Fact tables provide the (usually) additive values that act as independent variables by which dimensional attributes are analyzed. Fact tables are often defined by their grain.
Full Answer
What is an example of an additive fact table?
The most flexible and useful facts are fully additive; additive measures can be summed across any of the dimensions associated with the fact table. An example of a fully additive measure is sales (purchases from a store). You can add hourly sales to get the sales for a day, week, month, quarter, or year. You can add sales across stores or regions.
What is an example of a fully additive measure?
An example of a fully additive measure is sales (purchases from a store). You can add hourly sales to get the sales for a day, week, month, quarter, or year. You can add sales across stores or regions.
What is a semi-additive fact table?
Semi-additive - measures that can be added across some dimensions. A fact table might contain either detail level facts or facts that have been aggregated (fact tables that contain aggregated facts are often instead called summary tables). Special care must be taken when handling ratios and percentage.
How to design a fact table?
Here is overview of four steps to designing a fact table described by Kimball: Choose the dimensions – once grain of fact table is stated clearly, it is time to determine dimensions for the fact table. Identify facts – identify carefully which facts will appear in the fact table.
What is additive fact table?
Additive Facts are Facts that can be summed up through all of the dimensions in the Fact table. For example, if there is a retail store and if we want to identify the total sales which have happened in the last six months, we can group the records of the last six months and get the summed up (aggregated) value.
What is additive fact example?
Additive facts are those facts which give the correct result by an addition operation. Examples of such facts could be number of items sold, sales amount etc. Non-additive facts can also be added, but the addition gives incorrect results. Some examples of non-additive facts are average, discount, ratios etc.
What is additive and semi additive fact?
Additive: Additive facts are facts that can be summed up through all of the dimensions in the fact table. Semi-Additive: Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others.
What are the three types of fact tables?
There are three types of fact tables and entities: Transaction. A transaction fact table or transaction fact entity records one row per transaction. Periodic.
What is the best example of an additive measure?
An additive measure uses SUM to aggregate over any attribute. The sales amount is a perfect example of an additive measure. Indeed, the sales amount for all customers is the sum of the individual sales for each customer; at the same time, the amount over a year is the sum of the amounts for each month.
What are additive measures?
Additive measures are measures that can be aggregated across all of the dimensions in the fact table, and are the most common type of measure. Additive measures are used across several dimensions for summation purposes.
What is semi-additive fact with example?
Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others. For example if you have the number of items in the warehouse for each day, you can sum up the items for each day (total warehouse of the day), but it make no senso to sum up in the year.
What is non additive?
Definition of nonadditive 1 : not having a numerical value equal to the sum of values for the component parts. 2 : of, relating to, or being a genetic effect that is not additive nonadditive effects of epistasis.
What is semi-additive measures?
A semi-additive measure is one that is to be summed for some dimensions, but should not be summed across some other dimensions. For the dimensions over which the measure is not additive, a different aggregation rule must be specified.
Can we join 2 fact tables?
The answer for both is "Yes, you can", but then also "No, you shouldn't". Joining fact tables is a big no-no for four main reasons: 1. Fact tables tend to have several keys (FK), and each join scenario will require the use of different keys.
Which of the following is an example of non additive facts?
Profit margins are non-additive. If a department has two employees, and one employee has sold an item with a 55% profit margin and the other has sold an item with a 45% profit margin, the profit margin for the department is not 100%.
How many fact tables are there?
There are four types of fact tables: transaction, periodic snapshot, accumulating snapshot and factless fact tables.
What is a semi-additive fact?
Semi-Additive: Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others. Non-Additive: Non-additive facts are facts that cannot be summed up for any of the dimensions present in the fact table. Let us use examples to illustrate each of the three types of facts.
What are the different types of facts?
There are three types of facts: 1 Additive: Additive facts are facts that can be summed up through all of the dimensions in the fact table. 2 Semi-Additive: Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others. 3 Non-Additive: Non-additive facts are facts that cannot be summed up for any of the dimensions present in the fact table.
Why are inventory levels and financial account balances semi-additive?
Inventory levels and financial account balances are semi-additive because they are additive across all dimensions except time. Here the Current Balance measure is semi-additive because adding up all the current balances for a given account for each day of the month doesn’t give any useful information.
Can you store percentages in fact tables?
However, it is considered as a good practice that to never store percentages or ratios in fact tables but only calculate these in the BI tools. It only stores the numerator and denominator in the fact table, which then can be aggregated and then can then be used for calculating the ratio or percentage in BI tool.
What is a fact table?
A Fact table in a Data Warehouse system is nothing but the table that contains all the facts or the business information, which can be subjected to analysis and reporting activities when required. These tables hold fields that represent the direct facts, as well as the foreign fields that are used to connect the fact table with other dimension tables in the Data Warehouse system. A Data Warehouse system can have one or more fact tables, depending on the model type used to design the Data Warehouse.
What is semi additive measure?
Semi- additive are those measures that are added to some of the dimensions and not to all the dimensions and non-additive measures are stored fundamental units of measurement for a business process. Sparse Data: There are records that have attributes containing null values or measures. They provide no information.
What is snapshot in statistics?
