Two technicians are discussing relays. Technician A says that relays can fail because the relay winding is open. Technician B sa
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Answer:
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Explanation:
Some of the Important Observation used in Entity Relational Diagram.
1. A Chemist can be involved one project or many projects
2. A project can hire just one or many chemists.
3. A chemist can lead over one or many projects
4. A project can have only one project leader chemist.
5. A project can be done in 1 or many laboratories.
6. A laboratory can host 0 or 1 projects.
7. A laboratory can have 1 or many equipments.
8. An Equipment can be in 1 or 0 laboratories.
9. A chemist can have 0 or many types of equipments.
10. An Equipment can have 0 or 1 chemist at a time
Notations:
PK=Primary Key:
A primary key, also called a primary keyword, is a key in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number
FK=Foreign Key:
A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them
Composite key:
A composite key is a combination of two or more columns in a table that can be used to uniquely identify each row in the table when the columns are combined uniqueness is guaranteed, but when it is taken individually it does not guarantee uniqueness
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