Representation-based database notional machines map from a database context to a context that is not a familiar real-world analogy but rather an alternative representation. Such representations can take various forms, including diagrams, physical manipulatives, role-plays, and verbal explanations.
Some representations are handmade (e.g., a diagram drawn on a board) while others are machine-generated (e.g., a visualization produced by a tool).
We collected and organized the following 11 representation-based notional machines:
| Symbol | Concept |
|---|---|
| the table-looking rectangles | the input relations |
| the shaded area | the output |
| Symbol | Concept |
|---|---|
| set | tables |
| boxes | processing steps |
| Symbol | Concept |
|---|---|
| boxes | relations / tuples |
| vertical lines | attributes |
| Symbol | Concept |
|---|---|
| Rectangles | normal forms |
| Symbol | Concept |
|---|
| Symbol | Concept |
|---|
| Symbol | Concept |
|---|---|
| relationship | set |
| instance of a relationship | set element |
| Symbol | Concept |
|---|---|
| Symbol | Concept |
|---|---|
| arrows | join among rows |
| Symbol | Concept |
|---|---|
| circles | sets |
| shaded area | result of the operation |
| Symbol | Concept |
|---|---|
| rectangles | tables / relations |
| horizontal stripes | rows |
| circled portions within the stripes | specific attribute values in those rows |
| double-sided arrow | equi-join condition |
A notional machine is a pedagogic device to assist the understanding of some aspect of programs or programming. To something along the lines of A notional machine is a pedagogical tool designed to support the understanding of programs, programming, and other aspects of computing such as databases.
