abstract entities meaning in English

抽象本质
抽象存在

Characters are abstract entities that can be represented using many different character schemes or code pages
字符是可使用多种不同字符方案或代码页来表示的抽象实体。
Based on analyzing and abstracting entities and their relationships of rmro , e - r graph illustrating the main contents of rmro is proposed
本文首先分析了制造资源优化配置中的实体和关系，建立了其总体的实体一关系模型。