Data Warehousing Concepts

Fact tables: Have any measurable value in it and it contain foreign key of all the dimension table.

Dimension Tables: Do not have any numeric value, and it shows the characteristics that describe a transaction.

Dimension:It gives description about fact.

Fact:Is knows as Key Identifier(Measures)

EX:
Empno Empname Sal Deptno
1 A 20,000 201
2 B 15,000 203

All facts are numeric

The shortcut keys are related to a specific window and will only work in that window. It is part of the name of a menu item or button, where it can be underlined, and is available (without modifiers) ...

hotkey: which is used to open r close an application.....
shortcutkey: used to perform actions with in the application....

May be Applet.getImage(new URL(...)) can be used to convert java applet into image file.

Java applets are not used in DWH. So its irrelevant question in DWH concepts group.

Surrogate keys are advisable for a few different reasons: 1. In a large enterprise environment with many data sources to pull from you will inevitably come across a data feed that either does not con...

Full Load is the entire data dump load taking place the very first time. Gradually to synchronize the target data with source data, there are further 2 techniques:- Refresh load - Where the existing...

In simple words, after transforming the data it is loaded into the DWH. Two distinct groups of tasks form the data loading function. When you complete the design and construction of the DWH and go liv...

Let me just give the Data quality problems. If I explain it will go page by page. 1. Dummy values in source system fields. 2. Absence of data in source system fields. 3. Multipurpose fields. 4. Crypt...

You have to test all the transformations in your ETL and write negative scenarios.

By definition, surrogate key is a system generated key. This key is used as Primary key in the Dimensions. Why? There are generally two principles to be applied when choosing Primary keys for the Dim...

In slowly changing dimensions to have unique key in a record.

ODS is a datastore that contains wide breath of data but not very deep(aggregated not atomic levels), OLTP is used to describe the transaction profile that will access the ODS, small predictable trans...

1. ODS  - It is a decision support system which contains snapshot of current data for day to day analysis. This may include little history data also   OLTP - It is a trasaction system t...

In fact table because of we are using summerized data, we will be including all dimensional's table's primrary key as a Foreign key for their relationship.The key should me in the Lowest Level...

Two main reasons to generate and maintain a surrogate key on DW side:1. If your DW has multiple sources for a dimension or fact, the PK ID fields can have same values from different sources. The only ...

Time is a semi additive measure.  If you have a fact table containing information on the number of items in stock in a warehouse, then it would never make sense to aggregate these measures over t...

We cannot do any measures on it.
Values are generally text in nature.
We maintain a status to track the event.

Ex-Visitors to the office.
List of people for the web click.

A fact which has possibly NO measure but can be seen as count of occurences or events is called factless fact. example: no. of accidents per month on roads.If i elaborate more, no. of accidents i...

SCD-1 (Current)Overwriting the old values in the dimension record. SCD-2 (History and Current)Creating an additional dimension record at the time of the change with the new attribute values. ...

SCD means Slowly Changing Dimension. The price of the product, address of the person, name of the city are few examples of SCD.There are three methods to capture SCD.Type 1: Overwriting the old values...

Non additive facts are facts that cannot be summed up for any of the dimensions present in the fact table.

A fact that cannot be logically added between records, such as average, and that must be combined in a computation with other facts before being added across records.

A data mart is a group of subjects that are organized in a way that allows them to assist departments in making specific decisions. For example, the advertising department will have its owndata mart, ...

Data Mart is subset of dataware house deal with single area of data and is organized by quick analysis.

Innmons approach is better to load data from Data Marts.

1. The direction of the data load depends on the approach that was adopted while designing the Warehouse and the datamart. If the top down approach, which Kimbal mentions is used, then data will ...

 Hierarchy contains many levels, every level contain an attribute.

Idan Halfon

hi nice ans u given and i think we can add number of of levels under hirarchy

Triggers are stored procedures that are invoked when certain conditions or events occur. The granularity and flexibility of the conditions and events that cause a trigger to fire are database spec...

An MDDB is generally used where large number of aggregations and summarizations are required along with a very fast retrieval of data.Here the data is stored in the form of multidiemnsional cube(howev...

A MDDB is generally used where large number of aggregations and summarizations are required along with a very fast retrieval of data.Here the data is stored in the form of multidiemnsional cube(howeve...