Top 60 Data Warehouse Interview Questions and Answers in 2021

In computing, a Data Warehouse, also called an enterprise data warehouse, is a system that is used for reporting and data analysis. It is a core component of business intelligence. Data warehouses are central repositories of the integrated data from one or multiple disparate sources.

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What is Data Warehousing used for?

Data warehouses are mainly used for analytical purposes and business reporting. Data warehouses usually store the historical data by integrating copies of the transaction data from different sources. Data warehouses also make use of real-time data feeds for reports that use the current, integrated information.

If you are planning to attend a Data Warehouse Interview, then it’s good to go through some of the Data Warehouse Interview Questions and Answers before you attend the interview. 

Top Data Warehouse Interview Questions and Answers

1. Define BI in simple terms? 

Business intelligence mainly consists of the technologies and strategies that are used by enterprises for the data analysis of business information. BI technologies aim to provide current, historical, and predictive views of business operations.

2. Define Data Analysis in terms of a Data Warehouse?

Data analysis is defined as the process of obtaining the raw data and converting them into useful information for decision-making. Here, the data is collected and analyzed to answer questions, disprove theories, or test hypotheses. The data initially obtained has to be processed or organized for analysis purposes.

3. Define Data Warehouse?

Data warehouses are mainly used for analytical purposes and business reporting. Data warehouses usually store the historical data by integrating copies of the transaction data from different sources.

4. Define Dimension Table? 

Data Warehouse Interview Questions - Dimension Table

A Dimension table is defined as a table in the star schema of the Data Warehouse. Data warehouses are usually built by using dimensional data models, which contain fact and dimension tables. We use the Dimension tables to describe dimensions; It consists of dimension keys, attributes, and values.

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5. Why is Data Warehouse subject-oriented?

A data warehouse is defined as subject-oriented because it mainly provides information around the subject rather than an organization’s ongoing operations. These subjects can be the product, suppliers,  customers, sales, revenue, etc.

Data Warehouse Interview Questions and Answers

6. Define OLAP and mention its types?

(OLAP)Online analytical processing is defined as an approach to answer (MDA)multi-dimensional analytical queries swiftly in computing. OLAP is part of the business intelligence, which also encloses relational databases, data mining, and report writing.

Types of OLAP:

  1. Hybrid OLAP
  2. Relational OLAP
  3. Multi-Dimensional OLAP
  4. Specialized SQL Servers

7. Can you list some of the Data Warehouse applications? 

Data Warehouse applications
  1. Banking Industry. 
  2. Finance Industry. 
  3. Consumer Goods Industry. 
  4. Government and Education. 
  5. Healthcare.
  6. Hospitality Industry

8. Define the Fact table?

A fact table in Data Warehouse contains the metrics, measurements, or facts of a business process. It is usually located at the center of the snowflake schema or a star schema surrounded by the dimension tables. The Fact tables’ primary key is a composite key made up of all of the foreign keys.

9. Differentiate between OLAP and OLTP?

OLAPOLTP
It has long transactions.OLTP  usually has short transactions.
It is mainly used to extract data for analysis that in turn helps in decision making.It focuses on insert, Updates, Delete information from the database.
It has complex queries.It has simple queries.
The tables in the OLAP database are usually not normalized.The tables in the OLTP database are usually normalized (3NF)

10. Differentiate between Data Warehouse and operational databases?

Data warehouseOperational databases
They are usually concerned with historical data.They are usually concerned with current data.
They are Non-volatile. We can add new data regularly. Once it is added, they are rarely changed.Data inside the operational systems are updated regularly according to the requirement.
It is mainly designed for the analysis of business measures by categories, subject area, and attributes.It is mainly designed for real-time business dealing and processes.

