Relational Model ↩

• Represents data as tables, made of rows and coloumns
• Each table is a relation, each row is a tuple, each coloumn is an attribute of the tuple.
• Primary Keys are unique identifiers for tuples in a relation.
• Foreign Keys establish relationship between tables.
• Benefits:
  • Data independance between storage and retrievals.
  • Data consistency regarding use of keys and relations.
  • Flexibility regarding modification of data and relationships.
  • Ease of Use regarding organizing and querying.

Integrity Constraints:

• Domain Constraints:
  • Atomic Values and null values
  • Unique tuples
• Key constraints:
  • Distinguish tuples, Unique
  • Super key - Set of 1 or more attributes that identiy tuples uniquely
  • Candidate key - Minimal super key (set -> 1 element)
  • Primary key - Candidate key chosen based on infrequent updates
  • Foreign key - Check consistency of data
  • General constraints - Avoid errors during modification

ER Model to Relational Model

• For converting an Entity set to a table:
  • Composite attributes -> New attributes in the table
  • Multivalued attributes -> Create a new table for the corresponding new relation
• When dealing with WEAK ENTITY set, convert Weak entity set to a table whose primary key is a combination of the primary key of the new table, and the primary key of the parent table. Make parent table. Add foreign key constraint in weak entity set table referencing primary key of parent table.
• For Relationships with Descriptive Attributes, create an INTERSECTION table with foreign keys referencing primary keys of the two entities and coloumns for the descriptive attributes.
• Remove redundant relations
• ER Model with Aggregation requires relation for aggregated relationship set. This is because multiple relations are required for the multiple associations between the superclass and the subclasses of data.
• That cannot be ommited.