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Training, validation and testing data

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The three data sets the AI Act defines for high-risk systems: training data fits the model, validation data tunes it and guards against overfitting, and testing data gives an independent check before release 1. Keeping them separate, and proving it, is what stops test-set contamination.

Developed in
ch. 14, Data for training and testing
Chapters
ch. 14, Development
Contrast with
Test-set contamination
Source
1 numbered reference, listed below

Where it is used

13 chapters of the Body of Knowledge use the term. Each link opens the first section that does.

Training, validation and testing data: mentions per chapter33 mentions of the term across 13 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapterOther chapter01 Definition: 1 mention01 Definition104 The Stack: 1 mention04 The Stack108 Regulatory Map: 3 mentions08 Regulatory Map310 Reading List: 3 mentions10 Reading List313 Risk Management: 2 mentions13 Risk Management214 Development: 2 mentions14 Development215 Deployment: 6 mentions15 Deployment616 Fairness & XAI: 3 mentions16 Fairness & XAI317 Incidents: 2 mentions17 Incidents218 EU AI Act: 2 mentions18 EU AI Act219 Privacy & AI: 3 mentions19 Privacy & AI321 AI Laws Worldwide: 4 mentions21 AI Laws Worldwide422 Principles & Standards: 1 mention22 Principles & Standards1No mentions in the other 10 chaptersSource: the Body of Knowledgev0.5.0
Training, validation and testing data: mentions per chapter33 mentions of the term across 13 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapterOther chapter0001 Definition: 1 mention101020304 The Stack: 1 mention10405060708 Regulatory Map: 3 mentions30810 Reading List: 3 mentions310111213 Risk Management: 2 mentions21314 Development: 2 mentions21415 Deployment: 6 mentions61516 Fairness & XAI: 3 mentions31617 Incidents: 2 mentions21718 EU AI Act: 2 mentions21819 Privacy & AI: 3 mentions3192021 AI Laws Worldwide: 4 mentions42122 Principles & Standards: 1 mention12223Source: the Body of Knowledge v0.5.0
Mentions per chapter How often each chapter names the term, with the chapters the glossary cross-references drawn solid. The longest bar is where to read the term in use; bars spread across many chapters mark a term that runs through the discipline.
Mentions as a table
Mentions of Training, validation and testing data per chapter
ChapterMentionsCross-referenced
00 Preface0No
01 Definition1No
02 Why Now0No
03 Values & Principles0No
04 The Stack1No
05 Patterns0No
06 The Role0No
07 Maturity Model0No
08 Regulatory Map3No
10 Reading List3No
11 AI Defined0No
12 Governance Program0No
13 Risk Management2No
14 Development2Yes
15 Deployment6No
16 Fairness & XAI3No
17 Incidents2No
18 EU AI Act2No
19 Privacy & AI3No
20 Existing Law0No
21 AI Laws Worldwide4No
22 Principles & Standards1No
23 AI Agents0No

Patterns that use this term

4 pattern pages use the term, most mentions first.

Training, validation and testing data: related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedContrastColour: stack layer of the pattern01 Govern-as-Code02 InventoryTraining, validation and testing dataRelated terms (3)AI Act (EU) · RelatedAI Act (EU)Notified body · RelatedNotified bodyRegurgitation · RelatedRegurgitationContrast with (1)Test-set contamination · ContrastTest-set contaminationPatterns using it (4)AI Threat Model, 5 mentions · Uses the termAI Threat ModelDataset Admission Gate, 3 mentions · Uses the termDataset Admission GateDownstream Use Register, 2 mentions · Uses the termDownstream Use RegisterVendor / Model Due-Diligence Gate, 1 mention · Uses the termVendor / Model Due-Diligence
Training, validation and testing data: related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedContrastColour: stack layer of the pattern01 Govern-as-Code02 InventoryRelated terms (3)AI Act (EU) · RelatedAI Act (EU)Notified body · RelatedNotified bodyRegurgitation · RelatedRegurgitationContrast with (1)Test-set contamination · ContrastTest-set contaminationPatterns using it (4)AI Threat Model, 5 mentions · Uses the termAI Threat ModelDataset Admission Gate, 3 mentions · Uses the termDataset Admission GateDownstream Use Register, 2 mentions · Uses the termDownstream Use RegisterVendor / Model Due-Diligence Gate, 1 mention · Uses the termVendor / Model Due-DiligenceTraining,validation andtesting data
The term's neighbourhood Terms related to this one on solid edges, terms it is often confused with on dashed edges, and the patterns that use it most in the colour of their layer. Follow a dashed edge to check the distinction before you use either term.
Neighbourhood as a table
Neighbourhood of Training, validation and testing data
FamilyItemRelation
Related termsAI Act (EU)Related
Related termsNotified bodyRelated
Related termsRegurgitationRelated
Contrast withTest-set contaminationContrast
Patterns using itAI Threat Model, 5 mentionsUses the term
Patterns using itDataset Admission Gate, 3 mentionsUses the term
Patterns using itDownstream Use Register, 2 mentionsUses the term
Patterns using itVendor / Model Due-Diligence Gate, 1 mentionUses the term
  • Notified body

    A conformity assessment body designated under the EU AI Act to carry out third-party conformity assessment of high-risk AI systems.

  • Regurgitation

    A model reproducing memorised training data verbatim, including personal data, whether prompted deliberately (training-data extraction) or not.

  • AI Act (EU)

    Regulation (EU) 2024/1689, the EU's horizontal, risk-tiered law for AI, amended by the Digital Omnibus.

Sources

  1. [1] Regulation (EU) 2024/1689 (AI Act), consolidated text as amended by Regulation (EU) 2026/1744 (Digital Omnibus on AI, in force 27 Jul 2026; definitions in Art. 3, incl. 3(1), 3(3) to 3(14), 3(14b), 3(20), 3(22), 3(23), 3(29) to 3(32), 3(49), 3(55) to 3(57), 3(60), 3(61), 3(63), 3(68); Arts. 4, 5, 6 (incl. 6(3) third subparagraph, profiling), 9, 10, 11, 13, 14, 15, 17, 22 to 27 (incl. 26(11)), 40, 41, 43, 47, 48, 50, 53 (incl. 53(1)(c)), 55, 57, 60, 72, 73, 86; Annexes I, III, IV). Publications Office of the EU (EUR-Lex). 2026-07-27. https://eur-lex.europa.eu/eli/reg/2024/1689/2026-07-27/eng (verified: primary)

Definitions of legal terms paraphrase the cited text, which governs. Dated statements are as of .

Cite this term

García Aibar, J. (2026). Training, validation and testing data. In AI Governance Engineering: The Thesis & Body of Knowledge (v0.5.0), Glossary. https://doi.org/10.5281/zenodo.22956197. https://aigovernanceengineer.com/glossary/training-validation-and-testing-data. CC BY 4.0

BibTeX

@misc{aige2026trainingvalidationandtestingdata,
  author  = {Jorge García Aibar},
  title   = {{Training, validation and testing data}},
  note    = {Glossary, AI Governance Engineering: The Thesis \& Body of Knowledge, version 0.5.0},
  year    = {2026},
  doi     = {10.5281/zenodo.22956197},
  url     = {https://aigovernanceengineer.com/glossary/training-validation-and-testing-data}
}