Data Dictionary

Updated 06 Sep 2026

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What it is
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  a repository of all data items used in a system, including their definitions, formats, and relationships
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Purpose
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  helps determine the impact of a change to a data object
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  answers: "Where is this data object used?", "What else will have to change if we modify it?"
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  especially important for large projects with many data items
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Composite vs. elementary entries
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  composite — defined in terms of other data elements (e.g. fullName = title + firstName + middleName + lastName)
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  elementary — defined directly, often as a range or enumeration (e.g. title = [Mr | Mrs | Ms | Dr | Prof])
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Notation symbols
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  = — is composed of / is defined as
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  + — and
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  () — optional
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  {} — repetition (iteration)
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  [] — select one of several alternatives
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  ** — comment
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  @ — identifies the key attribute
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  | — separates alternatives inside []
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Iteration notation
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  min{X}max — X repeats at minimum min times and at maximum max times (e.g. 2{xy}5 allows "xyxy" through 5 repetitions)
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Organization rules
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  every DFD data flow must have a dictionary entry, and every composite entry must resolve down to elementary entries
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  no entry should exist that isn't used somewhere in the DFD, and no entry should be defined more than once
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  composite entries are listed first (alphabetically), then elementary entries (alphabetically)
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Notes
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  can be treated as a database for querying data object usage and relationships
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Related

Linked references 3

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Data Dictionary

What it is

Purpose

Composite vs. elementary entries

Notation symbols

Iteration notation

Organization rules

Notes

Related

Linked references 3