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The attribute (or combination of attributes) that is unique for every entity instance
e.g.: the account number of an account, the employee id of an employee etc.
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How would you define Entity and Attribute?
Entity is real world thing,person,place,event or object about which store data in database. Attribute are the characteristics of entity is called attribute.
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.
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 is the prime attribute in a database?
It is an attribute that does not occur in some candidate key.
Why is a Key important in a database?
a key is important in a database because using of that key only we can identify a unique attribute.
Each colunm in a database table represets a?
A column in a database represents an attribute to the entity that the table is representing. For example, "hair color" is an attribute if your entity is "customers of a hair salon". This would go in a column of the table (entity) titled "customers" in a management system of a hair salon.
What is a simple key in database?
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.
primary key?
attribute of an entity which uniquely identifies a specific instance of the data
1An attribute which can be used to uniquely identify the individual instances of the entity is?
Primery Key.
What is difference between object and entity?
A database object is represented as one of the following: database, schema, table, column, primary key, and foreign key A database Entity is: An entity is a thing or object of importance about which data must be captured. All things aren't entities - only those about which information should be captured. Information about an entity is captured in the form of attributes and/or relationships. If something is a candidate for being an entity and it has no attributes or relationships, it isn't an entity. Database entities appear in a data model as a box with a title. The title is the name of the entity.
How a developer of a relational database refers to a record?
A developer of a relational database refers to a single row of data as a "record." This record contains all the information related to a specific entity or object in the database.
How can you determine whether an object is an entity or an attribute?
Information contributed by Ramona Maxwell:An entity is a primary object in your database design and an attribute would further describe that object. In human terms if you are the entity, your attributes might be height, age, hair color and so on. In a sales database 'customer' might be an entity whose attributes could include name, address or account number. Entities and or their attributes are mapped in terms of their relationship to one another when designing your database. Helpful information on Entity Relationship Modeling can be found at the following link:http:/enzperiodzwikipediazperiodzorg/wiki/Entityzhyphenzrelationship_model
