ETL Testing Interview Questions and Answers
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Best ETL Testing Interview Questions and Answers
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ETL testing is one of the software testings. Software testing is defined as the testing which is conducted to make sure that the actual results match the expected results without any defects. So ETL testing has a similar purpose with its software. ETL stands for Extract-Transform-Load and is defined as the process of uploading the data from the source system to the data warehouse. A data warehouse is a place where one can find the company’s consolidated data.
Q1) What is ETL?
Answer: ETL stands for Extract-TrAnswerform-Load. It is an important component in the data warehouse with which one can manage the data of any business.
- The extract does the reading of the data from the database.
- Transform does the conversion of data such that it can be used for analysis and reporting.
- Load does the allocation of data to the respective database.
Q2) What are the operations included in ETL testing?
Answer: Following are the operations included in ETL testing:
- Verification of the conversion of data to a required business format.
- Verification of the loading of data to the respective data warehouse without any cut short of the main data.
- Ensuring that there are no invalid data and if found any, replacing them with the default data.
- Ensuring the time frame to improve the performance and expandability of the loading.
Q3) What are the different types of data warehouse applications?
Answer: Following are the different types of data warehouse applications:
- Processing of information.
- Processing of analytics.
- Data mining.
Q4) What is the difference between data mining and data warehousing?
Answer: Following is the table explaining the difference between data mining and data warehousing:
|Parameter||Data mining||Data warehousing|
|Definition||Data mining refers to extracting information from hidden patterns.||Data warehousing refers to the collection of data from various places and storing them in one place.|
|Key features||Outcomes that are likely can be predicted.
The patterns can be discovered automatically
|Data can be obtained within the fixed time frame.
Heterogeneous data can be used to make the final database.
|Advantages||The marketing of the product is direct.
Detailed analysis of trends in the marketplace.
|Productivity and performance are better.
Q5) Name the types of tools used in ETL.
Answer: Following are the different types of tools that are used in ETL:
- Warehouse builder from Oracle.
- Decision stream from Cognos.
- Business warehouse from SAS.
- Enterprise ETL server from SAS.
- Business object XI.
Q6) Define fact.
Answer: Fact is defined as the central component related to the multi-dimensional model. The multi-dimensional model contains measures that are to be analyzed.
Q7) What are the different types of facts?
Answer: Following are the different types of facts:
- Additive facts
- Semi-additive facts
- Non-additive facts
Q8) What do Cubes mean?
Answer: Cubes are defined as the data processing units that consist of facts tables and dimensions obtained from the data warehouse. It is used for multi-dimensional analysis.
Q9) What does OLAP Cubes mean?
Answer: OLAP cubes stand for Online Analytics Processing cubes. It is used for storing multi-dimensional data on a large scale. It consists of dimensions that are segregated on the basis of measures.
Q10) What does the tracing level mean?
Answer: The tracing level is defined as the amount of data that is stored in the log files.
Q11) What are the different types of tracing levels?
Answer: Following are the two different types of tracing levels:
Q12) Explain the types of tracing levels.
Answer: Normal level is the first type of tracing levels that are used to explain the tracing level in a detailed manner. The verbose level is the second type of levels that are used to explain the tracing level at every row.
Q13) What do you mean by the term “Grain of Fact”?
Answer: Grain of fact is also known as Fact Granularity and is defined as the storage place of the fact information.
Q14) Define measures.
Answer: Measures are defined as the numeric data on the basis of the columns in a fact table.
Q15) What is a factless fact schema?
Answer: A factless fact schema is the fact table without any measures. It is used to view the number of occurrences of the events.
Q16) What is the transformation?
Answer: TrAnswerformation is defined as the storage place where the generation, modification, and passing of data take place.
Q17) How many types of transformation are there?
Answer: There are two types of transformation:
- Active transformation
- Passive transformation
Q18) What is an active transformation?
Answer: Active transformation is used to modify the rows of data and also the number of input rows that are passed through them. An example of an active transformation is Filter transformation.
Q19) What is a passive transformation?
Answer: Passive transformation is used to get the input and output data in the same number of rows. An example of passive transformation is Lookup transformation.
Q20) What is the use of Lookup transformation?
Answer: Following are the uses of Lookup transformation:
- With the use of column value, the related value can be found from the table.
- The dimension of the table changes slowly.
- Lookup example formation is used for the verification of the existing records.
Q21) What is partitioning?
Answer: Partitioning is defined as the division of the data storage to improve performance. There are two types of partitioning:
- Round-robin partitioning
- Hash partitioning
Q22) What is round-robin partitioning?
Answer: Round-robin partitioning is a type of partitioning which is done to distribute the data uniformly in all the division and is applied when the number of rows for processing are equal.
Q23) What is hash partitioning?
Answer: Hash partitioning is a type of partitioning which is done for grouping of the data based on the keys and is used for ensuring that the processed groups are in the same partition. Hush partitioning finds application in the Informatica server.
Q24) What is the advantage of using the DataReader Destination Adapter?
Answer: The advantage of using DataReader Destination Adapter is that the records and columns in the memory are postulated such that the data from the DataFlow task is available for full consumption.
Q25) What is Informatica?
