Task 2: ENTITY RELATIONSHIP

1. Data Modeling:
- Definition: The process of applying a most suitable organized and structured to data.
2. Flow:
- Conceptual Data Modeling.
- Logical Data Modeling.
- Physical Data Modeling.
- Data Model classified into three groups:
- Object-based.
- Record-based.
- Physical.
- Entity-Relationship (E-R) Model:
- Based on Object-based model, data can be perceived as object and relationship between them.
3. basic components:
- Entity.
-Relationship.
- Attributes.
- Entity Set.
- Relationship set.
4. Based on the association between one or more entities, relationship can be divided into 3 types:
- Self-relationships.
- Binary-relationships.
- Ternary relationships.
5. Based on mapping cardinalities, relationship divided into:
- One-to-One.
- One-to-Many.
- Many-to-One.
- Many-to-Many.
6. Some of others important elements of E-R:
- primary keys.
- Weak entity set.
- Strong entity set.
7. E-R Diagram: Attributes in E-R Model can be classified as:
- Multi-valued.
- Composite.
- Derived.
8. E-R Diagram construct step by step:
- Gather all the data that needs to be modeled.
- Identify data that can be modeled as real-world entities.
- Identify the attributes for each entity.
- Sort entity sets as weak or strong entity sets.
- Sort entity attributes as key attributes, multi-valued attributes, composite attributes, derived
 attributes, and so on.
- Identify the relations between the different entities.
9. Normalization:
- Definition: is the process of removing unwanted redundancy and dependencies.
- Initially, there are 3 normal forms:
- Denormalization: For customizing system for best performance, itӳ necessary to design the database possess minor redundancies.
 -Relational Operators:
-SELECT.
-PROJECT.
-PRODUCT.
-UNION.
-INTERSECT.
-DIFFERENCE.
-JOIN.
-DIVIDE.