Data Warehousing and OLAP Questions and Answers

Q: For constructing Data warehouse from operational databases, which of the following operations are necessary ?

The necessary operations are Extract and Load.A data warehouse is built from operational databases by the ETL process: data is extracted from the source systems, cleaned and transformed into a consistent form, and loaded into the warehouse, usually in periodic batches.Create and Edit and Query and Update are operations on operational (OLTP) data, not steps in building a warehouse. Slice and dice are OLAP operations used to analyse the warehouse once it exists.

Q: Which of the following statement(s) is/are true ?(i) Dimension tables of star schema models are brought to normalized form to reduce redundancy.(ii) Snowflake structure can reduce the effectiveness of browsing since more joins are needed for query.

Only statement (ii) is true, so the answer is (ii) only.In a star schema the dimension tables are deliberately kept denormalised: each dimension is one wide table joined directly to the fact table, trading some redundancy for simple, fast queries. Normalising the dimension tables into sub-tables is exactly what turns a star schema into a snowflake schema, so statement (i) is false as a description of the star model.Statement (ii) is true: because a snowflake splits each dimension into several tables, a query must make more joins, which reduces the effectiveness of browsing the dimensions.

Q: The data contained in the data warehouse is described by :

Data warehouse contents are described by metadata.Metadata is data about data. In a warehouse it records where each item came from, how it was transformed and loaded, its structure and meaning, and how it is summarised, so users and tools can find and interpret the data.Operational data is the source data from day-to-day systems, relational data is a storage model, and 'active data' is not a descriptive layer; none describes the warehouse contents.

For constructing Data warehouse from operational databases, which of the following operations are necessary ?

A.Extract and Load
B.Create and Edit
C.Query and Update
D.Slice and Dice

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: A

The necessary operations are Extract and Load.

A data warehouse is built from operational databases by the ETL process: data is extracted from the source systems, cleaned and transformed into a consistent form, and loaded into the warehouse, usually in periodic batches.

Create and Edit and Query and Update are operations on operational (OLTP) data, not steps in building a warehouse. Slice and dice are OLAP operations used to analyse the warehouse once it exists.

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Which of the following statement(s) is/are true ?

(i) Dimension tables of star schema models are brought to normalized form to reduce redundancy.
(ii) Snowflake structure can reduce the effectiveness of browsing since more joins are needed for query.

A.(i) only
B.(ii) only
C.(i) and (ii)
D.None of the above

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

Only statement (ii) is true, so the answer is (ii) only.

In a star schema the dimension tables are deliberately kept denormalised: each dimension is one wide table joined directly to the fact table, trading some redundancy for simple, fast queries. Normalising the dimension tables into sub-tables is exactly what turns a star schema into a snowflake schema, so statement (i) is false as a description of the star model.

Statement (ii) is true: because a snowflake splits each dimension into several tables, a query must make more joins, which reduces the effectiveness of browsing the dimensions.

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The data contained in the data warehouse is described by :

A.Relational data
B.Meta data
C.Operational data
D.Active data

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

Data warehouse contents are described by metadata.

Metadata is data about data. In a warehouse it records where each item came from, how it was transformed and loaded, its structure and meaning, and how it is summarised, so users and tools can find and interpret the data.

Operational data is the source data from day-to-day systems, relational data is a storage model, and 'active data' is not a descriptive layer; none describes the warehouse contents.

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Match the following :

(i) OLAP	(a) Regression
(ii) OLTP	(b) Data Warehouse
(iii) Decision Tree	(c) RDBMS
(iv) Neural Network	(d) Classification

(i) (ii) (iii) (iv)

A.(b) (c) (a) (d)
B.(b) (c) (d) (a)
C.(c) (b) (a) (d)
D.(c) (b) (d) (a)

Exam Year(s)

UGC NET - 2012,

Answer: B

OLAP, on-line analytical processing, is carried out on a data warehouse (b), and OLTP, on-line transaction processing, is carried out on a relational database management system (c). A decision tree is a classification technique (d), and a neural network is used here for regression (a), as the key pairs them. So the code is (b), (c), (d), (a), option (B). Option (A) pairs the decision tree with regression, and options (C) and (D) pair OLAP with the RDBMS, so they are wrong.

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Data Warehouse provides

A.Transaction Responsiveness
B.Storage, Functionality Responsiveness to queries
C.Demand and Supply Responsiveness
D.None of the above

Exam Year(s)

UGC NET - 2012,

Answer: B

A data warehouse is a store of integrated, subject-oriented, historical data collected from many sources for analysis, and it provides storage and the functionality to respond quickly to the queries that analysis needs. Transaction responsiveness is the job of the OLTP system, which handles day-to-day transactions, and demand and supply responsiveness is not a feature of a warehouse. The answer is 'Storage, Functionality Responsiveness to queries', option (B).

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Repository of information gathered from multiple sources, storing under unified scheme at a single site is called as

A.Data mining
B.Meta data
C.Data warehousing
D.Database

Exam Year(s)

UGC NET - 2013,

Answer: C

A repository of information gathered from multiple sources and stored under a unified schema at a single site is called a data warehouse, so the answer is (C) data warehousing. It is built by integrating, cleaning and loading data from several operational databases, and it supports analysis and decision making. Data mining is the discovery of patterns from such data and is not the store itself, meta data is data about data, and a database is a general collection of data kept for one application. So (A), (B) and (D) do not describe a unified multi-source store.

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Cross_tab displays permit users to view ______ of multidimensional data at a time.

A.One dimension
B.Two dimensions
C.Three dimensions
D.Multidimensions

Exam Year(s)

UGC NET - 2013,

Answer: B

Cross-tab displays permit users to view two dimensions of multidimensional data at a time. A cross-tabulation shows the data as a table with one dimension along the rows and one along the columns, and the cells hold the aggregate values.

One dimension would give a simple list, and a table cannot show three or more dimensions at once without choosing a slice or nesting the headings. Option B is correct.

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