Full Answer
Why do we load dimension table before fact table?
This is why all the dimension tables must be populated first before we populate the fact tables: because we need the surrogate keys on the dimension tables to translate the fact table natural keys. This is the very basic and the very heart of data warehouse loading, so it is important to understand it.
Is fact table a normalized or denormalized table?
Typically, data warehouse schemas follow a star or snowflake schema, where a centralized “fact” table containing events is surrounded by satellite tables called “dimensions” with the descriptive attributes related to the fact table. Fact tables are denormalized, and dimension tables are normalized.
What are the types of dimension tables?
Types of Dimension Tables in a Data Warehouse
- Types of Dimension Tables
- Slowly Changing Dimensions (SCD)
- Rapidly Changing Dimensions
- Junk Dimensions
- Inferred Dimensions
- Conformed Dimensions
- Degenerate Dimensions
- Role Playing Dimensions
- Shrunken Dimensions
- Static Dimensions
Are dimension tables and domain tables the same thing?
is that domain is a geographic area owned or controlled by a single person or organization while dimension is a single aspect of a given thing. to mark, cut or shape something to specified dimensions. Other Comparisons: What's the difference?
What is the difference between a fact table and a dimension table?
The data in both the tables can be in normal text format, while fact tables can have numbers along with the texts.
How many columns are there in a fact table?
Fact tables mostly have two columns, one for foreign keys that helps to join them with a dimension table and others that contains the value or data that need to be analyzed. It mostly contains numeric data. It grows vertically and it contains more records and fewer attributes. Start Your Free Data Science Course.
What is dimension table?
Dimension Table. A dimension table contains the dimensions along which the values of the attributes are taken in the fact table. Dimension tables are small in size, contains only several thousand rows but the size can be increased occasionally. These tables are associated with a fact table through foreign keys.
What are the dimensions that have reference to any other dimension table called?
Outrigger Dimensions: The dimensions that have reference to any other dimension table are called as outrigger dimensions. Shrunken Rollup Dimensions: The dimensions which are the subdivision of columns and rows of the base dimension are called Shrunken Rollup dimensions.
Why isn't the dimension table normalized?
Normalization: Dimension table is not normalized because normalization splits the data and creates additional tables which decrease the efficiency of the query execution as it must pass through these additional tables when it wants to recover measurements from the fact table for any corresponding attribute in the dimension table.
What is a concatenated key in a fact table?
Such key is called a concatenated key which uniquely identifies the row of the fact table.
What is the grain of a fact table?
Fact Table Grain: Grain of the table means the level of the detail or the deepness of the information that is stored in the fact table. The level must be the highest for designing an efficient fact table.
What is a fact table?
Fact table is a measurable event for which dimension table data is collected and is used for analysis and reporting.
What is dimension table?
Dimension table: A dimension table contains dimensions of a fact. They are joined to fact table via a foreign key. Dimension tables are de-normalized tables. The Dimension Attributes are the various columns in a dimension table. Dimensions offers descriptive characteristics of the facts with the help of their attributes.
What is companion table to fact table?
Companion table to the fact table contains descriptive attributes to be used as query constraining.
What is a secondary dimension called?
A dimension may have a reference to another dimension table. These secondary dimensions called outrigger dimensions. This kind of Dimensions should be used carefully.
Why is it important to have a single physical dimension?
A single physical dimension helps to reference multiple times in a fact table as each reference linking to a logically distinct role for the dimension.
What is a degenerate dimension?
Degenerate dimension is without corresponding dimension. It is used in the transaction and collecting snapshot fact tables. This kind of dimension does not have its dimension as it is derived from the fact table. They are used when the same fact table is paired with different versions of the same dimension.
Where is the dimension table located?
Fact table is located at the center of a star or snowflake schema, whereas the Dimension table is located at the edges of the star or snowflake schema.
What is dimension table?
Dimension tables contain details about each instance of an object. For example, the items dimension table would contain a record for each item sold in the store. It might include information such as the cost of the item, the supplier, color, sizes, and similar data.
What Is a Fact Table Grain?
When designing a fact table, developers must pay careful attention to the grain of the table, which is the level of detail contained within the table.
What is the difference between a dimension table and a fact table?
Dimension table contains the attributes on that truth table calculates the metric. 2. In fact table, There is less attributes than dimension table.
What is the attribute format of a fact table?
The attribute format of fact table is in numerical format and text format. While the attribute format of dimension table is in text format. 6. It comes after dimension table. While it comes before fact table. 7. The number of fact table is less than dimension table in a schema.
What is a reality table?
A reality or fact table’s record could be a combination of attributes from totally different dimension tables. The Fact Table or Reality Table helps the user to investigate the business dimensions that helps him in call taking to enhance his business.
When to choose dimensions for fact table?
Choose the dimensions – once the grain of the fact table is stated clearly, it is time to determine dimensions for the fact table.
How to create a fact table?
Here is an overview of four steps to designing a fact table described by Kimball: 1 Choosing business process to a model – The first step is to decide what business process to model by gathering and understanding business needs and available data 2 Declare the grain – by declaring a grain means describing exactly what a fact table record represents 3 Choose the dimensions – once the grain of the fact table is stated clearly, it is time to determine dimensions for the fact table. 4 Identify facts – identify carefully which facts will appear in the fact table.
What is transactional fact table?
Transactional – Transactional fact table is the most basic one that each grain associated with it indicated as “one row per line in a transaction”, e.g., every line item appears on an invoice. Transaction fact table stores data of the most detailed level, therefore, it has a high number of dimensions associated with it.
What are the different types of measures in a fact table?
Measure types. Fact table can store different types of measures such as additive, non-additive, semi-additive. Additive – As its name implied, additive measures are measures which can be added to all dimensions.
Where is the fact table in a data warehouse?
A fact table is used in the dimensional model in data warehouse design. A fact table is found at the center of a star schema or snowflake schema surr ounded by dimension tables.
Fact Table
Dimension Table
- A dimension table contains the dimensions along which the values of the attributes are taken in the fact table. Dimension tables are small in size, contains only several thousand rows but the size can be increased occasionally. These tables are associated with a fact table through foreign keys. These tables are de-normalized. The dimension table contains hierarchical relationships a…
Key Differences Between Fact Table and Dimension Table
- Let us discuss some of the major differences between Fact Table vs Dimension Table. 1. Fact Table contains the values or measurements of the attributes of the dimension table. 2. Fact table comprises of fewer attributes and more records whereas the dimension table comprises of lesser records and more attributes. 3. The fact table grows vertically while the dimension table grows h…
Conclusion
- In this article, we read about the fact table vs dimension table and the differences between them in detail. These tables are important for developing a schema. Dimension table is a companion of the fact table and both are necessary for each other.
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