The Relational Database Model

• Introduced by E. F. Codd in 1970, is based on predicate logic and set theory.


  Relational Model
• Is used extensively in mathematics to provide a framework in which an assertion (statement of fact) can be verified as either true or false.

  Predicate Logic
• A student with a student ID of 324452 is named Mark Reyes is an example of?

  Predicate Logic
• A part of mathematical science that deals with sets, or groups of things.

  Set Theory
• Used as the basis for data manipulation in the relational model.

  Set Theory
• Set A contains 15, 23, and 52 while Set B contains 41, 52, 70, 12 is an example of?

  Set Theory
• The relational model has three (3) components:

  1. A logical data structure represented by relations
  2. A set of integrity rules to enforce that the data is consistent and remains consistent over time
  3. A set of operations that defines how data is manipulated
• Is as a two-dimensional structure composed of rows and columns.

  Table (relation)
• Represents data about an entity.

  Each table row (tuple)
• Each table column represents an attribute, and each column has a distinct name.
• Each intersection of a row and column represents a single data value.
• All values in a column must conform to the same data format.
• Specific range of values.

  Attribute Domain
• Is an attribute or group of attributes that determines the values of other attributes.

  Key
• Invoice number is an example of a key.
• The value of one or more attributes determines the value of one or more other attributes.

  Functional dependence
• The attribute whose value determines another.

  Determinant
• The attribute whose value is determined by the other attribute.

  Dependent
• The standard notation for representing the relationship between attributes is: ATT_A → ATT_B.

  ATT_A is the determinant and ATT_B is the dependent.
• Involves a determinant that comprises multiple attributes. For example, STU_NUM → (STU_LNAME, STU_FNAME, STU_MI, STU_SECT)

  Functional Dependence
• A key that is composed of more than one attribute.

  Composite Key
• An attribute that is a part of a key.

  Key Attribute
• 5 Types of Keys

  1. Superkey
  2. Candidate Key
  3. Primary Key
  4. Foreign Key
  5. Secondary Key
• ATT_A → ATT_B is the Standard Notation.
• An attribute or combination of attributes that uniquely identifies any row in the table.

  Superkey
• A superkey without any unnecessary attributes.

  Candidate Key
• Cannot contain null entries.


  Primary Key
• A candidate key selected to uniquely identify all other attribute values in any given row.

  Primary Key
• Values must either match the primary key in another table or be null.

  Foreign Key
• Used strictly for data retrieval purposes.

  Secondary Key
• Is the condition in which each row in a table has its own unique identity.

  Entity Integrity
• Every reference to an entity instance by another entity instance is valid.

  Referential Integrity
• These are rules that are followed to maintain a good database design.

  Integrity Rules
• All primary key entries are unique.

  No part of a primary key may be null.


  Requirement (Entity Integrity)
• Each row will have a unique identity

  Foreign key values can properly reference primary key values.

  Purpose (Entity Integrity)
• No invoice can have a duplicate number, nor can it be null; in short, all invoices are uniquely identified by their invoice number.

  Example (Entity Integrity)
• • A foreign key may have either a null entry, as long as it is not a part of its table’s primary key, or an entry that matches the primary key value in a table to which it is related.
  • Every non-null foreign key value must reference an existing primary key value.

  Requirement (Referential Integrity)
• • It is possible for an attribute not to have a corresponding value, but it will be impossible to have an invalid entry.
  • The enforcement of the referential integrity rule makes it impossible to delete a row in one table whose primary key has mandatory matching foreign key values in another table.

  Purpose (Referential Integrity)
• A customer might not yet have an assigned sales representative (number), but it will be impossible to have an invalid sales representative (number).

  Example (Referential Integrity)
• Used to indicate the absence of some value.

  Flags