Entity Relationship schemas include weak entity types, whose entities are identified by their inter-relationships to other entities. During the translation of the EER schema into a logical database schema, the weak entity types are either translated into logical units of the database (a relation or a class), or are embedded as attributes of other logical units. Formal studies of EER schemas either ignore the presence of weak entity types, or simplify their dependency structure. The presence of weak entity types in an EER schema may be problematic: A weak entity may not be easy to identify because it may be related to other weak entities in various ways, thus causing problems in schema comprehension, as well as in mapping it to a logical database schema.
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