The post relates to a stackoverflow question on DB design and my answer there.
To summarize relationships:
- One report can list many observations, an observation can appear in many reports.
- One subject (under observation) can undergo many observations, an observation relates to one subject only.
- An observation is of a specific type, there can be many observations of the same type.
- Measurement and trait are types of observations. Measurement is a numeric observation, like height. Trait is a descriptive observation, like color.
This is a simplified model based on Fowler's observation pattern, for more details see Analysis Patterns by Martin Fowler.