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.
No. The attribute "prime" and "composite" applies only to integers.
A simple key consists of a single attribute to uniquely identify an entity occurrence, for example, a student number, which uniquely identifies a particular student. No two students would have the same student number.
Use Default and Not NULL
Strength is not an attribute of numbers.
database simple attritbute
Prime attribute are part of any candidate key. Non-prime attribute are not part of any candidate key.
a key to a different table
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
A non-key attribute is an attribute in a relation that is not part of the primary key. These attributes are functionally dependent on the primary key and are subject to normalization to reduce data redundancy and improve database consistency.
It is an attribute that does not occur in some candidate key.
transitive dependency
Transitive Dependency
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.
when a primary key from one table is stored as an attribute of another table
a key is important in a database because using of that key only we can identify a unique attribute.
Attribute is the property of entity.The composite attribute is like address(where street no,house no,town name all include).Composite key is also an attribute,but only which attribute are work as a unique identifier. Example:> In an ERD if vendor placed with orders then order(order day, order number) vendor(vendor code,vendor address) Here, order and vendor both are entity and order number, vendor code both are Composite key(because those are unique)but vendor address is a Composite attribute and order day(may be not unique)is an attribute only. So, we can conclude that all attribute not Composite key.
The difference is that partial dependency is when a database's attribute is only partially dependent on the primary key. Fully functional dependency is when the attribute is entirely dependent on the key.