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CS3101 > Week 1 Revision > Flashcards

Week 1 Revision Flashcards

1
Q

What were used before databases?

A

File systems, data stored in files, possibly separated with delimiters

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2
Q

What were some disadvantages of file processing systems?

A

<ul>
<li>Data redundancy and Inconsistency</li>
<li>Difficulty in accessing data</li>
<li>Integrity problems, hard to check constraints</li>
<li>Can't guarantee atomicity of updates</li>
<li>Can't deal with concurrent access by multiple users easily</li>
<li>Hard to provide user access to some but not all data</li>
</ul>

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3
Q

What is a database system?

A

A well controlled data repository with a collection of interrelated data and a set of programs to access the data

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4
Q

What does the data model cover?

A

The data, the data relationships, the data semantics (shape and structure) and the constraints on the data

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5
Q

What is described at the physical level of data abstraction?

A

How the record is stored

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6
Q

What is described at the logical level of data abstraction?

A

How the data and relationships between data is stored in the database

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7
Q

What is described at the view level of data abstraction?

A

Information about selected aspects of the data (certain groups)

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8
Q

What is an instance?

A

The actual content of the database at a particular point of time

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9
Q

What is physical data independence?

A

The ability to change the physical schema without affecting the logical schema

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10
Q

How should the interfaces between various levels be defined?

A

So that a change inone part does not seriously influence the other parts

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11
Q

What is logical data independence?

A

Ability to change the conceptual schema without having to modify the application programs which make use of them

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12
Q

What are some examples of alterations in the conceptual schema?

A

Additional or deletion of entities, attributes and relationships

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13
Q

Is logical data independence easier or harder to achieve than physical data independence?

A

Harder

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14
Q

What are the steps in the database design methodology?

A 
<ol>
  <li>Specification of requirements</li>
  <li>Choose data modelling style i.e. ER model</li>
  <li>Design data model</li>
<li>Choose database</li>
<li>Derive schema from data model</li>
<li>Populate database</li>
<li>Queries, updates, maintenance </li>
</ol>
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15
Q

Give an example of a data model

A

ER diagram

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16
Q

What are some benefits of using a data model?

A

<ul>
<li>Concise summary that you can present</li>
<li>Easy to understand</li>
<li>Hides irrelevant detail</li>
<li>Faster and easier to produce than code</li>
<li>Can go straight to code with some tools</li><li>
</li></ul>

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17
Q

What are the two database languages?

A

Data Definition Lanuage

Data Manipulation Language

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18
Q

Describe the Data Definition Language

A

DDL is the notation for defining the database scheme
Generates a set of table templates
Stores information about the data (metadata - integrity constraints, authorisation etc)
Commands such as CREATE, DROP, ALTER

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19
Q

Describe the Data Manipulation Language

A

Language for accessing and manipulating the data
Two types : procedural and declarative
Commands such as SELECT, INSERT, DELETE

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20
Q

What are the three functional components that a database system can be divided into?

A 
<ol>
  <li>Storage Manager</li>
  <li>Query Processor Component</li>
  <li>Transaction Component</li>
</ol>
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21
Q

What is the storage manager responsible for?

A

<ul>
<li>Interaction with the OS file manager</li>
<li>Efficient storing, retrieving and updating of data</li>
</ul>

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22
Q

What is the query processor component responsible for?

A 
<ul>
  <li>Interpreting and storing data definitions in the data dictionary</li>
  <li>Optimising queries</li>
  <li>Executing queries</li>
</ul>
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23
Q

What is the transaction management component responsible for?

A

<ul>
<li>Helping with atomicity</li>
<li>Ensuring database stays in a consistent state</li>
<li>Controlling interaction between concurrent transactions</li>
</ul>

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24
Q

What is the primary goal of a DBMS?

A

Store and retrieve database information that is both convenient and efficient?

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25
Q

What kind of collections of data are databases used to store?

A 
Ones that are
<ul>
  <li>Highly valuable</li>
  <li>Relatively large</li>
  <li>Accessed by multiple users and applications at the same time</li>
</ul>
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26
Q

What are the two main modes where databases are used?

