Data Modeling – Fact Table Effective Practices

Database Table
Database Table

Here are a few guidelines for modeling and designing fact tables.

Fact Table Effective Practices

  • The table naming convention should identify it as a fact table. For example:
    • Suffix Pattern:
      • <<TableName>>_Fact
      • <<TableName>>_F
    • Prefix Pattern:
      • FACT_<TableName>>
      • F_<TableName>>
    • Must contain a temporal dimension surrogate key (e.g. date dimension)
    • Measures should be nullable – this has an impact on aggregate functions (SUM, COUNT, MIN, MAX, and AVG, etc.)
    • Dimension Surrogate keys (srky) should have a foreign key (FK) constraint
    • Do not place the dimension processing in the fact jobs

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Data Modeling – Database Table Field Ordering Effective Practices

Field order can help the performance on inserts and updates and, also, keeps developer and users from having to search entire table structure to be sure they have all the keys, etc.

Table Field Ordering

  1. Distribution Field Or Fields, if no distribution field is set the first field will be used by default.
  2. Primary Key Columns (including Parent and Child key fields)
  3. Foreign Key Columns (Not Null)
  4. Not Null Columns
  5. Nullable Columns
  6. Created Date Timestamp
  7. Modified (or Last Updated) Date Timestamp
  8. Large text Fields
  9. Large binary Columns or Binary Field references

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Where do data models fit in the Software Development Life Cycle (SDLC) Process?

In the classic Software Development Life Cycle (SDLC) process, Data Models are typically initiated, by model type, at key process steps and are maintained as data model detail is added and refinement occurs.

The Concept Data Model (CDM) is, usually, created in the Planning phase.   However,  creation the Concept Data Model can slide forwarded or backward, somewhat, within the System Concept Development, Planning, and Requirements Analysis phases, depending upon whether the application being modeled is a custom development effort or a modification of a Commercial-Off-The-Shelf (COTS) application.  The CDM is maintained, as necessary, through the remainder of the SDLC process.

The Logical Data Model (LDM) is created in the Requirement Analysis phase and is a refinement of the information entities of the Concept Data Model. The LDM is maintained, as necessary, through the remainder of the SDLC process.

The Physical Data Model (PDM) is created in the Design phase to facilitate the creation of accurate detail technical designs and actual database creation. The PDM is maintained, as necessary, through the remainder of the SDLC process.

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