Most Asked Oracle ETL Interview Questions and Answers
What is ODS (operation data source)?
ODS – Operational Data Store.
ODS Comes between staging area & Data Warehouse. The data is ODS will be at the low level of granularity.
Once data was poopulated in ODS aggregated data will be loaded into into EDW through ODS.
What is the difference between etl tool and olap tools?
ETL tool is ment for extraction data from the legecy systems and load into specified data base with some process of cleansing data.
ex: Informatica,data stage ….etc
OLAP is ment for Reporting purpose.in OLAP data avaliable in Mulitidimectional model. so that u can write smple query to extract data fro the data base.
ex: Businee objects,Cognos….etc
What is the metadata extension?
Informatica allows end users and partners to extend the metadata stored in the repository by associating information with individual objects in the repository. For example, when you create a mapping, you can store your contact information with the mapping. You associate information with repository metadata using metadata extensions.
Informatica Client applications can contain the following types of metadata extensions:
Vendor-defined. Third-party application vendors create vendor-defined metadata extensions. You can view and change the values of vendor-defined metadata extensions, but you cannot create, delete, or redefine them.
User-defined. You create user-defined metadata extensions using PowerCenter/PowerMart. You can create, edit, delete, and view user-defined metadata extensions. You can also change the values of user-defined extensions.
What are the various test procedures used to check whether the data is loaded in the backend, performance of the mapping, and quality of the data loaded in INFORMATICA?
The best procedure to take a help of debugger where we monitor each and every process of mappings and how data is loading based on conditions breaks.
I am new to SAS, can anybody explain the process of extracting data from source systems,storing in ODS and how data modelling is done?
There are various ways of Extracting Data from Source Systems.For example , You can use a DATA step, an Import Process .It depends with your input data styles. What kind of File/database it is residing in. Storing ur data in an ODS can be done thru an ODS stmt/export stmt/FILE stmt, again which depends on the file & data format ,You want your output to be in.
Techniques of Error Handling – Ignore, Rejecting bad records to a flat file, loading the records and reviewing them (default values)?
Rejection of records either at the database due to constraint key violation or the informatica server when writing data into target table.These rejected records we can find in the badfiles folder where a reject file will be created for a session.we can check why a record has been rejected.And this bad file contains first column a row indicator and second column a column indicator.
These row indicators or of four types
T- Truncated data,
And depending on these indicators we can changes to load data successfully to target.
What is Full load & Incremental or Refresh load?
Full Load: completely erasing the contents of one or more tables and reloading with fresh data.
Incremental Load: applying ongoing changes to one or more tables based on a predefined schedule.
How to determine what records to extract?
When addressing a table some dimension key must reflect the need for a record to get extracted. Mostly it will be from time dimension (e.g. date >= 1st of current mth) or a transaction flag (e.g. Order Invoiced Stat). Foolproof would be adding an archive flag to record which gets reset when record changes.
Do we need an ETL tool? When do we go for the tools in the market?
It is used to Extract(E) data from multiple source systems(like RDBMS,Flat files,Mainframes,SAP,XML etc) transform(T) them based on Business requirements and Load(L) in target locations.(like tables,files etc).
Need of ETL Tool: An ETL tool is typically required when data scattered accross different systems.(like RDBMS,Flat files,Mainframes,SAP,XML etc).
Can we use procedural logic inside Infromatica? If yes how, if now how can we use external procedural logic in informatica?
Yes, you can use advanced external transformation. for more detail you can refer the manual of informatica transformation guide in that advance external transformation. You can use c++ language on unix and c++, vb vc++ on windows server.
Can we override a native sql query within Informatica? Where do we do it? How do we do it?
Yes,we can override a native sql query in source qualifier and lookup transformation.
In lookup transformation we can find “Sql override” in lookup properties.by using this option we can do this.
What are parameter files? Where do we use them?
Parameter file defines the value for parameter and variable used in a workflow, worklet or session.
How can we use mapping variables in Informatica? Where do we use them?
Yes. we can use mapping variable in Informatica.
The Informatica server saves the value of mapping variable to the repository at the end of session run and uses that value next time we run the session.