SAP BW Interview Questions - 2
What is Star Schema?
In Star Schema model, Fact table is surrounded by dimensional tables. Fact table is usually very large, that means it contains millions to billions of records. On the other hand dimensional tables are very small. Hence they contain a few thousands to few million records. In practice, Fact table holds transactional data and dimensional table holds master data.
The dimensional tables are specific to a fact table. This means that dimensional tables are not shared to across other fact tables. When other fact table such as a product needs the same product dimension data another dimension table that is specific to a new fact table is needed.
This situation creates data management problems such as master data redundancy because the very same product is duplicated in several dimensional tables instead of sharing from one single master data table. This problem can be solved in extended star schema.
What is extended star schema?
In Extended Star Schema, under the BW star schema model, the dimension table does not contain master data. But it is stored externally in the master data tables (texts, attributes, hierarchies).
The characteristic in the dimensional table points to the relevant master data by the use of SID table. The SID table points to characteristics attribute texts and hierarchies.
This multistep navigational task adds extra overhead when executing a query. However the benefit of this model is that all fact tables (info cubes) share common master data tables between several info cubes.
Moreover the SID table concept allows users to implement multi languages and multi hierarchy OLAP environments. And also it supports slowly changing dimension.
What is slowly changing dimension?
Dimensions those changes with time are called slowly changing dimension.
What is fact table?
Fact table is the collection if facts and relations that means foreign keys with the dimension. Actually fact table holds transactional data.
What is dimension table?
Dimension table is a collection of logically related descriptive attributes that means characteristics.
What is modeling?
It is an art of designing the data base. The design of DB depends on the schema and the schema is defined as representation of tables and their relationships.
What is an info cube?
Info cube is structured as star schema (extended) where a fact table is surrounded by different dim table that are linked with DIM'ids. And the data wise, you will have aggregated data in the cubes.
How many tables does info cube contain?
Actually info cube contains two tables’ E table and F (fact) table.
What is the maximum no. of dimensions in info cube?
16(3 are sap defines and 13 are customer defined)
What are the minimum no of dimensions in info cube?
4(3 Sap defined and 1 customer defined).
What are the 3SAP defined dimensions?
The 3 SAP defined dimensions are…..
1. Data packet dimension (P)…..it contains 3characteristics.a) request Id (b) Record type (c) Change run id
2. Time dimension (T)….it contains time characteristics such as 0calmonth, 0calday etc
3. Unit Dimension (U)…it contains basically amount and quantity related units.
What is the maximum no. of key figures?
233
What is the maximum no. of characteristics?
248
What is the model of the info cube?
Info cube model is extended star schema.
What are the data types for the characteristic info object?
There are 4types:
1. CHAR
2. NUMC
3. DATS
4. TIMS
How you’ll write date in BW?
YYYYMMDD
In Star Schema model, Fact table is surrounded by dimensional tables. Fact table is usually very large, that means it contains millions to billions of records. On the other hand dimensional tables are very small. Hence they contain a few thousands to few million records. In practice, Fact table holds transactional data and dimensional table holds master data.
The dimensional tables are specific to a fact table. This means that dimensional tables are not shared to across other fact tables. When other fact table such as a product needs the same product dimension data another dimension table that is specific to a new fact table is needed.
This situation creates data management problems such as master data redundancy because the very same product is duplicated in several dimensional tables instead of sharing from one single master data table. This problem can be solved in extended star schema.
What is extended star schema?
In Extended Star Schema, under the BW star schema model, the dimension table does not contain master data. But it is stored externally in the master data tables (texts, attributes, hierarchies).
The characteristic in the dimensional table points to the relevant master data by the use of SID table. The SID table points to characteristics attribute texts and hierarchies.
This multistep navigational task adds extra overhead when executing a query. However the benefit of this model is that all fact tables (info cubes) share common master data tables between several info cubes.
Moreover the SID table concept allows users to implement multi languages and multi hierarchy OLAP environments. And also it supports slowly changing dimension.
What is slowly changing dimension?
Dimensions those changes with time are called slowly changing dimension.
What is fact table?
Fact table is the collection if facts and relations that means foreign keys with the dimension. Actually fact table holds transactional data.
What is dimension table?
Dimension table is a collection of logically related descriptive attributes that means characteristics.
What is modeling?
It is an art of designing the data base. The design of DB depends on the schema and the schema is defined as representation of tables and their relationships.
What is an info cube?
Info cube is structured as star schema (extended) where a fact table is surrounded by different dim table that are linked with DIM'ids. And the data wise, you will have aggregated data in the cubes.
How many tables does info cube contain?
Actually info cube contains two tables’ E table and F (fact) table.
What is the maximum no. of dimensions in info cube?
16(3 are sap defines and 13 are customer defined)
What are the minimum no of dimensions in info cube?
4(3 Sap defined and 1 customer defined).
What are the 3SAP defined dimensions?
The 3 SAP defined dimensions are…..
1. Data packet dimension (P)…..it contains 3characteristics.a) request Id (b) Record type (c) Change run id
2. Time dimension (T)….it contains time characteristics such as 0calmonth, 0calday etc
3. Unit Dimension (U)…it contains basically amount and quantity related units.
What is the maximum no. of key figures?
233
What is the maximum no. of characteristics?
248
What is the model of the info cube?
Info cube model is extended star schema.
What are the data types for the characteristic info object?
There are 4types:
1. CHAR
2. NUMC
3. DATS
4. TIMS
How you’ll write date in BW?
YYYYMMDD
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