The snapshot gives the state of things at a particular instance of time or “picture of the moment”. It normally includes more non-additive and semi-additive facts. It helps to review the cumulative performance of the business at regular and predictable intervals of time. In this, the performance of an activity at the end of each day or a week or a month or any other time interval is represented, unlike the transaction fact table where a new row is added for the occurrence of every event. But snapshot fact tables or periodic snapshots are dependent on the transaction fact table to get the detailed data present in the transaction fact table. The periodic snapshot tables are mostly dense and can be large as transaction fact tables. Let us see an example of the periodic snapshot of the sales of the same grocery shop as in the transaction fact table.
Is a periodic snapshot a transaction fact table?
The periodic snapshot tables are mostly dense and can be large as transaction fact tables. Let us see an example of the periodic snapshot of the sales of the same grocery shop as in the transaction fact table. 3. Accumulating Fact Tables.
What is a semi-additive table?
Semi-additive - measures that can be added across some dimensions. A fact table might contain either detail level facts or facts that have been aggregated (fact tables that contain aggregated facts are often instead called summary tables). Special care must be taken when handling ratios and percentage.
What is a fact table?
In data warehousing, a fact table consists of the measurements, metrics or facts of a business process. It is located at the center of a star schema or a snowflake schema surrounded by dimension tables. Where multiple fact tables are used, these are arranged as a fact constellation schema. A fact table typically has two types of columns: those that contain facts and those that are a foreign key to dimension tables. The primary key of a fact table is usually a composite key that is made up of all of its foreign keys. Fact tables contain the content of the data warehouse and store different types of measures like additive, non additive, and semi additive measures.
What is the primary key of a fact table?
The primary key of a fact table is usually a composite key that is made up of all of its foreign keys. Fact tables contain the content of the data warehouse and store different types of measures like additive, non additive, and semi additive measures. Fact tables provide the (usually) additive values that act as independent variables by which ...
What are the different types of fact tables?
Types of fact tables. There are four fundamental measurement events, which characterize all fact tables. Transactional. A transactional table is the most basic and fundamental. The grain associated with a transactional fact table is usually specified as "one row per line in a transaction", e.g., every line on a receipt.
What is an accumulating snapshot table?
An accumulating snapshot table often has multiple date columns, each representing a milestone in the process. Therefore, it's important to have an entry in the associated date dimension that represents an unknown date, as many of the milestone dates are unknown at the time of the creation of the row.
What is additive measure?
Additive measures. The numeric value in a fact table that is more flexible is an additive measure. For each dimension you can even sum up. If you want to know the total sales of your company you can easily sum up all the sales.
What is semi-additive facts?
Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others. For example if you have the number of items in the warehouse for each day, you can sum up the items for each day (total warehouse of the day), but it make no senso to sum up in the year.
What is a fact table?
In the most general sense, fact tables are the measurements of a business process. They hold mostly numeric data and correspond to an event rather than a particular report. The most important feature of a fact table, besides measures, is grain. Grain defines what level of detail is observed for a particular event.
What is the common factor in fact tables?
However, before we delve into what these different fact tables do, let’s talk about an important common factor: sparsity, or the proportional amount of data stored in a fact table. Sparsity is related to grain, and it has an effect on query performance.
What are some examples of measures in a fact table?
They occur when all the important information about the dimension is already in the fact table. Examples include various control header numbers, ticket numbers, order numbers, etc. Measures (i.e. metrics or business facts) in a fact table can be: Additive: summable across any dimension.
What is periodic snapshot?
Periodic snapshot tables record the cumulative performance of the business at predefined periods of time. A predetermined interval for taking snapshots is the key: daily, weekly, monthly, etc. The results are saved in the periodic snapshot fact table.
How many rows are there in a fact_retail_sale table?
Suppose we fill the fact_retail_sale table from two sources: a database table with 100,000 rows and a spreadsheet with 20,000 rows. These rows are filled on a yearly basis. The dimension tables are: dates (365 rows), products (100 rows) and stores (1,000 rows).
What is the grain of a transaction fact table?
The grain of this type is one row per transaction, or one row per line on a transaction. The grain of a transaction fact table is a point in space and time. They hold the smallest of business details.
What are technical columns? What are some examples?
Technical columns are useful for auditing and low-level maintenance of the model. Timestamps, which are used to mark when insertions or updates occur in the fact table, are a common example of a technical column.
Example of Fact Table
Measure Types
- Fact table can store different types of measures such as additive, non-additive, semi-additive. 1. Additive– As its name implied, additive measures are measures which can be added to all dimensions. 2. Non-additive– different from additive measures, non-additive measures are measures that cannot be added to all dimensions. 3. Semi-additive– semi-ad...
Types of Fact Tables
- All fact tables are categorized by three most basic measurement events: 1. 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 …
Designing Fact Table Steps
- Here is overview of four steps to designing a fact table described by Kimball: 1. Choosing business process to 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…
Characteristics of Fact Table
Types of Fact Table
How Does It Work in A Data Warehouse?
Advantages of Fact Table
- It contains quantitative information for analysis.
- It containing performance metrics are usually normalized.
- It can contain different measures like additive, semi-additive and non-additive.
Conclusion
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