Task Descriptions (Hierarchical Task Analysis)

A structured, objective approach to describing users’ performance of tasks, hierarchical task analysis originated in human factors. In its most basic form, a hierarchical task analysis provides an understanding of the tasks users need to perform to achieve certain goals. You can break down these tasks into multiple levels of sub tasks  In user experience, you can use hierarchical task analysis to describe the interactions between a user and a software system. When designing a new system, hierarchical task analysis lets you explore various possible approaches to completing the same task. When analyzing an existing system, it can help you to optimize particular interactions.

Applying Hierarchical Task Analysis to User Experience

Hierarchical task analysis requires a detailed understanding of users’ tasks. You can achieve this understanding by,

1. Identifying users’ primary goals
2. Detailing the steps users must perform to accomplish their goals
3. Optimizing these procedures

Example Hierarchical Task Analysis for ordering a book:

0.In order to borrow a book from the library 

1. go to the library 

2. find the required book

2.1 access library catalogue

2.2 access the search screen

2.3 enter search criteria

2.4 identify required book 

2.5 note location

3. go to correct shelf and retrieve book

4. take book to checkout counter

HTA Diagram

The Benefits of Hierarchical Task Analysis

Understanding user interactions at multiple levels of abstraction provides several benefits.

• It lets you objectively compare different approaches to the supporting same task—in terms of the numbers and types of steps the approaches require. For instance, reducing the number of steps in a task would probably enable a user to complete the task more rapidly, so replacing multiple fields with a single field would speed up the task. However, this would also make the address less easy to verify. The hierarchical task analysis provides a framework in which you can capture such a design rationale and refer to any related documentation.

• There may be several competing approaches to the same problem, so ensuring your team uses common language and a consistent approach to hierarchical task analysis can help you to compare them fairly.

• It enables effective UX design, because designers can understand how a system works, at whatever level of abstraction is most appropriate for what they are currently trying to accomplish.

• It supports UX design reuse. UX design patterns are a useful step toward UX design reuse, but they describe only the high?level principles of interactions. Hierarchical task analysis lets you capture multiple implementations of a design pattern—expressing interactions in a common structured format—and identify new design patterns.

But still there are some practical issues regarding HTA in real tasks.

1. Real tasks are very complex
2. Task analysis may not scale very well
3. Notation soon becomes awkward, difficult to follow
4. What would be to produce a task analysis with hundreds of tasks, sub-tasks?
5. It cannot model overlapping or parallel tasks