Oracle

What is surrogate key?

Oracle

Written by DBADMIN Wednesday, 19 May 2010 03:21

Surrogate key is a substitution for the natural primary key. It is just a unique identifier or number for each row that can be used for the primary key to the table. The only requirement for a surrogate primary key is that it is unique for each row in the table. It is useful because the natural primary key can change and this makes updates more difficult.Surrogated keys are always integer or numeric.

What is ER Diagram?

Oracle

Written by DBADMIN Wednesday, 19 May 2010 03:21

Entity Relationship Diagrams are a major data modelling tool and will help organize the data in your project into entities and define the relationships between the entities. This process has proved to enable the analyst to produce a good database structure so that the data can be stored and retrieved in a most efficient manner. An entity-relationship (ER) diagram is a specialized graphic that illustrates the interrelationships between entities in a database. A type of diagram used in data modeling for relational data bases. These diagrams show the structure of each table and the links between tables.

What are the Different methods of loading Dimension tables?

Oracle

Written by DBADMIN Wednesday, 19 May 2010 03:21

There are two different ways to load data in dimension tables. Conventional (Slow) : All the constraints and keys are validated against the data before, it is loaded, this way data integrity is maintained. Direct (Fast) : All the constraints and keys are disabled before the data is loaded. Once data is loaded, it is validated against all the constraints and keys. If data is found invalid or dirty it is not included in index and all future processes are skipped on this data.

What are slowly changing dimensions (SCD)?

Oracle

Written by DBADMIN Wednesday, 19 May 2010 03:21

SCD is abbreviation of Slowly changing dimensions. SCD applies to cases where the attribute for a record varies over time. There are three different types of SCD. 1) SCD1 : The new record replaces the original record. Only one record exist in database - current data. 2) SCD2 : A new record is added into the customer dimension table. Two records exist in database - current data and previous history data. 3) SCD3 : The original data is modified to include new data. One record exist in database - new information are attached with old information in same row.