Content (3.2.2) - Model-based Design - Human Computer Interaction (HCI) Micro Specialization
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GOMS: Goals and Operators - Defining User Intent and Actions

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Chapter Content

The GOMS model, standing for Goals, Operators, Methods, and Selection Rules, provides a sophisticated, hierarchical framework for understanding how expert users interact with complex systems. It builds upon the foundational concept of operators, as seen in KLM, but embeds them within a richer structure of user knowledge and decision-making.
The first component, Goals (G), represents the user's overarching objectives or intentions. These are declarative statements of "what" the user wants to achieve. For instance, a user might have the goal to "Send Email" or "Delete Word." Goals are not static; they can be decomposed into hierarchical sub-goals. So, "Print Document" might involve sub-goals like "Select Printer," "Set Print Options," and "Send to Printer." This hierarchy mirrors the way complex tasks are mentally broken down into simpler, manageable steps.
The second component, Operators (O), are the atomic actions that users perform, or that the system performs in response, to work towards these goals. Operators are the indivisible building blocks of interaction within the GOMS model. These can be categorized into:
* Internal Operators: These are cognitive or perceptual actions, such as "Read Text," "Recall Command," or "Mental Preparation."
* External Operators: These are observable motor actions, like "Type Character," "Click Mouse," or "Press Button."
* System Operators: These represent system responses, such as "System Response Time" or "Screen Redraw."
While KLM primarily focused on a specific set of motor and general mental operators, GOMS allows for a much richer and context-specific set of operators, providing greater flexibility to model diverse interactions.

Chunk 2: Methods and Selection Rules - The "How" and The "Choice"

  • Chunk Title: GOMS: Methods and Selection Rules - Strategies and Decisions
  • Chunk Text: Building on goals and operators, the third and fourth components of GOMS illuminate how expert users achieve their objectives and make choices.
    Methods (M) are well-learned, pre-defined sequences of operators and sub-goals that an expert user employs to achieve a specific goal. They represent the "how-to" knowledge – the optimized procedures that an experienced user has acquired through practice. For example, to achieve the GOAL: Delete-Word, an expert might know Method 1: Mouse-Select-and-Menu-Delete (involving moving the mouse, dragging, clicking menus) or Method 2: Keyboard-Shortcut-Delete (involving pressing Ctrl+Shift+Arrow, then Delete). A single goal can often be achieved by multiple different methods, reflecting the flexibility offered by an interface or the user's diverse knowledge base.
    Finally, Selection Rules (S) are the "if-then" rules that an expert user applies to choose among multiple available methods for achieving a given goal. These rules model the expert user's decision-making process, based on factors like efficiency, current context, system state, or personal preference. For instance, a GOAL: Save-File might have a selection rule: "IF mouse is currently on menu bar THEN use Method: Menu-Save ELSE IF user prefers keyboard shortcuts THEN use Method: Keyboard-Save ELSE use Method: Toolbar-Icon-Save." Selection rules are critical for predicting which path an expert user will take in a dynamic interaction, providing deeper insight into their cognitive strategy beyond just a linear sequence of actions. Together, Goals, Operators, Methods, and Selection Rules provide a powerful, hierarchical framework for thoroughly analyzing and predicting expert user performance in complex, routine tasks.

Glossary

  • Goals (G): High-level objectives or intentions a user desires to achieve. Can be broken down into sub-goals.
  • Operators (O): Basic, atomic perceptual, cognitive, and motor actions performed by user or system. The building blocks of interaction.
  • Methods (M): A well-learned, practiced sequence of operators and sub-goals used to achieve a specific goal; the "how-to."
  • Selection Rules (S): "If-then" rules that specify which method to choose when multiple methods are available for a goal, based on context or user preference.
  • Hierarchical Representation: GOMS's structure where goals can contain sub-goals, and methods combine operators and sub-goals.
  • Explicit Cognitive Modeling: GOMS's ability to represent the user's internal thought processes and decision-making, not just observable actions.

Estimated Study Time

1 hour 30 minutes

Reference Links

  1. Card, S. K., Moran, T. P., & Newell, A. (1983). The Psychology of Human-Computer Interaction. (This is the foundational text for GOMS and KLM. While not freely online, it's the primary reference.)
  2. Jakob Nielsen's Alertbox (The GOMS Model): https://www.nngroup.com/articles/goms-model/ - A good, accessible overview of GOMS.
  3. Human-Computer Interaction (Dix et al.) Chapter 13 (Model-based Evaluation): (Look for sections on GOMS in standard HCI textbooks. Check a library or academic resource.)
  4. Wikipedia (GOMS): https://en.wikipedia.org/wiki/GOMS - Provides a good summary and links to further reading.

Key Concepts

  • Hierarchy: GOMS explicitly models goals and sub-goals, reflecting how complex tasks are broken down.
  • Expert Knowledge: GOMS represents the knowledge an expert user possesses (goals, methods, selection rules) and how they apply it through operators.
  • Explicit Decision-Making: Selection Rules are a key differentiator, formalizing how experts choose among alternatives.
  • Beyond Pure Timing: While predicting time, GOMS also offers insight into the structure of interaction and cognitive strategy.

