Relational Database Modeling

Question 1

Data Model

Answer 1

• notion for describing data or information
  1. Structure of the data
• data structures used to implement data in the computer are sometimes referred to as a physical data model, data models are somewhat higher level than data structures and are referred to as a conceptual model to emphasize the different in level
  2. Operations on the data: limited set of operations, or queries (retrieve information) and modifications (change the database)
  3. Constraints on the data: limitations on what the data can be (ex. day of the week is an int between 1 - 7)

Question 2

Important Data models for database systems

Answer 2

1. Relational model, including object-relational extensions
   - present in all commercial database management systems
2. Semistructured-data model, including XML and related standards
   - added feature of most relational DBMS

Question 3

Object-oriented features to relational models: Object-relational model

Answer 3

1. Values can have structure rather than being elementary types such as integer or strings
2. Relations can have associated methods

Question 4

Relational Model

Answer 4

• relational model gives us a single way to represent data as a 2D table called a relation

Question 5

Attributes

Answer 5

• columns of a relations
• appear at the tops of the columns
• describes the meaning of entries in the column below
• attributes in a relation schema are a set, not a list

Question 6

Schemas

Answer 6

• name of the relation and the set of attributes for a relation is called the schema for that relation
  (ex. Movies(title, year, length, genre)
• in a relational model, a database consists of one or more relations
• the set of schemas for the relations of a database is called a relational database schema, or database schema

Question 7

Tuples

Answer 7

• rows of a relation, other than the header row containing the attribute names are called tuples
• tuple has one component for each attribute of the relation
  (ex. (Gone With the Wind, 1939, 231, drama) is a tuple)
• must use the order in which the attributes were listed in the relation schema because the attributes are not present in a tuple

Question 8

Domains, or data type

Answer 8

• relational model requires that each component of each tuple be atomic; must be some elementary type such as an integer or string
• value cannot be a record structure, set, list, array or any other type that have its values broken into smaller components
• for each attribute of a relation is a domain of a particular elementary type
• components of any tuple of the relation must have a value that belongs to the domain of the corresponding column
  (ex Movies(title: string, year: integer, length: integer, genre: string)

Question 9

Equivalent Representations of a Relation

Answer 9

• relations are sets of tuples, not lists of tuples
• order in which the tuples of a relation are presented is does not matter
• we can reorder the attributes of the relation as we choose without changing the relation

Question 10

Relation Instances

Answer 10

• relationship about movies is not static and can change over time
• set of tuples for a given relation is called an instance of that relation
• a conventional database system maintains only one version of any relation, and this instance of the relation is called the current instance