Cubes at ETHZ - ETH Zurich | Flashcards & Summaries

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# Lernmaterialien für Cubes an der ETHZ - ETH Zurich

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What is ROLAP?

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It's a Relational way to represent a cube (OLAP). OLAP used to be cubes in the 70s but now it's not so clear anymore.

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What is the 3rd Normal Form?

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Additionally to the 2nd normal form we also want no transitive dependency. So if dependency is A <- B <- C then A and C should not be in the same table and the table should be split up into (A, B) and (B, C)

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What is the 1st Normal Form?

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It is that we forbid that a table is nested. That means to make it to 1st Normal Form we will split up an entry with multiple values into multiple entries with one value each.

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What's a cube?

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A cube is a list of dimensions indexing a list of measures

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What is OLAP?

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Online Analytical Processing. When we produce reports from aggregated vast quantities of data. So it's about reading a lot.

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What is a data warehouse and what are its 4 properties?

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Its a collection of data that is made for the management's decision-making process. The data is:

1. subject-oriented
2. integrated
3. time-variant
4. nonvolatile

The data warehouse is where the data is put before it is aggregated for the final representation.

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What does MDX stand for? What is it?

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Multi-Dimensional Expressions.

It is a querying language for cubes.

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What does slicing in the cube translate to in the facts table? (in terms of relational algebra)

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A selection (where clause in SQL)

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What are some properties of OLTP?

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• Lots of transactions on small portions of data.
• Consistent and Reliable Record-Keeping
• Normalized Data
• fully interactive

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What would you use OLAP for?

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• Web analytics
• Sales analytics
• Management support
• Statistical analysis (census)
• Scientific databases (e.g., bio-informatics)

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What is the 2nd Normal Form?

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It is that we forbid a table to depend on only part of the key. It must depend on the whole key. To make it to 2nd Normal Form we have to split a table into two tables such that in the resulting tables all columns are dependent on their keys - they can still also be dependent on another column in the table unlike 3NF

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What' slicing? What's dicing?

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Slicing: pick one specific value (e.g. where brand = "Samsung")

Dicing: look at all values (e.g. group by year)

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Q:

What is ROLAP?

A:

It's a Relational way to represent a cube (OLAP). OLAP used to be cubes in the 70s but now it's not so clear anymore.

Q:

What is the 3rd Normal Form?

A:

Additionally to the 2nd normal form we also want no transitive dependency. So if dependency is A <- B <- C then A and C should not be in the same table and the table should be split up into (A, B) and (B, C)

Q:

What is the 1st Normal Form?

A:

It is that we forbid that a table is nested. That means to make it to 1st Normal Form we will split up an entry with multiple values into multiple entries with one value each.

Q:

What's a cube?

A:

A cube is a list of dimensions indexing a list of measures

Q:

What is OLAP?

A:

Online Analytical Processing. When we produce reports from aggregated vast quantities of data. So it's about reading a lot.

Q:

What is a data warehouse and what are its 4 properties?

A:

Its a collection of data that is made for the management's decision-making process. The data is:

1. subject-oriented
2. integrated
3. time-variant
4. nonvolatile

The data warehouse is where the data is put before it is aggregated for the final representation.

Q:

What does MDX stand for? What is it?

A:

Multi-Dimensional Expressions.

It is a querying language for cubes.

Q:

What does slicing in the cube translate to in the facts table? (in terms of relational algebra)

A:

A selection (where clause in SQL)

Q:

What are some properties of OLTP?

A:
• Lots of transactions on small portions of data.
• Consistent and Reliable Record-Keeping
• Normalized Data
• fully interactive

Q:

What would you use OLAP for?

A:
• Web analytics
• Sales analytics
• Management support
• Statistical analysis (census)
• Scientific databases (e.g., bio-informatics)

Q:

What is the 2nd Normal Form?

A:

It is that we forbid a table to depend on only part of the key. It must depend on the whole key. To make it to 2nd Normal Form we have to split a table into two tables such that in the resulting tables all columns are dependent on their keys - they can still also be dependent on another column in the table unlike 3NF

Q:

What' slicing? What's dicing?

A:

Slicing: pick one specific value (e.g. where brand = "Samsung")

Dicing: look at all values (e.g. group by year)

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