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UX Glossary | H

Hierarchical task analysis diagram

Also: HTA diagram, Hierarchical task analysis

A tree that breaks a user goal into tasks and subtasks, with plans that say in what order or conditions they happen.

0 Prepare patient for scan 1 Check identity 2 Position patient 3 Select protocol 4 Confirm settings 2.1 Align table 2.2 Set coil 2.3 Check position Plan 0: 1, then 2 and 3 in any order, then 4 Plan 2: 2.1, then 2.2, then repeat 2.3 until still 0 Prepare patient for scan Plan 0: 1, then 2 and 3 in any order, then 4 1 Check identity 2 Position patient 3 Select protocol 4 Confirm settings 2.1 Align table 2.2 Set coil 2.3 Check position Plan 2: 2.1, then 2.2, then repeat 2.3 until still
Hierarchical task analysis, preparing a scan The boxes only list the work. The plans in green say how the parts combine: in order, in any order, or repeated until something is true.

A hierarchical task analysis (HTA) diagram takes a goal and splits it, level by level, into the tasks needed to achieve it. “Prepare a patient for a scan” breaks into checking identity, positioning, selecting a protocol and so on, and each of those breaks down again until you reach actions that need no further explaining. The method comes out of ergonomics research in the 1960s.

The part people skip: plans

The boxes are only half of it. Each parent box has a plan, a short statement of how its children combine: do 1, then 2 and 3 in any order, repeat 4 until the reading is stable, do 5 only if the alarm sounds. Without plans you have a work breakdown structure. With them you have a description of behaviour, including the loops and exceptions that a plain list hides.

HTA versus a flowchart

A flowchart shows sequence and decisions in one line of travel. An HTA shows containment: what belongs to what. It is easier to see the whole job on one page and to spot where a task contains an unreasonable number of subtasks, which usually means too much cognitive load.

In practice

Build it from observation, such as contextual inquiry, not from a procedure manual. It earns its keep in safety-critical and professional contexts: industrial controls, medical devices, cockpits. There, finding that an operator must remember three things while performing a fourth is a design finding, not an academic one.

Knowing the words is the easy part.

If you'd rather have someone apply them to your product, that's what I do.

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