On context diagrams and data flow diagrams, students frequently draw only the humans they can think of — *"Student"*, *"Teacher"* — and miss every external system their software talks to. Missing an entity is a rubric error at every level above 3–4, because the rubric rewards *"relationships between the existing system, entities and data flows"*.

::: success

If all three answers are *"yes"* — it is an entity. Add it to your diagram.

If it is *inside* your system (a function you are writing, a class in your code, a database table your code owns) — it is **not** an entity. It belongs on the DFD as a process or data store.

::: danger

These are the entities students most often miss. Check whether *any* apply to your project before submitting.

| Any project with login | Authentication provider (e.g. Google OAuth) | Students think login is *"inside"* their app |

:::

::: info

The C2-2 rubric at **5–6** requires *"illustrates the relationships between the existing system, entities and data flows"*. *"Some errors or omissions exist"* is still acceptable at 5–6. But at **9–10**, *"no errors, inconsistencies or omissions exist"* — a missing entity **is** an omission, and omissions cost you the top band.

The most common C2-2 omission flagged in past years: the **email server or notification service** that every project needs but few students draw.