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A relation has:
Relational Schema:
A relational schema shows the relation's name, its attributes and the domain of every attribute. If R is the name of a relation and A1, A2...An is a list of attributes showing R then R (A1, A2...An) is known as a relational schema. Every attribute in this relational schema takes a value from some explicit domain called Domain (Ai).
For instance, the relational schema for relation PERSON as in Figure will be: PERSON (PERSON_ID:integer, NAME: string, AGE:integer, ADDRESS:string)
Total number of attributes in a relation indicates the degree of a relation. Hence the
PERSON relation includes four attributes, so this relation is of degree 4
What subschema expresses ? A subschema expresses the external view. (External schemas are called also called as subschemas)
What is the aim of logical schema ? The main motive of the logical schema is to ensure the portability of procedures and models on various physical schemas at runtime.
What is known as a search key? An attribute or set of attributes used to look up records in a file is known as a search key.
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it can be possible to create any table without primary key
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