Hierarchical Task Analysis (HTA)

Goal-based task decomposition method from the human-factors / ergonomics tradition. Originated with Annett et al. (1971); mainstream procedure codified by Stanton (2006). Still the dominant task-analysis method in human factors >40 years after its introduction (sources/2010-salmon-hta-vs-cwa).

Core idea

An operator (human or machine) is "required to do X" to achieve a super-ordinate goal. Decompose that goal into sub-goals, operations, and plans (sequence/conditions for operations). Recurse until the redescription is "good enough" — a judgement call, not a fixed depth.

Output: a goal hierarchy tree with plans at each level.

Procedure (Stanton 2006)

State the overall goal.
State subordinate operations.
State the plan (sequence/conditions).
Check adequacy of redescription (revise if needed).
Consider first/next suboperation → recurse if further redescription required, else terminate.
Repeat until all operations terminated.

Data collection

No single method. The standard combo is:

Observation (shadowing)
SME interviews / questionnaires
Walkthroughs (think-aloud while operator performs the task)
User trials
Documentation review

Iteration with SMEs is mandatory — a single pass never produces a satisfactory hierarchy.

Task-decomposition template (Kirwan & Ainsworth 1992)

For each leaf-level step, capture:

Initiating event / cue
Information requirements
Interface features (controls / displays)
Actions required
Decisions required
Complexity / difficulty
Outputs
Feedback

→ This template is directly reusable as an observation-protocol field-note structure for BPM process discovery.

Granularity

HTA can decompose to button-press level — e.g. "click on drop-down menu, click right mouse button to activate mapping menu, click on map to drop waypoint." This is appropriate for error prediction (SHERPA), training design, and interface evaluation — it is far too fine for BPM process discovery, which should remain at activity level or higher (sources/2018-dumas-fundamentals-of-bpm-ch5-discovery §6.1 warns against step-level descent).

Relation to BPM discovery

HTA is not a BPM method, but its discipline maps cleanly:

HTA step	BPM discovery analogue
State overall goal	Process boundaries (sources/2018-dumas-fundamentals-of-bpm-ch5-discovery §5.3 step 1)
State subordinate operations	Identify main activities (§5.3 step 2) / Sharp's TRAC subprocesses (sources/2014-sharp-using-scope-models)
State plan	Control flow (§5.3 step 4)
Check adequacy + recurse	Interview → Modeling → Validation cycle (§5.2.2)
SME iteration mandatory	Dumas's ≥2 interview iterations per expert
Multi-method default	Dumas's §5.2.4 "mix methods" recommendation

Use for BPM observation sessions: adopt HTA's 8-field decomposition template as the observation field-note structure. Recursion stops at the activity level (not the button-press level).

sources/2010-salmon-hta-vs-cwa — primary source.
methods/process-discovery-methods — observation method.
concepts/process-discovery
syntheses/qualitative-discovery-method-selection-matrix — observation row.
syntheses/interview-structuring-for-process-models — iteration cycle.
Cognitive Work Analysis (CWA) — formative/constraint-based counterpart (Vicente 1999) (referenced-not-ingested).
Kirwan & Ainsworth (1992) A Guide to Task Analysis (referenced-not-ingested).
Annett et al. (1971) Task Analysis (referenced-not-ingested — HTA origin paper).