Data Warehouse Interview Questions and Answers

11. List the four stages of Data warehousing?

The four stages of Datawarehousing are listed below:

  1. Offline Operational Database
  2. Offline Data Warehouse
  3. Real-Time Datawarehouse
  4. Integrated Datawarehouse

12. List the functions performed by OLAP?

The OLAP functions are mainly grouped into these categories:

  1. Aggregate Functions
  2. Analytic Functions
  3. Hierarchical Functions
  4. Lag Functions
  5. OLAP DML Functions
  6. Rank Functions
  7. Share Functions
  8. Window Functions

13. Name the Schemas that a data warehouse system can implements?

A data Warehouse can implement 

  1. Star schema
  2. Snowflake schema
  3. Fact constellation schema

14. Define Data Mining? 

Data Mining

Data mining can be defined as a technique of analyzing unknown patterns of data. A data warehouse is a database system that is designed for analytical instead of transactional work. Data mining is usually a  method of comparing huge amounts of data to find the right patterns.

15. Define ER diagram in Data warehouse?

Entity Relationship Modeling is defined as a database modeling process that aims at establishing a visual representation of a system’s data. There are mainly  three basic elements in an ER Diagram, namely,

  1. Entity
  2. Attribute
  3. Relationship

Data Warehouse Interview Questions and Answers

16. Define Data Extraction?

Data extraction is defined as the technique of obtaining data from a SaaS platform or database so that it is replicated to a destination like a data warehouse that is designed to support (OLAP) online analytical processing. Data extraction is usually the first step in the data ingestion process known as ETL (extract, transform, and load).

17. Define ODS?

An Operational Data Store (ODS) is defined as a central database that mainly provides a snapshot of the new data from various transactional systems for operational reporting. It will allow the organizations to integrate data in its original format from different sources into a single destination and make it available for business reporting.

18. Define SCD?

Slowly Changing Dimensions (SCD) is the most commonly used advanced dimensional technique that is used in dimensional data warehouses. We use the Slowly changing dimensions when you wish to capture the changing data within the dimension time. 

19. Define Metadata?

Metadata in Data Warehouse is simply defined as data about data. The data that represents other data is called metadata. 

20. Differentiate between View and Materialized view?

ViewMaterialized View
Views are used when data has to be accessed infrequently, and the data in the table get updated on a frequent basis.The Materialized Views are generally used when the data has to be accessed frequently, and the data in a table do not get an update on a frequent basis.
A view is a virtual table that takes the output of the query and is used in place of tables.A materialized view is indirect access to table data by storing the results of the query in the separate schema.

Data Warehouse Interview Questions and Answers

21. List the types of SCD?

We have three types of SCD, they are:

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SCD 1: Here, a new record replaces the original record.

SCD 2: Here, the new record gets added to an existing client table.

SCD 3: Here, the original data gets changes to enter the new data.

22. What does Metadata Respiratory consist of?

The Metadata respiratory mainly consists of the definition of a data warehouse, operational metadata, business metadata, data for mapping from the operational environment to the data warehouse, and the algorithms required for summarization.

23. What is ETL?

ETL Process

In terms of computing, Extract, Transform, Load is a procedure of copying the data from one or multiple sources to a destination system that represents the data differently from a source or in a different factor than that of the source.

24. Define Snowflake Schema? 

In terms of computing, a snowflake schema is defined as a logical arrangement of tables in the multidimensional database in such a way that the entity-relationship diagram will resemble a snowflake shape. The snowflake schema is usually represented by a centralized fact table that is connected to various dimensions.

25. Define a Data Cube?

A data cube will allow the data to be modeled and viewed in various dimensions. A multidimensional data model is organized around the central theme, such as sales and transactions. A fact table usually represents this theme. Facts are nothing but numerical measures.

Data Warehouse Interview Questions and Answers

26. Define VLDB?

A Very Large Database (VLBD) is defined as a database that consists of a huge volume of data, such that it requires specialized architectural, processing, management, and maintenance methodologies.

27. Define Star Schema and Bus Schema?

In terms of computing, the Star Schema is defined as the simplest style of data mart schema, and it is the most widely used approach to develop data warehouses and dimensional data marts. The star schema usually contains one or multiple fact tables that references any number of dimension tables.

