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Databases and Data Management > Theoretical Questions > Flashcards

Theoretical Questions Flashcards

1
Q

What is a database?

A

A database is a system that stores data and makes it possible for users to work with that data OR an organised collection of structured information or data, stored electronically

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2
Q

What was the first kind of database?

A

Navigational Database / Integrated Database Systems IDS

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3
Q

What is the query language for navigational databases?

A

CODASYL (Conference/Committee on Data System Languages)

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4
Q

What is the primary benefit of a navigational data base over reading data sequentially?

A

Allow to navigate directly from record to record following relations

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5
Q

Who invented relational databases?

A

Dr. Edgar Codd

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6
Q

What is the entity-relationship model used for?

A

To model data in database using relationships and to help navigating a database OR abstract logical model devoid of any implementation details OR physical models of relational databases

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7
Q

What are the three subcomponents of a relationship in data bases?

A

Entities, Attributes, and Relationships

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8
Q

How many cardinality types an entity-relationship can have?

A

4 (Zero or One, Exactly One, Zero or More, One or More)

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9
Q

What is the sign of an optional one (zero or one) cardinality type in crow’s foot notation?

A

ol

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10
Q

What is the sign of a mandatory (exactly one) cardinality type in crow’s foot notation?

A

||

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11
Q

What is the sign of a mandatory many (one or more) cardinality type in crow’s foot notation?

A

|{ or}|

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12
Q

What is the sign of an optional many (zero or more) cardinality type in crow’s foot notation?

A

o{ or }o

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13
Q

What is the data type for missing data in relational databases?

A

Null

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14
Q

What is the query language used for relational databases?

A

Structured Query Language (SQL)

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15
Q

What does DDL stand for?

A

Data Definition Language

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16
Q

What does DML stand for?

A

Data Manipulation Language

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17
Q

What does DCL stand for?

A

Data Control Language

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18
Q

How do you create a table in SQL?

A

create table a (a integer);

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19
Q

How do you read data from a table in SQL?

A

select * from a

20
Q

How do you add data to an SQL table?

A

Insert into a (a) values (1), (2);

21
Q

How do you delete data from an SQL table?

A

Delete from a where a = 1

22
Q

How do you modify data in an SQL table?

A

Update a set a=”new” where a=1

23
Q

How do you investigate what a query actually does in SQL?

A

Explain Query plan select * from a

24
Q

What is an attribute in SQL?

A

What’s referred to as a column and stores one single datapoint per entry in the database

25
Q

What is a tuple in SQL?

A

What’s referred to as a row in a table, individual entry in the database

26
Q

What is a primary key in SQL?

A

Primary key is a unique identifier with which an entry can be identified

27
Q

What is a composite key in SQL?

A

Combination of two or more primary keys and foreign keys in a joining table used to secure the uniqueness of entries into the joining table

28
Q

What is a candidate key in SQL?

A

Natural, Domain or business key. Candidate key is unique, might be primary and can be null, which is why it can’t be a primary key

29
Q

What are the two criteria of the first normal form?

A
  • Contains only atomic values

- There are no repeating groups

30
Q

How many join types does the ANSI SQL standard have?

A

5

  • Inner Join
  • Left Outer
  • Right Outer
  • Full Outer
  • Cross Join
31
Q

What does a cross join of two tables return in set theory terms?

A

A Cartesian Product

32
Q

What does an inner join of two tables return?

A

Returns the set of records that match in both tables

33
Q

What does a full outer join of two tables return?

A

Returns every record from all tables, if no matching record can be found to a record, it will be matched with a null value

34
Q

What concepts does a simple key-value store have to store data?

A

Keys and values

35
Q

What are the three concepts of a graph database?

A

Nodes, edges and properties

36
Q

What does OLTP stand for?

A

Online Transaction Processing

37
Q

What does OLAP stand for?

A

Online Analytical Processing

38
Q

What does ACID stand for?

A

Atomicity, Consistency, Isolation, Durability

39
Q

What are the two most popular data storage options?

A

Row oriented and Columnar oriented Data Storage

40
Q

What are the advantages of row-oriented data storage?

A
  • Easy to Insert a new row
  • Transactions are concerned about a single row
  • Row level security can be used with this design
41
Q

What are the disadvantages of row-oriented data storage?

A

Reading an entire row while only needing a single column

42
Q

What are the advantages if columnar-oriented data storage?

A
  • Reading a single column results in reading the minimum amount of data
  • Advanced techniques can be applied using the columnar approach
43
Q

What are the disadvantages if columnar-oriented data storage?

A
  • Hard to update

- Hard to insert into

44
Q

Which data storage is better suited for OLTP use cases?

A

Row Data Storage

45
Q

Which datas storage is better suited for OLAP use cases

A

Columnar Data Storage

46
Q

What do the letters in CAP theorem stand for?

A

Consistency, Availability, Partition Tolerance

47
Q

What does ETL stand for?

A

Extract, Transform, Load

Databases and Data Management (1 decks)

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