Friday, December 7, 2007

Data Warehouse Interview-6

What are the vaious ETL tools in the Market? Various ETL tools used in market are:
Informatica
Data Stage
Oracle Warehouse Bulider
Ab Initio
Data Junction

What is a CUBE in datawarehousing concept? Cubes are logical representation of multidimensional data.The edge of the cube contains dimension members and the body of the cube contains data values. What is data validation strategies for data mart validation after loading process ? Data validation is to make sure that the loaded data is accurate and meets the business requriments.
Strategies are different methods followed to meet the validation requriments

what is the datatype of the surrgate key ? Datatype of the surrgate key is either inteeger or numaric or number

What is degenerate dimension table? Degenerate Dimensions : If a table contains the values, which r neither dimesion nor measures is called degenerate dimensions.Ex : invoice id,empno

What is Dimensional Modelling? Dimensional Modelling is a design concept used by many data warehouse desginers to build thier datawarehouse. In this design model all the data is stored in two types of tables - Facts table and Dimension table. Fact table contains the facts/measurements of the business and the dimension table contains the context of measuremnets ie, the dimensions on which the facts are calculated.

What are the methodologies of data Warehousing.? Every company has methodology of their own. But to name a few SDLC Methodology, AIM methodology are stardadly used. Other methodologies are AMM, World class methodology and many more.

What is a linked cube? Linked cube in which a sub-set of the data can be analysed into great detail. The linking ensures that the data in the cubes remain consistent.

What is the main difference between Inmon and Kimball philosophies of data warehousing? Both differed in the concept of building teh datawarehosue..
According to Kimball …
Kimball views data warehousing as a constituency of Data marts. Data marts are focused on delivering business objectives for departments in the organization. And the data warehouse is a conformed dimension of the data marts. Hence a unified view of the enterprise can be obtain from the dimension modeling on a local departmental level.
Inmon beliefs in creating a data warehouse on a subject-by-subject area basis. Hence the development of the data warehouse can start with data from the online store. Other subject areas can be added to the data warehouse as their needs arise. Point-of-sale (POS) data can be added later if management decides it is necessary.
i.e.,
Kimball–First DataMarts–Combined way —Datawarehouse

Inmon—First Datawarehouse–Later—-Datamarts

What is Data warehosuing Hierarchy? Hierarchies
Hierarchies are logical structures that use ordered levels as a means of organizing data. A hierarchy can be used to define data aggregation. For example, in a time dimension, a hierarchy might aggregate data from the month level to the quarter level to the year level. A hierarchy can also be used to define a navigational drill path and to establish a family structure.

Within a hierarchy, each level is logically connected to the levels above and below it. Data values at lower levels aggregate into the data values at higher levels. A dimension can be composed of more than one hierarchy. For example, in the product dimension, there might be two hierarchies–one for product categories and one for product suppliers.

Dimension hierarchies also group levels from general to granular. Query tools use hierarchies to enable you to drill down into your data to view different levels of granularity. This is one of the key benefits of a data warehouse.

When designing hierarchies, you must consider the relationships in business structures. For example, a divisional multilevel sales organization.

Hierarchies impose a family structure on dimension values. For a particular level value, a value at the next higher level is its parent, and values at the next lower level are its children. These familial relationships enable analysts to access data quickly.

Levels
A level represents a position in a hierarchy. For example, a time dimension might have a hierarchy that represents data at the month, quarter, and year levels. Levels range from general to specific, with the root level as the highest or most general level. The levels in a dimension are organized into one or more hierarchies.

Level Relationships
Level relationships specify top-to-bottom ordering of levels from most general (the root) to most specific information. They define the parent-child relationship between the levels in a hierarchy.

Hierarchies are also essential components in enabling more complex rewrites. For example, the database can aggregate an existing sales revenue on a quarterly base to a yearly aggregation when the dimensional dependencies between quarter and year are known.

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