 A BUS Schema is mainly used to identify common dimensions across business processes, such as identifying conforming dimensions. BUS schema usually has conformed dimension and the standardized definition of facts. Here, all the Data Marts use the conformed dimensions and the facts without having them locally.

28. Define dimension in the Data Warehouse?

 The dimensions are defined as the entities w.r.t which an enterprise keeps the records.

29. Define Real-Time Data Warehousing?

Real-Time Data Warehousing usually captures the business data whenever it occurs. When the business activity is completed, the data will be available in the flow and is available to use instantly.

Data Warehouse Interview Questions and Answers

30. What is the core dimension?

The core dimension in Data Warehouse is nothing but a Dimension table that is used as a dedicated single fact table or data mart.

31. Define Data Mart?

A data mart is defined as a subject-oriented database that is often the partitioned segment of the enterprise data warehouse. The subset of data that is held in a data mart usually aligns with a particular business unit such as sales, finance, or marketing.

32. Define Aggregate tables?

Aggregate tables are defined as the tables that aggregate or roll up the data to one level higher than that of a base or a derived table. The functions like average, count, min, max is used with aggregate tables.

33. Explain the concept of loops in the data warehouse?

The Loops In Data Warehousing exists between the tables. If there is a loop present between the tables, then the query generation will take some more time and creates ambiguity. It is always advised to avoid a loop between the tables.

34. Define Virtual Warehouse?

We can say that a virtual warehouse is another term for the Data Warehouse. It usually collects and displays business data that are related to a specific moment in time, creating a snapshot of the condition of a business at that moment. Virtual warehouses will often collect data from different sources.

Data Warehousing Interview Questions and Answers

35. Define Factless fact tables?

Factless facts are defined as those fact tables that have no measures associated with the transaction. They are a simple collection of dimensional keys that defines the transactions or describe a condition for a time period of the fact.

36. Define XMLA?

XML for Analysis (XMLA) is defined as a SOAP-based XML protocol that is designed specifically for the universal data access to any standard multidimensional data source that is accessed over the HTTP connection. Analysis Services will use the XMLA as its only protocol while communicating with the client applications.

37. Name the phases involved in the Data warehouse delivery process?

The stages are that are involved in the Data warehouse delivery are listed below:

  1. IT strategy
  2. Education
  3. Business Case Analysis
  4. Technical Blueprint
  5. Build the version
  6.  History Load
  7. Ad hoc query
  8. Requirement Evolution
  9. Automation
  10. Extending Scope.
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38. How to load the time dimension?

The Time dimensions usually load through all the possible dates in a year, and it is done via a program. Here, 100 years will be represented with one row per day.

39. Differences between the Database and Data Warehouse?

DatabaseData Warehouse
It is two-dimensional data.It is multi-dimensional data.
High performance and availability.High flexibility.
The data size here is small.The data size here is large.
It is Relational data or Object-oriented data.It mainly deals with a large volume of data.

40. Explain the concept of Load Manager?

Load Manager is a component of a Data Warehouse that is responsible for the collection of data from the operating system and converts them into a usable form for the users. This component is responsible for the import and export of data from operational systems. 

Data Warehousing Interview Questions and Answers

41. Define Non-additive facts?

 Non-additive facts are defined as the facts that cannot be summed up for any of the dimensions that are present in the fact table.

42. Can you explain the types of Data Warehouses?

Enterprise Data Warehouse: In this type of Data Warehouse, the organizational data from different functional areas combine into a centralized way. It helps in the extraction and transformation of the data, which in turn provides a detailed overview of the object in the data model.

Operational Data Store: This type of data warehouse will help to access the data directly from the database and also supports the transaction processing. It aims to integrate contrast data from various sources that support different business operations later.

Data Mart: This type of data warehouse will store the data for a particular functional area. It also contains data in the form of subsets that stores in the data warehouse. It reduces the huge volume of data for the users to analyze and gain insights.

43. What is the function of a Load manager?

The main function of a Load manager is to  

  1. Extract data from the source system. 
  2. Then load the extracted data into a temporary data store. 
  3. To perform simple transformations into a structure that is similar to the one in the data warehouse.

