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DWH: Week 5, Inventory Use Case Notes, Size Estimation of a Data Warehouse…
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Inventory Use Case Notes
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Therefore, For semi-additive facts, we get the average, not the sum.
When a measure is static, also called semi across the date dimension and possible other dimensions.
Then the measure if aggregated across time by average over number of time periods.
Static Measures (Inventory, Financial, Intensity)
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Star Schema
What
- The fact table contain the primary information in the data warehouse.
- The dimension tables contain information about the entries for a particular attribute in the fact table.
- The dimension tables don't interact with each other, There is no relationship between them.
- Relations in Star Schema are 1 to N.
- It is consists of a fact table and the dimensions of the star.
- A simple data warehouse schema.
Why
- Highly used in commercial products
- Many analytical or BI tools support star schema
- Easy to interpret and explain for end-user.
- Schema is extendible for other facts (records in fact table) and dimensions
- Simplicity is the key of Star Schema
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Snowflake Schema
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What
- Normalized means a dimension is divided into another sub dimension(s)
- Consists of a central fact table and normalized dimensions
Schema
Three Definitions
A definition of a database, defines the structure and the type of content that data items can contain within the structure.
In a relational database, the schema defines tables and attributes of each table and relationships among them.
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Revisited Concepts
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Granularity
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If data is truly huge, move inactive data to overflow storage