IBM i General Design Standards › Design Standards for Database Files › The Database of iSeries › Data Modeling › Useful Questions to Ask

Useful Questions to Ask

The following are usually critical questions to decide when data modeling is important:

• Is this item a file or a field? (for example, a thing or a property of a thing?)
• How is this item identified on the computer? What is the prime key of the database file that represents the item? In particular:
  • Is it unique?
  • Is it independent? (for example, the only key), or only unique within something else, (for example, subject to a superordinate key)?
  • Can it be changed? (in which case, it is probably not a key, or should not be used as a key).

Every file should be regarded as having at least one set of unique keys. For reference or master files (for instance a ‘Customer’ file, a ‘Product’ file), the unique key will usually be obvious. For transaction detail files (for example, Invoice details) it may not be strictly necessary to have a unique transaction key. It may be sufficient to have the records kept in arrival sequence, within major keys (for example, Invoice number). However, if you do this, it is more difficult to access a detail line by itself.