Figure 1.

Prototypical schemas for laboratory machines: (a) direct model for an instrument, (b) using inheritance to sub-class instrument types, (c) using meta-data. Diagrams show entity type relationships and primary and foreign keys (marked 'PK' and 'FK'. respectively). The "bird's foot" symbols are a standard notation indicating that single instances from one type associate with multiple instances in the other. The "arrow" notation indicates inheritance.