44. What is conformed fact?

A conformed fact in Data Warehouse is defined as a shared fact designed to be used in a similar way across various data marts. In simple terms, the shared conformed facts mean that the same thing to various star schemas.

45. Explain who a warehouse manager is in simple terms?

Warehouse Managers work for warehouses where their main task is to supervise the receipt,  storage of goods, and dispatching of goods. Warehouse Managers also manage the warehouse staff, vehicles, and other equipment, oversee security, sanitation, and administrative functions.

Data Warehousing Interview Questions and Answers

46. Differentiate between Divisive Hierarchical Clustering and Agglomerative Clustering?

Divisive Hierarchical ClusteringAgglomerative Clustering
Here, it uses the top to bottom approach where the data at the parent level is read first, then at the child level.Here, the clusters will read from the bottom to the top.
Here, the division of clusters takes place. The parent cluster will be divided into smaller clusters. This division of clusters will continue until each of the clusters contains a single object.Here, the objects are present, and each object will build its cluster, and all these clusters will form a large cluster.

47. Define Active Datawarehousing?

Active Data Warehousing can be defined as the technical ability to capture the transactions when they change, and combine them into the warehouse, and also maintaining the batch or scheduled cycle refreshes. The active data warehouse will export decisions automatically to the On-Line Transaction Processing (OLAP) systems.

48. Define the Chameleon method in a Data warehouse?

In terms of Data Warehouse Chameleon, the representation will allow a huge dataset to create and operate successfully. The method will find the clusters that are used in the dataset by using the two-phase algorithm.

49. Define Summary Information?

Summary Information can be defined as a part of a Data Warehouse that aims to store predefined aggregations. These aggregations will be generated by the warehouse manager. Summary Information should be treated as transient. It will change the on the go to respond to the changing query profile.

Data Warehousing Interview Questions and Answers

50. Name the key columns in Fact and dimension tables?

Foreign keys of dimension tables are the primary keys of entity tables. Foreign keys of fact tables are the primary keys of dimension tables.

51. List the different tools used in ETL?

  1. Oracle
  2. Informatica
  3. Data Stage
  4. Data Junction
  5. Ab Initio
  6. Warehouse builder

52. What is the responsibility of a Query Manager?

The query manager is mainly responsible for 

  1. Directing the queries to suitable tables.
  2.  By doing the above, it will speed up the query request and response process. 
  3. The query manager is also responsible for scheduling the execution of the queries that are posted by the user.

53. Define Data cleaning?

Data cleaning is defined as the technique of removing the data that does not belong in the dataset.

54. Which among these are faster, Multidimensional OLAP or Relational OLAP?

Multidimensional OLAP is faster than Relational OLAP.

55. Can the Dimension table have a numeric value?

Yes, the Dimension table can have numeric value as they are the descriptive elements of the business.

Data Warehousing Interview Questions and Answers

56. List the approaches used to design the data warehouse?

The approaches used to design Data Warehouse are listed below:

  1. Inmon approach
  2. Kimball approach

57. How many dimensions can we select in the Slice operation?

Only one dimension can be selected for the slice operation.

58. What are the functions performed by OLAP?

The OLAP performs functions like

  1. Roll-up
  2. Drill-down
  3. Slice
  4. Dice
  5. Pivot.

59. List the types of Dimensional Modeling?

The types of Dimensional Modeling are listed below:

  1. Conceptual Modeling
  2. Logical Modeling
  3. Physical Modeling

60. List the benefits of a real-time Data Warehouse?

The benefits of a real-time Data Warehouse are listed below:

  1. It removes the batch window.
  2. It resolves the problems related to the ideal data load.
  3. It helps in easy decision-making.
  4. It will offer an optimized way to run the transformations in the database.
  5. It offers a quick recovery of data.

Good luck with your Data Warehouse Interview, and we hope our Data Warehouse Interview Questions and Answers were of some help to you. You can also check out our Agile Scrum Master Interview Questions and Answers.

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