Database Concepts

Database System Concepts

• Data: Information stored in a structured form.
• Database: A structured collection of data stored electronically.
• Database Management System (DBMS): A software system used to manage databases and allows users to interact with data.
• Database Model: The way data is logically structured and represented such as relational, NoSQL, etc.
• Queries: A way to retrieve or manipulate data using languages like SQL.

Data Schema

A data schema defines the structure and organization of data within a database.

• Entity: A definable thing.
• Attribute: A property or characteristic of an entity.
• Relationship: How entities are associated with each other.
• Relation: A relation is a table with columns and rows.
• Tuple: A tuple is a row of a relation.
• Cardinality: The cardinality of a relation is the number of tuples it contains.

Characteristics of a Relation

1. Rows contain data about an entity.
2. Columns contain data about attributes of the entity.
3. Cells of the table hold a single value.
4. All entries in a column are of the same kind.
5. Each column has a unique name.
6. The order of the columns is unimportant.
7. The order of the rows is unimportant.
8. No two rows may be identical.

Entity Relationship (ER) Diagram

An ER diagram is a type of flowchart, illustrating how entities related to each other within a system.

Shapes

1. Rectangles represent entity sets.
2. Diamonds represent relationship sets.
3. Lines link attributes to entity sets and entity sets to relationship sets.
4. Ellipses represent attributes
   • Double ellipses represent multivalued attributes.
   • Dashed ellipses denote derived attributes.
5. Underline indicates primary key attributes

Example:

  flowchart TD
  customer["Customer"]
  id(["ID"])
  name(["Name"])
  street(["Street"])
  city(["City"])

  customer---id
  customer---name
  customer---street
  customer---city

  loan["Loan"]
  number(["Number"])
  amount(["Amount"])

  loan---number
  loan---amount

  borrower{"Borrower"}
  customer---borrower---loan