#Database

What is Data?

• Data is a collection of raw, unorganized, unstructured facts and details
• Like text, observations, figures, symbols, and descriptions of things etc.
• Data doesn’t have any meaning unless processed.
• Types of Data
  • Quantitative
    • Numerical form
    • Weight, volume, cost of an item.
  • Qualitative
    • Descriptive, but not numerical
    • Name, gender, hair color of a person.

Data Model

• Provides a way to describe the design of a DB at logical level.
• Underlying the structure of the DB is the Data Model
  • A collection of conceptual tools for describing data, data relationships, data semantics & consistency constraints.
  • E.g: ER model, Relational Model, object-oriented model, object-relational data model etc.
• Collection of conceptual tools for describing data, data relationships, data semantics, and consistency

Relational Model

• Data relation represented in the form of table with columns and rows are called Relational Model
• Tuple
  • Each row is known as a tuple
• Columns
  • It represents the attributes of the relation
  • Each attribute, there is a permitted value, called domain of the attribute.
• Cardinality
  • Total number of tuples in a given relation.
• Degree of table
  • Number of attributes/columns in a given table/relation.

Normalisation

• Normalisation is a step towards DB optimisation
• Normalisation is used to minimise the redundancy from a relations.
• It is also used to eliminate undesirable characteristics like Insertion, Update, and Deletion Anomalies.
• Normalisation divides the composite attributes into individual attributes OR larger table into smaller and links them using relationships.

Transaction

• A unit of work done against the DB in a logical sequence.
• It is a logical unit of work that contains one or more SQL statements
• All these statements in a transaction either gets
  • Completed successfully (all the changes made to the database are permanent)
  • Or if at any point any failure happens it gets rollbacked (all the changes being done are undone.)
• Sequence is very important in transaction.