Essential Terms

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# Essential Terms — C02

The Hamilton and Alexandra College · Year 12 · 2026

A glossary of every term you need to recognise and use correctly across C02. Click a term to expand its definition. Use this as a vocabulary self-check before your C2-1 (Poster Peer-Assessment) and C2-2 (Hand-Drawn Diagrams) validations — if you can't define a term in your own words, you can't defend it under questioning.

```mermaid
flowchart TD
    R["C02 vocabulary<br/>26 terms"]
    R --> G0["Data collection<br/>9 terms"]
    R --> G1["Context diagrams and DFDs<br/>7 terms"]
    R --> G2["Use case diagrams (UML)<br/>10 terms"]
```

*Where the C02 vocabulary sits, and how much of it is in each group — the 3 sections below follow the same order. Revise the heavy groups first.*

---

## Data collection

>| ### Close-ended questions
>| Questions that can be answered with a finite set of responses

>| ### Data
>| Raw, unprocessed facts and figures

>| ### Interview
>| A face-to-face meeting between people for consultative purposes

>| ### Observation
>| A method of data collection that involves physically observing how a system operates and how it is used

>| ### Open-ended questions
>| Questions where the number of potential answers is infinite

>| ### Qualitative data
>| Data that consists of descriptive details, usually gathered via surveys or interviews

>| ### Quantitative data
>| Data that can be easily processed in a statistical manner, usually composed of definite numbers

>| ### Report
>| A written document providing a summary or finding in relation to the context or system being analysed

>| ### Survey
>| A set of questions that ask for a response to be selected from a list of alternatives

---

## Context diagrams and DFDs

>| ### Context diagram
>| A visualisation of a system in its entirety that indicates the data that is passed into and out of the system

>| ### Data flow
>| The movement of a piece or collection of data within an information system, as shown in context diagrams and data flow diagrams (DFDs)

>| ### Data flow diagram (DFD)
>| A graphical visualisation of the flow of information within a system, including data provided by external entities

>| ### Data store
>| A representation of a collection of data that is stored in some way within a system

>| ### Entity
>| The users or external systems that interact with the system being created

>| ### Process (context diagram)
>| An abstract representation of the whole system being created

>| ### Process (data flow diagram)
>| An abstract representation of a function within a system

---

## Use case diagrams (UML)

>| ### Actor
>| An entity that can interact with the software solution as shown in a use case diagram

>| ### Association
>| A relationship between two elements in a use case diagram

>| ### Extend
>| A relationship between use cases where one use case has optional or additional functionality, which is represented in a use case diagram as a second use case

>| ### Generalisation
>| A parent-child relationship between two elements in a use case diagram

>| ### Include
>| A relationship between use cases where one use case is tied to, or relies upon, the functionality contained within another use case

>| ### Relationship
>| The connections between elements within a use case diagram

>| ### System boundary
>| A rectangle around relevant use cases that indicates the use cases that are within the scope of the solution

>| ### Unified Modeling Language (UML)
>| A general-purpose visual modelling language

>| ### Use case
>| A representation of the transactions or functions a user (actor) can complete in a system, as shown in a use case diagram

>| ### Use case diagram (UCD)
>| A method of describing how a user interacts with a system, using Unified Modeling Language (UML)

---

## See also

- [C02 home page](/sd/C02/C02-home) — everything else for this criterion
- [Context Diagram](/sd/C02/Context%20Diagram) — the highest-level view of your system
- [Context Diagram vs Data Flow Diagram](/sd/C02/Context%20Diagram%20vs%20Data%20Flow%20Diagram) — what changes between Level 0 and Level 1
- [What Is an Entity](/sd/C02/What%20Is%20an%20Entity) — entities aren't only people
- [Excalidraw Diagram Starters](/sd/C02/Excalidraw%20Diagram%20Starters) — pre-framed canvases for rehearsing all three diagrams