Lecture 6 Flashcards Preview

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Flashcards in Lecture 6 Deck (26):
1

Data

Raw facts and figures without any deeper meaning

2

Information

Data shaped into meaningful form through context

3

Knowledge

Results from experience and education

4

What does a relational database do?

It organises data into one or more related tables

5

What does a unique key do?

It identifies each row, and can be used to link different tables.

6

Data redundancy

unnecessary repetiiton

7

Why should redundancy be reduced? (2)

1. it increases the amount of storage required
2. It is a major source of data inconsistencies

8

What is one benefit of redundancy?

It can improve database performance since there is not needs for joint operations

9

What does database normalization do?

It manages the tradeoff between redundancy and performance (ease of use)

10

Requirements for 1NF?

1. The domain of each attribute contains only atomic values
2. The values of each attribute contain only one value from that domain

11

Requirement for 2NF?

1. Must satisfy 1NF
2. In the case of a composite key, there are no partial dependencies. ie. non-key attributes are dependent on all key attributes and not just a subset

12

Requirement for 3NF?

1. Must satisfy 2NF
2. There should be no transitive dependencies. Attributes should not be functionally dependent on other non-key attributes.

13

What is Entity relationship modelling (ERM)?

describes the relationship between entities (things of interest)

14

Entity relationship diagrams are built on what four elemental concepts?

1. Entities
2. Attributes
3. Relationships
4. Cardinalities

15

What are entities?

They are things of interest to an organisation

16

What are attributes?

They describe the entity on question

17

What are relationships?

They express that entities are linked together

18

What are cardinalities?

They represent the number of occurrences within one entity that are associated with occurrences in another.

19

What are the 3 types of cardinalities?

1. One-to-one: exactly one occurrence in entity A is associated with exactly one occurrence in entity B
2. One-to-many: Exactly one occurrence in entity A is associated with many occurrences in entity B
3. Many-to-many: Many occurrences in entity A are associated with many occurrences in entity B

20

What is optionality (lower cardinality) and upper cardinality?

The minimum amount of occurrences, and the maximum amount of occurences

21

What is an entity set and a relationship set?

It contains all entities of a similar kind / all relationships of a similar kind.

22

What are candidate keys and a primary key?

There are often multiple possible keys, and the one post suited as the main reference is the primary key. The primary key is chosen from all candidate keys

23

3 steps or constructing a data model and what do they entail?

1. Conceptual model: Identity all entities and relationships
2. Logical model: Identify the attributes of all entities and determine keys
3. Physical model: a database structure than can be implemented of a specific platform. All M:N relationships can been resolved through associative tables and normalisation has occurred.

24

SQL: Data definition language (DDL) meaning?

creating, deleting, and altering, databases and tables (STRUCTURE). Important when working with ERD.

25

SQL: Data manipulation language (DML) meaning?

retrieving, inserting, changing, deleting tuples/records (CONTENT)

26

SQL: Data control language (DCL) meaning?

user and permission management (ACCESS)