Answer: Informatica is a software development company that offers products related to data integration. Products from Informatics are used by ETL, data quality, master data management, data masking, etc.
Q26) Name the list of transformations that are available on Informatica.
Answer: Following are the list of transformations that are available on Informatica:
- transformation for rank.
- transformation for sequence generator.
- transformation for controlling transactions.
- transformation for source qualifier
- transformation for normalizing.
Q27) What is filter transformation?
Answer: Filter transformation is an active transformation which is used for filtering the records on the basis of filter condition.
Q28) What is SSIS?
Answer: SSIS stands for SQL Server Integration Service. It is one of the components of the Microsoft SQL Server database which is used for conducting a wide range of data integration. SSIS is used in ETL testing because it is fast and flexible and also the movement of the data from one database to another becomes easy with the help of SSIS.
Q29) How to update the table with the help of SSIS?
Answer: Following are the ways to update the table with the help of SSIS:
- By using SQL command.
- By using a staging table.
- With the help of cache.
- By using the script task.
Q30) Name the two types of ETL testing that are available.
Answer: Following are the two types of ETL testing that are available:
- Application testing
- Data eccentric testing
Q31) Define dimensions.
Answer: Dimensions are the place where the summarized data are stored.
Q32) Why do we need ETL testing?
Answer: Following are the reasons why we need ETL testing:
- With the help of ETL testing, one can check for the efficiency and speed of the process.
- To keep an eye on the trAnswerfer of the data from one system to the other.
- To get familiar with the ETL process before running the entire business using ETL.
Q33) What do you mean by the term “staging area”?
Answer: During the process of data integration, the data is stored at a placed temporarily so that the data is cleaned and checked for any duplication. This storage area is known as a staging area.
Q34) Define ETL mapping sheets.
Answer: ETL mapping sheet is a place where one can find all the information related to the source file which included all the rows and columns. This sheet is very helpful for ETL tool testing.
Q35) Name a few ETL bugs.
Answer: Following is the list of ETL bugs:
- Bug related to ECP.
- Bug related to load conditioning.
- Source related bugs.
- Bugs related to calculations.
- Bug related to the user interface.
Q36) Name a few test cases.
Answer: Following is the list of test cases:
- Issues related to correctness.
- Data checker
- Validation on mapping doc
Q37) What is the use of mapping doc validation?
Answer: With the help of mapping doc validation, one can check if the provided information is available in the mapping doc.
Q38) What is the purpose of data check as a test case?
Answer: With the help of the data check test case, one can easily get the information related to data check, number check, and null check.
Q39) What is the use of the correctness issue test case?
Answer: As the name suggests, the correctness issues test case helps in understanding the misspelled data, null data, and inaccurate data.
Q40) What is the difference between power mart and power center?
Following is the table explaining the difference between power mart and power center:
|Power mart||Power center|
|It is used only for the local storage||It is used for local and global storage.|
|There is a specification for the conversion of local data into global||It can be used for the conversion of local data into global data|
|EPR sources are not supported||ERP sources such as SAP is supported|
|The main purpose of power mart is to process low volume data||The main purpose of power center is to process huge amount of data|
Q41) What is the difference between unconnected and connected lookup?
Answer: Following are the difference between unconnected and connected lookup:
|Unconnected lookup||Connected lookup|
|The cache used is static||The cache used can be either static or dynamic|
|Only a single output port can be used||Multiple output ports can be used|
|Only a single transformation can be used||Multiple transformations can be used|
Q42) What is the difference between OLAP tools and ETL tools?
Answer: Following is the table explaining the difference between OLAP tools and ETL tools:
|OLAP tools||ETL tools|
|OLAP tools are used for reporting data from the OLAP database||ETL tools are used for the extraction of data from the system and to load them at the specific database|
|Cognos is an example of the OLAP tool||Informatica is an example of the ETL tool|
Q43) What do understand by the term data purging?
Answer: Data purging is defined as the process of deleting junk data from the data warehouse.
Q44) What is bus schema?
Answer: Bus schema is used for identifying similar dimensions in various business processes. Bus schema provides standard information with precise dimensions.
Q45) What is schema objects?
Answer: Schema objects are the logical structures that are used for referring to the database. These objects are tables, indexes, database links, function packages, etc.
Q46) What is the purpose of a staging area?
Answer: Following are the purposes of staging area:
- Restructuring of the database for proper data extraction and transformation.
- CleAnswering data and transformation of values.
- Used for the replacement of key assignments.
Q47) Explain the following terms:
- Mapplet: This is used for arranging a set of transformations.
- Worklet: This is used for representing a specific set of tasks.
- Workflow: This is used as a set of instructions for the server to execute the tasks.
- Session: This is used as a set of definitions that are used for the commanding of a server while moving data from the target source.
Q48) Explain the steps for the extraction of SAP data using Informatica.
Answer: Following are the steps for the extraction of SAP data using Informatica:
- SAP data is extracted using Informatica by using the option called power connect.
- By installing and configuring the Power control tool.
Q49) What is the data source view?
Answer: Data source view is used for defining the relational schema that is used for the analysis of the service database.
Q50) What is the use of dynamic cache and static cache in connected and unconnected transformation?
Answer: Static cache is used for flat files while the dynamic cache is used for updating the master table by slowly changing the dimensions.