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Data Dictionary — "Format" Is Not "Type"

The Hamilton and Alexandra College · Year 12 · 2026

The single most common data-dictionary error is writing a data type in the Format column. They are not the same thing. This page explains the difference, shows you what correct entries look like, and maps to the VCAA band descriptors.

The core distinction

Type is the kind of data — what category it belongs to.

Format is the storage or display pattern — the exact shape the value takes.

These are different answers to different questions:

Question Column Example answer
What kind of data is this? Type Integer
What does a valid value look like? Format 999999 (fixed 6 digits)

If you write Integer in the Format column, you have answered the wrong question. A marker sees that and knows you have conflated two concepts.

Format notation key

The format strings use a small set of symbols — memorise these:

Symbol Meaning
9 or N One digit (0–9)
X One uppercase letter
x One lowercase letter
YYYY Four-digit year
MM Two-digit month
DD Two-digit day
Separator (, . -) Literal separator character

So 999999 means "exactly six digits". Xxxxxxxxxxxxxxx means "one uppercase letter followed by lowercase letters — the number of x characters shows the maximum length".

Worked example — a complete data dictionary

These rows come from a client-management system. Read across each row and notice that Type and Format sit in separate columns and say different things.

Field Type Size Format Example
id Integer 6 999999 201940
firstName Text 50 Xxxxxxxxxxxxxxx Jane
lastName Text 50 Xxxxxxxxxxxxxxx Smith
DOB Date/time 8 YYYY-MM-DD 2001-07-19
clubMember Boolean 1 true/false true
memberYears Integer 2 NN 6
sales FloatingPoint 8 NN,NNN.NN 12,543.76

Notice what each Format entry tells you that the Type alone does not:

  • id is an Integer — but the Format 999999 tells you it is always 6 digits, not 1 or 2.
  • firstName is Text — but Xxxxxxxxxxxxxxx tells you it starts with a capital and the rest are lowercase.
  • DOB is Date/time — but YYYY-MM-DD fixes it to ISO format, not DD/MM/YYYY or MM-DD-YYYY.
  • sales is FloatingPoint — but NN,NNN.NN specifies a thousands separator and exactly 2 decimal places.

Why Format matters

Format entries do three jobs in your design documentation:

  • Data consistency — every value entered follows the same shape, so comparisons and sorting work correctly.
  • Validation — your software can reject an entry that does not match the pattern (e.g., a date typed as 19-07-01 instead of 2001-07-19).
  • Readability — another developer reading your data dictionary can reproduce the exact storage structure without guessing.

A Format column filled with type names (Integer, String, Boolean) gives you none of these benefits — it duplicates the Type column and adds no information.

VCAA band levels — what's required at each step

VCAA defines a data dictionary as specifying variables, arrays, and GUI objects with reference to data types, data structures, and data sources. The level descriptors build upward:

Level What you must include
Level 3 Reference to data types (Integer, Text, Boolean, Date/time, FloatingPoint)
Level 5 Data types and data structures (arrays, records — not just scalar variables)
Level 7 Data types, data structures and data sources (where does each value come from — user input, database, calculation?)

You cannot skip levels. If your dictionary has no data structures, you cannot claim Level 5 or above.

Common mistakes

Mistake 1: Format = Type

Format: Integer

Write the pattern instead: 999999, NN, etc. If you cannot write a pattern, leave a note and revisit — but do not copy the Type column.

Mistake 2: Missing data sources at Level 7

(no Source column, or Source column left blank for half the rows)

Every field at Level 7 needs a source. "User input", "calculated from sales total", "retrieved from customer database" — these are all valid. Blank is not.

Mistake 3: Vague sizes

Size: large

Size must be a number — the number of characters, bytes, or digits the field can hold. If you do not know, look at your data (the longest plausible value) and choose a round number that covers it.

Mistake 4: Only scalar variables

A dictionary that lists only individual variables but no arrays or records cannot score Level 5 or above. If your design uses a list of items or a record structure, include it.

🎬 Watch

Note

Video coming soon.

🎯 Watch for: how an experienced developer reads a Format string and immediately knows the exact shape of valid data — something the Type alone can never tell you.

Check Your Understanding

  1. A student writes Text in the Format column for a lastName field. What is the mistake, and what should they write instead?
Answer

Text is a type, not a format. It duplicates the Type column and adds nothing. The correct Format entry is Xxxxxxxxxxxxxxx — one uppercase letter followed by lowercase letters, with the number of x characters indicating maximum length (e.g. 15 for a 15-character maximum).

  1. Your data dictionary has variables and arrays but no data sources. Which VCAA level can you reach, and which is out of reach?
Answer

You can reach Level 5 (data types and data structures). Level 7 is out of reach because it requires data sources as well. Add a Source column and fill it in for every row to unlock Level 7.

  1. What does the Format string NN,NNN.NN tell you that the Type FloatingPoint does not?
Answer

It tells you the value uses a thousands separator (,) and is stored to exactly two decimal places. FloatingPoint alone does not specify either of these — you could have 12543.7 or 12,543.759 and both would be valid floats, but only 12,543.76 matches the format.

See also

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