blank.1、A data model is a notation for describing data or information. The description generally consists of three parts: 、 、 .2、 and is called the schema for that relation.3、When clearing key (keys), an attribute or list of attributes may be declared or . 4、If PRIMARY KEY is used, then attributes in S are not allowed to have as a value for their component
