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COMP 2714 Relational Database Systems > Module 0 + 1 > Flashcards

Module 0 + 1 Flashcards

Introduction

1
Q

What is data?

A

Facts and statistics gathers for analysis, usually digitized.

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2
Q

What is information?

A

Data put into meaningful and useful context and given to the appropriate audience for them to use.

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3
Q

What is a information?

A

System that manages information.

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4
Q

What are the key building blocks of an information system?

A
  • Inputs
  • Processes
  • Outputs
  • Databases
  • Technology
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5
Q

What is a database?

A

An organized collection of related data.

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6
Q

What is a DBMS?

A

Database management system.

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7
Q

General functions of DBMS?

A
  • Defining a database (specifying types, structures, and constraints for the data)
  • Constructing a database (Storing the data on a medium)
  • Manipulating a database (Querying and updating the database)
  • Maintaining a database (Ensuring database efficiency, correctness and safety)
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8
Q

What are the components of a database system?

A
  • The stored database
  • The DBMS
  • The applications (to manipulate the data)
  • The users (people who use the DBMS to interact with the database)
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9
Q

What is conceptual database design?

A

Important phase in designing a database application.
Step 1: Universe of Discourse (UoD). Also known as the mini-world. It is the context in which the system will be.
Step 2: Converting UoD to a data model.

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10
Q

What is normalization?

A

Removing redundancies (removing duplicate data)

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11
Q

Why are redundancies bad?

A
  • Extra work
  • Waste of storage
  • Inconsistent data
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12
Q

What is a relational data model?

A

Visual representation of the relationship between collections of data.

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13
Q

What is data integrity maintenance?

A

The DBMS must define and enforce constraints on the data based on semantics (rules defined according to context).

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14
Q

What is query processing?

A

DBMS ability to run queries (questions about the data) and return data (answer said questions).

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15
Q

Is the DBMS capable of security management?

A

Yes

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16
Q

What are the three parts of Three-Schema Architecture?

A
  • External level
  • Conceptual level
  • Internal level
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17
Q

What is the external level responsible for (Three-Schema Architecture)

A

Provides access to particular parts of the database to users.

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18
Q

What is the conceptual level responsible for (Three-Schema Architecture)

A

Describes the structure of the whole database for a community of users.

19
Q

What is the internal level responsible for (Three-Schema Architecture)

A

Describes the physical storage structures of the database.

20
Q

What is data independence via the Three-Schema Architecture?

A

Ability to change the schema at one level without having to change the schema at the next higher level.

21
Q

Logical data vs physical data independence?

A

Logical: change conceptual without changing the eternal views.
Physical: change the hardware without changing logical schema.

22
Q

What is a entity-relationship (ER) model/diagram?

A

Graphical data modelling technique that represents relationships between main entities.

23
Q

What is a entity?

A

Object with physical or conceptual existence. Each entity has attributes (attributes are particular properties).

24
Q

What is entity type?

A

What the combination of name and attributes describe.

25
Q

What is the most important key constraint?

A

Keys must be unique.

26
Q

Composite vs simple attributes? Differences?

A

Composite attributes can be divided into smaller parts which represent simple attributes with independent meaning. E.g. name (composite attribute) can be divided into first, middle, and last name.

27
Q

Several attribute keys

A

Entity keys composed of multiple attributes. Combination of attributes that make the key must be unique since keys still need to be unique no matter their composition.

28
Q

Single vs multi-value attributes. How are they represented in a ERD?

A

Multi-value attributes are double ovals while singles are one oval.

29
Q

Stored vs derived attributes

A

When an attribute is derived from a related attribute. E.g. age can be derived from birth date. Represented with a dotted-line oval.

30
Q

What are value sets of attributes?

A

Specified range for a particular attribute. E.g. age can only be between x and y.

31
Q

What is an entity set?

A

Collection of entities of a particular entity type. E.g. set of employees.

32
Q

What is a relationship?

A

Association among two or more entities. Symbol used is diamond.

33
Q

What are descriptive attributes?

A

Attributes for the relationship. Relationships may also have key attributes.

34
Q

What are the 3 relationship degrees? How many entities involved with each?

A
  • Binary 2
  • Ternary 3
  • N-ary n
35
Q

What are entity roles?

A

Role (label) that a entity plays in a relationship instance. E.g. department and employee -> employer and worker.

36
Q

Recursive relationships?

A

Only one entity involved. E.g. employee in “manages” relationship. An employee can work for as well as manage another employee.

37
Q

Relationship set?

A

Collection of relationships of the same type. E.g. a bunch of different relationships representing what projects different employees are working on.

38
Q

Relationship contraints?

A

Limit the combination of entities that may participate.
- cardinality constraints (ratio of entities)
- participation constraints (total participation and partial participation)

39
Q

Existence dependency?

A

Existence of another entity depends on its relationship to another entity.
E.g. every employee must work for a department. (Total participation and represented using a double line)
E.g. not every employee is a manager. (Partial participation)

40
Q

Weak entities?

A

Do not have key attributes of their own. E.g. dependent of an employee.
They have partial keys (attribute of the owner entity) that have dotted underlines. Weak entities always have total participation. Relationship related to a weak entity must also have double lines and is called the IDENTIFYING RELATIONSHIP.

41
Q

Enhanced entity relationship (ERR) model?

A

Entity type is called class. Subclasses and superclass. Attributes of superclass are inherited. Represented with the U symbol (open side is towards the subclass). Subclasses can have their own unique attributes.

42
Q

Specialization vs generalization?

A

Specialization: deriving subclasses from a superclass.
Generalization: Abstracting similar entities into one superclass.

43
Q

EER constraints?

A

Total = double line
Partial = single line
Overlapping = circled o
Disjoint = circled d

COMP 2714 Relational Database Systems (3 decks)

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