Keys

• Key is one of the important concepts of database A key is defined as the column or set of columns in a table that is used to identify either row of data in a table or establish relationship with another table.
• If a table has id, name and address as the column names then each one is known as the key for that table. The keys are also used to uniquely identify each record in the database table.
•  Primary Key It is a set of one or more attributes that can uniquely identify tuples (rows) within the relation. The primary key should be chosen in such a way, i.e. its value must not be changed. There should not be duplicate in the record of primary key. Primary key can be atomic or composite. The field chosen as primary key, cannot accept null value.

In the Question:

In files, there is a key associated with each record which is used to differentiate among different records. For every file, there is at least one set of keys that is unique. Such a key is called.

The Answer is Primary key.A database table must have a primary key for Optim to insert, update, restore, or delete data from a database table.

Hence the Option D is Correct.

Relational Database

Database: A database is information that is set up for easy access, management and updating.

In a relational database, data is stored in different tables with relationships to each other.. The database has rows and columns and a unique key for each data point.These tables communicate and share information, which facilitates data search ability, organization and reporting.

In the case of relational database, a Relational Database Management System (RDBMS) performs these tasks. An important feature of this database system is that a single database can be spread across several tables.  E.g. Base, Oracle, DB2, SyBase, Informix, etc.

Terms Related to Database

Various terms related to relational database are as follows

1. Relation It is a table with columns and rows which represent the data items and relationships among them. It has three important properties a name, cardinality and a degree.

These properties help us to further define and describe relations.

(i) Name The first property of a relation is its name, which is represented by the tide or the entity identifier.

(ii) Cardinality The second property of a relation is its cardinality, which refers to the number of tuples (rows) in a relation.

(ii) Degree The third property of a relation is its degree, which refers to the number of attributes (columns) in each tuple.

2. Domain It is a collection of all possible values from which the values for a given column or an attribute is drawn. A domain is said to be atomic if elements are considered to be indivisible units.

3. Attributes The heading columns of a table are known as attributes. Each attribute of a table has a distinct name.

4. Tuples The rows in a relation are also known as tuples. Each row or tuple has a set of permitted values for each attribute.

In the Question:

In the relational modes, cardinality is termed as 

The Answer is Number of tuples.A table row contained in a table in the tablespace is known as a tuple.

Hence the Option A is Correct.

Relational Database

Database: A database is information that is set up for easy access, management and updating.

In a relational database, data is stored in different tables with relationships to each other.. The database has rows and columns and a unique key for each data point.These tables communicate and share information, which facilitates data search ability, organization and reporting.

In the case of relational database, a Relational Database Management System (RDBMS) performs these tasks. An important feature of this database system is that a single database can be spread across several tables.  E.g. Base, Oracle, DB2, SyBase, Informix, etc.

In the Question:

A database that contains tables linked by common fields is called a

The Answer is relational database.In DBMS, the data is stored as a file, whereas in RDBMS, data is stored in the form of tables.

Hence the Option C is Correct.