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Non-prime attribute in DBMS?
Prime attribute are part of any candidate key. Non-prime attribute are not part of any candidate key.
What is key attribute and non key attributes?
A key attribute is an attribute that uniquely identifies a record in a database table. Non-key attributes are attributes that are not used to uniquely identify records, but provide additional information about the data.
foreign key?
when a primary key from one table is stored as an attribute of another table
Explain the concept of foreign key How a foreign key differs from a primary key?
Foreign keys are used to link one database with another. A primary key is an attribute of a record that allows users to identify information.
What conditions are required for 3NF violation to occur?
A relation violates third normal form (3NF) if it has a transitive dependency where a non-prime attribute depends on another non-prime attribute (which itself is not a candidate key). This means that a non-prime attribute is functionally dependent on another non-prime attribute rather than on a candidate key.
What are key attribute and non key attribute?
Attributes can be classified as identifiers or descriptors. Identifiers, more commonly called keys or key attributes uniquely identify an instance of an entity. If such an attribute doesn't exist naturally, a new attribute is defined for that purpose, for example an ID number or code. A descriptor describes a non-unique characteristic of an entity instance. An entity usually has an attribute whose values are distinct for each individual entity. This attribute uniquely identifies the individual entity. Such an attribute is called a key attribute. For example, in the Employee entity type, EmpNo is the key attribute since no two employees can have same employee number. Similarly, for Product entity type, ProdId is the key attribute. There may be a case when one single attribute is not sufficient to identify entities. Then a combination of attributes can solve this purpose. We can form a group of more than one attribute and use this combination as a key attribute. That is known as a composite key attribute. When identifying attributes of entities, identifying key attribute is very important.
What are the requirements for a relation to be in Second Normal Form?
A relation is in second normal form (2NF) if any of the following conditions apply: The primary key consists of only one attribute No non-primary key attribute exists in the relation Every non-primary key attribute is functionally dependent on the full set of primary key attributes
What is a non key attribute in normalization?
An attribute is another name for a field in a table. Some attributes are used as keys to help specifically identify individual records,like a code number or reference number for example. Most attributes are not used as keys. Any of those are non-key attributes.
What is difference between primary key and foreign key?
A primary key is an attribute (or combination of attributes) that uniquely identifies each row in a relation. A primary key is designated by underlining the attribute name. The primary key of an entity set allows us to distinguish among the various entities of the set. A foreign key is an attribute in a relation of database that serves as the primary key of another relation in the same database.
Explain two rules in relational model of database systems?
1) Entity Integrity: In a base relation, no attribute of a primary key can be null. 2) Referential Integrity: If foreign key exists in a relation, either foreign key value must match a candidate key value of some tuple in its home relation or foreign key value must be wholly null
Why do you use the concept of foreign key?
You use foreign keys to relate the information on one table to another. For example, Table one has customer information, name, address, user-id, etc and Table two has the orders that the customers request. Customer-id, item, number of items, cost per item, taxes, shipping address, etc.. You put in a foreign key on the orders table, so that the Customer-id is related to the User-id on the Customer table one. OK ?
What is the prime attribute in a database?
It is an attribute that does not occur in some candidate key.
