Data Warehousing Basics
What is surrogate key ? Where we use it explain with examples?
What are the steps to build the data warehouse?
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Answered by: ankeshjain
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Member Since Aug-2008 | Answered On : Aug 17th, 2008
1. Requirement gathering for BI reports
2. Identify the source databases
3. Designing source to target mappings
4. Designing DWH
5. Designing ETL jobs
6. Development of ETL jobs
7. Data load into DWH
The steps used to develop a DWH are 1. Gathers Operational Source System 2. Data Staging Area 3. Data presentation Area 4. Data Access Tool Lets have a detailed information about each stage: Operat...
We can create the dwh in two ways i.e
1. top down approach
2.bottom up approach
Answer posted by riaz ahmad on 2005-06-09 14:45:26: a dimensional table is a collection of hierarchies and categories along which the user can drill down and drill up. It contains only the textual attributes.
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Answered by: Edmond
Answered On : Apr 12th, 2007Let's be very clear. this is a very simple, and becomes a very confusing subject.
A fact table is an entity representing the numerical measurements of the business. A dimension table is the entity describing the textual representation of the business.
In a banking model, the account and balances are the measurements within the fact table, where customer name, social security, address, time period of the account, are the dimensions (customer/time).
Hope this answers the clarification.
In very simple termsFact : this contains all numeric attributesDimesion : this contains all non numeric , textual attributesIn order to rememberFact : Any answer to What user want to see is factfor ex...
Dimension table contains reference data which gives meaning to fact data. You can also view them as parameters across which you want to analyze the fact data.
What is the use of bridge table. Can give a simple example?
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Answered by: Sirini
Member Since Jun-2009 | Answered On : Jun 14th, 2009
An example of a Bridge table would be relationship table between student_master and courses_master. A Student may participate in multiple courses and obviously in a course there will be multiple students. In this scenario to maintain relationships between student_master and courses_master we need another table, which may be called, Student_courses. This table will have all relationships between Students and Courses.A bridge table is a table that only contains the keys between the two tables in a many-to-many relationship. These tables typically consist of mostly key fields, the primary keys of the two tables needing the many to many relationships. Sometimes there are more data elements, but often there are only two columns, both foreign keys.
Hi all... This is my view on bridge tables:Bridge table in simple can be called as reference tables. As the name indicates, this table can be used to link two tables with 1 reference id...
A table which maintained to define the relationship between two different tables is known as bridge tables. For example, say there are two tables one table with employee information (an employee table...
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Answered by: jaggu_mandya
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Member Since Jan-2008 | Answered On : Jan 17th, 2008
OLTP(1)---->ODS(2)------>DWH(3)-------->OLAP(4)------------>Reports(5)------>decision(6)
1-2 (extraction)
2-3 (Transformation and here ODS is itself staging area )
3-4-5 (Use of reporting tool and generate reports)
6-decision is taken i,e purpose of datawarehouse is served
I think this is right picture
Source System data ----------Extraction---------Transformation(Clenance the data according to business logics)(As dimensions)----------Takes data from the dimension tables in to fact tables using Surrogate keys---------------Load (As cubes)(In to the staging)
In some of the cases Pre Stage is also a intermediate phase between the OLTP environment and actual staging area.The prestage is one where dta clensing, data profiling nad data validation takes place....
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Answered by: saravanan
Answered On : Dec 2nd, 2005Surrogate key is a unique identification key, it is like an artificial or alternative key to production key, bz the production key may be alphanumeric or composite key but the surrogate key is always single numeric key. Assume the production key is an alphanumeric field if you create an index for this fields it will occupy more space, so it is not advisable to join/index, bz generally all the datawarehousing fact table are having historical data. These factable are linked with so many dimension table. if it's a numerical fields the performance is high
Surrogate key is a numeric or integer value in a table to identify each row uniquely. Primary key and surrogate key are same but surrogate key is a system generated value has a define incremental valu...
Surrogate key and primary key both are same, but point of application is different. Primary key is part of transactional system but surrogate key is part of analytical system. Surrogate key is used...