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Lernmaterialien für Database an der Frankfurt University of Applied Sciences

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TESTE DEIN WISSEN

What are redundancies? Which consequences are involved with redundancies?

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TESTE DEIN WISSEN

A redundancy is the multiple existence of value.
Consequences: Data can be changed and be found difficultly

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TESTE DEIN WISSEN

Please compare two database models and write two dis-/advantages for each of them.

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TESTE DEIN WISSEN

Hierarchic database model - disadvantages 
No flexibility concerning changes in structure
Storage have to be reserved for pointers
Relation database - advantages
Very flexible at changes in structure
No pointers needed, because information are inserted at the end of the table

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TESTE DEIN WISSEN

Review: Object databases

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TESTE DEIN WISSEN

- Resulting from the object oriented programming
- Data is regarded here as objects and is saved as such
- Manipulation of data takes place by means of method

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TESTE DEIN WISSEN

Review: Hierarchic database

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TESTE DEIN WISSEN

- Database is saved in separate, sequential files
- First column indicates the hierarchy level
- Highest hierarchy have to be released usefully

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TESTE DEIN WISSEN

Which important dis- and advantages do NULL values have?

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TESTE DEIN WISSEN

- Missing information while entering the date

- Special treatment in queries for NULL values necessary

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TESTE DEIN WISSEN

A database is divided in three levels.
Name and explain them.

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TESTE DEIN WISSEN

Intern level - this means only a physical storage
Extern level - Describes the different views of the end user on the data
Conceptual level - Set of rules for both other levels. Define for example tables and relations

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TESTE DEIN WISSEN

We have the quantities M1 := {Opel, Fiat, Audi, Audi}, M2 := {A2, Punkto, Zafira}
Name the Cartesian products.

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TESTE DEIN WISSEN

{(Opel, A2), (Opel, Punto), (Opel, Zafira), (Fiat, A2), usw...)}

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TESTE DEIN WISSEN

Which consequences do the three levels have for our relational database system?

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TESTE DEIN WISSEN

The intern level is not relational, because the kind of storage is defined as well as for other database models.
The extern level can but does not have to be relational. It depends on the view on the data within the language of programming.
The conceptual level works with the table and is strict relational.

Lösung ausblenden
TESTE DEIN WISSEN

We have the quantities M1 := {Opel, Fiat, Audi, Audi}, M2 := {A2, Punkto, Zafira} 


Name a subset of the cartesian product and their tuples.

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TESTE DEIN WISSEN

R1 := {(a, b) € M1 x M2 | a has model b in its sortiment}


(Opel, Zafira), (Fiat, Punto), (Audi, A2)

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TESTE DEIN WISSEN

In which level do you find the data language and why?

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TESTE DEIN WISSEN

The data language appears in the extern level.
It can't appear in the intern level because the level only considers the physically storage.
In the conceptual level rules are established, so no data language is needed here.

Lösung ausblenden
TESTE DEIN WISSEN

Give two differences between relations and tables.
Discuss its consequence.

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TESTE DEIN WISSEN

- Every element can occur once in a relation

- No NULL values can occur in a relation

- The order is strictly defined within cross products, not within tables

- Infinity of relations

- Sorting options within tables

Lösung ausblenden
TESTE DEIN WISSEN

Please give at least three requirements to a database we demand and explain it in your own words!

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TESTE DEIN WISSEN

Persistant save (The data should be saved persistent on the computer. Therefore, I will find the data after a computer new start or an unintentional breakdown of the system)
Free of redundancies (Redundancies act like poison for a database, because they lead to a lot of problems)
Administration functions (To be able to perform query operators on data, create tables and/or delete them)

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Q:

What are redundancies? Which consequences are involved with redundancies?

A:

A redundancy is the multiple existence of value.
Consequences: Data can be changed and be found difficultly

Q:

Please compare two database models and write two dis-/advantages for each of them.

A:

Hierarchic database model - disadvantages 
No flexibility concerning changes in structure
Storage have to be reserved for pointers
Relation database - advantages
Very flexible at changes in structure
No pointers needed, because information are inserted at the end of the table

Q:

Review: Object databases

A:

- Resulting from the object oriented programming
- Data is regarded here as objects and is saved as such
- Manipulation of data takes place by means of method

Q:

Review: Hierarchic database

A:

- Database is saved in separate, sequential files
- First column indicates the hierarchy level
- Highest hierarchy have to be released usefully

Q:

Which important dis- and advantages do NULL values have?

A:

- Missing information while entering the date

- Special treatment in queries for NULL values necessary

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Q:

A database is divided in three levels.
Name and explain them.

A:

Intern level - this means only a physical storage
Extern level - Describes the different views of the end user on the data
Conceptual level - Set of rules for both other levels. Define for example tables and relations

Q:

We have the quantities M1 := {Opel, Fiat, Audi, Audi}, M2 := {A2, Punkto, Zafira}
Name the Cartesian products.

A:

{(Opel, A2), (Opel, Punto), (Opel, Zafira), (Fiat, A2), usw...)}

Q:

Which consequences do the three levels have for our relational database system?

A:

The intern level is not relational, because the kind of storage is defined as well as for other database models.
The extern level can but does not have to be relational. It depends on the view on the data within the language of programming.
The conceptual level works with the table and is strict relational.

Q:

We have the quantities M1 := {Opel, Fiat, Audi, Audi}, M2 := {A2, Punkto, Zafira} 


Name a subset of the cartesian product and their tuples.

A:

R1 := {(a, b) € M1 x M2 | a has model b in its sortiment}


(Opel, Zafira), (Fiat, Punto), (Audi, A2)

Q:

In which level do you find the data language and why?

A:

The data language appears in the extern level.
It can't appear in the intern level because the level only considers the physically storage.
In the conceptual level rules are established, so no data language is needed here.

Q:

Give two differences between relations and tables.
Discuss its consequence.

A:

- Every element can occur once in a relation

- No NULL values can occur in a relation

- The order is strictly defined within cross products, not within tables

- Infinity of relations

- Sorting options within tables

Q:

Please give at least three requirements to a database we demand and explain it in your own words!

A:

Persistant save (The data should be saved persistent on the computer. Therefore, I will find the data after a computer new start or an unintentional breakdown of the system)
Free of redundancies (Redundancies act like poison for a database, because they lead to a lot of problems)
Administration functions (To be able to perform query operators on data, create tables and/or delete them)

Database

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