Database systems

Question 1

Conceptual Data Model

Answer 1

Detailed, technical data models no database-specific information

Question 2

Physical data model

Answer 2

Takes all constraints and properties of a relational database into account. Concrete structure can be created

Question 3

Identifyer

Answer 3

objects in relationships must be uniquely identified at all times

Question 4

Attributes

Answer 4

Concrete properties of entities are described as attributes. Each attribute has a name and a precisely-defined value range

Question 5

Entity

Answer 5

Something separate and distinct that can be uniquely identified among other similar entities.

Question 6

Subqueries

Answer 6

To formulate further SELECT statements within SELECT statements, Often used to formulate further conditions in the context of WHERE or Having. 
Schema:
MAIN QUERY
MAIN QUERY TABLE
filter condition WHERE
(Subquery
);

Question 7

ER-diagram

Answer 7

Used to display the all-important elements of a database structure. Only used to model database schemas. Elements: Entities, Attributes, Keys and Relationships

Question 8

Normalization

Answer 8

Optimizes the structure of a database and the normal form of a database is a measure of this structure

Question 9

Redundancy

Answer 9

The property of a dataset that describes that the deletion of data doesn’t necessarily result in a loss of information. For this, information must be saved more than once

Question 10

First normal form

Answer 10

Conditions to be fulfilled:

• All attributes must contain singe values. Composite values are not allowed
• Each individual data record uniquely identified with primary key

Question 11

Second normal form

Answer 11

Only relevant for tables with compound primary keys

• Criteria first normal form must be met
• Each non-key attribute is always dependent on the entire compound primary key and not just part of it

Question 12

Third Normal form

Answer 12

Criteria of the first normal form and in case of composite primary key, the second normal form must be fulfilled.
-Any non-key attribute depends directly on the key attributes that are not part of the Primary Key