Relational database mode
- Edgar Codd 1970
- The relational model represents how data is stored in Relational Databases.
- A relational database consists of a collection of tables, each of which is assigned a unique name.
- A relational database stores data in the form of relations (tables).
- Relational model can represent as a table with columns and rows.
- ROW - TUPLE
- COLUMN - **ATTRIBUTE
- Column: The column represents the set of values for a specific attribute.
- Attribute: Each column in a Table. Attributes are the properties which define a relation. e.g., Student’s Roll no, NAME, etc.
- A table has two properties rows and columns. Rows represent the records/tuples and columns represent attributes.
- Tuple : singe row, single record
- Relation Schema: A relation schema defines the structure of the relation and it represents the name of the relation with its attributes.
- e.g.; student (ROLL_NO, NAME, ADDRESS, PHONE, and AGE) is the relation schema for student.
- Degree: The total number of attributes which in the relation is called the degree of the relation.
- Cardinality: Total number of rows present in the Table.
14. Relation Instance: The set of tuples of a relation at a particular instance of time is called a relation instance. It can change whenever there is an insertion, deletion, or update in the database.
15. NULL values: The value which is not known or unavailable is called a NULL vale. It is represented by blank space.
- Relation Key: These are basically the keys that are used to identify the rows uniquely or also help in identifying tables. These are of the following types. Primary, foreign, candidate etc.
- DEGREE = 5 as 5 columns
- CARDIANALITY = 4 as 4 tuples/records