Interview Questions

1) How many types of approaches in DHW?

Two approaches: Top-down(Inmol approach), Bottom-up(Ralph Kimball)

2) Explain Star Schema?

Star Schema consists of one or more fact table and one or more dimension tables that are related to foreign keys. Dimension tables are De-normalized, Fact table-normalizedAdvantages: Less database space & Simplify queries.

3) Explain Snowflake schema?

Snow flake schema is a normalize dimensions to eliminate the redundancy.The dimension data has been grouped into one large table. Both dimension and fact tables normalized.

4) What is confirm dimension?

If both data marts use same type of dimension that is called confirm dimension.If you have same type of dimension can be used in multiple fact that is called confirm dimension.

5) Explain the DWH architecture?

It expalins about the System Arrangement of the Datawarehouse.

6) What is a slowly growing dimension?

Slowly growing dimensions are dimensional data,there dimensions increasing dimension data with out update existing dimensions.That means appending new data to existing dimensions.

7) What is a slowly changing dimension?

Slowly changing dimension are dimension data,these dimensions increasing dimensions data with update existing dimensions.

Type1: Rows containing changes to existing dimensional are update in the target by overwriting the existing dimension.In the Type1 Dimension mapping, all rows contain current dimension data.Use the type1 dimension mapping to update a slowly changing dimension table when you do not need to keep any previous versions of dimensions in the table.

Type2: The Type2 Dimension data mapping inserts both new and changed dimensions into the target.Changes are tracked in the target table by versioning the primary key and creating a version number for each dimension in the table.

Use the Type2 Dimension/version data mapping to update a slowly changing dimension when you want to keep a full history of dimension data in the table.version numbers and versioned primary keys track the order of changes to each dimension.

Type3: The type 3 dimension mapping filters source rows based on user-defined comparisions and inserts only those found to be new dimensions to the target.Rows containing changes to existing dimensions are updated in the target. When updating an existing dimension the informatica server saves existing data in different columns of the same row and replaces the existing data with the updates.

8) When you use for dynamic cache?

Your target table is also look up table then you go for dynamic cache .In dynamic cache multiple matches return an error.use only = operator.

9) what is lookup override?

Override the default SQL statement.You can join multiple sources use lookup override.By default informatica server add the order by clause.

10) we can pass the null value in lookup transformation?

Lookup transformation returns the null value or equal to null value.




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