A

<ul>
<li>Online transaction processing</li>
<li>Data analytics</li>
</ul>

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27
Q

What is the major purpose of a database model?

A

To provide users with an abstract view of the data

28
Q

What are the four data models?

A 
<ul>
  <li>Relational Model</li>
  <li>Entity Relationship Model</li>
  <li>Semi structured Data Model</li>
<li>Object based Data Model</li>
</ul>
29
Q

What are the three main phases of the design process?

A 
<ol>
 <li> Conceptual design phase </li>
 <li> Logical design </li>
 <li> Physical design </li>
</ol>
30
Q

What are the two things a database can be modelled as?

A

A collection of entities and the RELATIONSHIP between those entities

31
Q

What is an entity?

A

An object that exists and is distinguishable from other objects

32
Q

What are attributes?

A

Descriptive properties/characteristics of the object

33
Q

What is an entity set?

A

Set of entities of the same type that share the same set of attributes

34
Q

What are the five types of attributes?

A 
<ul>
<li>Simple </li>
<li>Composite</li>
<li>Single-valued</li>
<li>Multi-valued</li>
<li>Derived</li>
</ul>
35
Q

What is a simple attribute?

A

An attribute that is made up of a single component part

36
Q

What is a composite attribute?

A

An attribute that is made up of multiple component parts e.g. address

37
Q

What is a single valued attribute?

A

An attribute that can only have one value per entity

38
Q

What is an example of a single valued attribute?

A

Date of birth, salary

39
Q

What is a multi valued attribute?

A

An attribute that can have more than one value per entity

40
Q

What is an example of a multi valued attribute?

A

Phone number

41
Q

What is a derived attribute?

A

An attribute that is computed from other attributes

42
Q

What is an example of a derived attribute?

A

Age from date of birth and current date

43
Q

What is a relationship?

A

An association that exists between entities that is uniquely identifiable

44
Q

What is a relationship set?

A

Set of relationships between one or more entity sets

45
Q

What are the two cardinalities of relationship sets?

A

Binary relationships

N-ary relationships

46
Q

What do multiplicity constraints cover?

A

Number of times an entity can or must take part in a particular type of relationship

47
Q

Describe Participation

A

The MINIMUM number of times an entity must take part in the relationship set

48
Q

Describe Cardinality

A

The MAXIMUM number of times an entity can take part in a relationship set

49
Q

What is total participation?

A

An entity MUST take part in the relationship set

50
Q

What is partial participation?

A

An entity may or may not take part in the relationship set

51
Q

What is the cardinality of a one to one relationship?

A

1

52
Q

What is the cardinality of the left set in a one to many relationship?

A

Greater than 1

53
Q

What is a candidate key?

A

The minimal set of attributes that are needed to uniquely identify each entity

54
Q

What is a primary key?

A

The candidate key chosen to uniquely identify each entity

55
Q

What is a weak entity set?

A

An entity set with no candidate keys

56
Q

What do weak entity sets depend on?

A

The existence of an identifying entity set

57
Q

What are the conditions for relationships between weak entity sets and identifying entity sets?

A

<ul>
<li>WES must have total participation in relationship with identifying set</li>
<li>Must be one to many relationship from identifying set to weak entity set</li>
</ul>

58
Q

What is the discriminator of a weak entity set?

A

Set of attributes that distinguishes it among all entities of a weak entity set

59
Q

What is the primary key of a weak entity set formed by?

A

The primary key of the identifying entity set and the weak entity set’s discriminator

60
Q

What key concept is not formally represented in an ER diagram?

A

Foreign Keys

61
Q

How are composite attributes represented in an ER diagram?

A

Identation

62
Q

How are derived attributes represented in an ER diagram?

A

Parentheses

63
Q

How are multi-valued attributes represented in an ER diagram?

A

Braces

64
Q

How is total participation represented in an ER diagram?

A

Double line

65
Q

How is a cardinality of one represented in an ER diagram?

A

Arrow

66
Q

How are discriminators represented in an ER diagram?

A

Dashed line underline

67
Q

How are relationships to identifying entity sets represented in an ER diagram?

A

Double outline

CS3101 (13 decks)

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