元模型相对容易理解；它们与实体关系模型非常相似。
Metamodels are relatively easy to understand; they are similar to an entity-relationship model.
数据模型很快就会变得非常庞大，包含很多实体和关系。
Data models quickly become very large with many entities and relationships.
此模型描述系统中的实体及其关系。
It describes the entities in the system and their relationship.
此模型描述系统中的实体及其关系。
It describes the entities in the system and their relationship.
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