Examples

  • Goals: A user's GOAL: Prepare-Presentation might involve GOAL: Insert-Image, GOAL: Format-Text, GOAL: Add-Transitions.
  • Operators: MoveMouse(to_Save_button), PressKey(Alt), Scan_Screen_for_Error_Message, Recognize_Icon.
  • Methods: For GOAL: Print-Document, an expert might have Method: Print-via-File-Menu or Method: Print-via-Ctrl-P. Each method is a distinct sequence of operators and sub-goals.
  • Selection Rules: "IF I am focused on the keyboard THEN use Method: Ctrl-S ELSE IF I am using the mouse THEN use Method: Click-Save-Icon." This rule dictates the choice based on the user's current hand position or preference.

Flashcards

  • Term: GOMS Model
    Definition: A hierarchical cognitive model describing Goals, Operators, Methods, and Selection Rules for expert user performance.
  • Term: Goal (G)
    Definition: A user's desired objective or intention (e.g., GOAL: Send-Email).
  • Term: Operator (O)
    Definition: Basic perceptual, cognitive, or motor actions performed by user or system (e.g., Type-Character, Mental-Prep).
  • Term: Method (M)
    Definition: A well-learned sequence of operators and sub-goals to achieve a goal (the "how-to").
  • Term: Selection Rule (S)
    Definition: An "if-then" rule dictating which method to choose when multiple are available for a goal.

Memory Aids

  • GOMS Acronym: Goals (what), Operators (do), Methods (how), Selection (choose).
  • "G is your destination, O is your steps, M is your route, S is your traffic light.": Analogizing GOMS components to navigating a journey.
  • "KLM is a line, GOMS is a tree.": Helps visualize the difference in structure (linear vs. hierarchical).

Detailed Explanation

No detailed explanation available.

Examples & Analogies

No real-life example available.

Key Concepts

  • Hierarchy: GOMS explicitly models goals and sub-goals, reflecting how complex tasks are broken down.

  • Expert Knowledge: GOMS represents the knowledge an expert user possesses (goals, methods, selection rules) and how they apply it through operators.

  • Explicit Decision-Making: Selection Rules are a key differentiator, formalizing how experts choose among alternatives.

  • Beyond Pure Timing: While predicting time, GOMS also offers insight into the structure of interaction and cognitive strategy.

  • Examples

  • Goals: A user's GOAL: Prepare-Presentation might involve GOAL: Insert-Image, GOAL: Format-Text, GOAL: Add-Transitions.

  • Operators: MoveMouse(to_Save_button), PressKey(Alt), Scan_Screen_for_Error_Message, Recognize_Icon.

  • Methods: For GOAL: Print-Document, an expert might have Method: Print-via-File-Menu or Method: Print-via-Ctrl-P. Each method is a distinct sequence of operators and sub-goals.

  • Selection Rules: "IF I am focused on the keyboard THEN use Method: Ctrl-S ELSE IF I am using the mouse THEN use Method: Click-Save-Icon." This rule dictates the choice based on the user's current hand position or preference.

  • Flashcards

  • Term: GOMS Model

  • Definition: A hierarchical cognitive model describing Goals, Operators, Methods, and Selection Rules for expert user performance.

  • Term: Goal (G)

  • Definition: A user's desired objective or intention (e.g., GOAL: Send-Email).

  • Term: Operator (O)

  • Definition: Basic perceptual, cognitive, or motor actions performed by user or system (e.g., Type-Character, Mental-Prep).

  • Term: Method (M)

  • Definition: A well-learned sequence of operators and sub-goals to achieve a goal (the "how-to").

  • Term: Selection Rule (S)

  • Definition: An "if-then" rule dictating which method to choose when multiple are available for a goal.

  • Memory Aids

  • GOMS Acronym: Goals (what), Operators (do), Methods (how), Selection (choose).

  • "G is your destination, O is your steps, M is your route, S is your traffic light.": Analogizing GOMS components to navigating a journey.

  • "KLM is a line, GOMS is a tree.": Helps visualize the difference in structure (linear vs. hierarchical).

Examples & Applications

Goals: A user's GOAL: Prepare-Presentation might involve GOAL: Insert-Image, GOAL: Format-Text, GOAL: Add-Transitions.

Operators: MoveMouse(to_Save_button), PressKey(Alt), Scan_Screen_for_Error_Message, Recognize_Icon.

Methods: For GOAL: Print-Document, an expert might have Method: Print-via-File-Menu or Method: Print-via-Ctrl-P. Each method is a distinct sequence of operators and sub-goals.

Selection Rules: "IF I am focused on the keyboard THEN use Method: Ctrl-S ELSE IF I am using the mouse THEN use Method: Click-Save-Icon." This rule dictates the choice based on the user's current hand position or preference.

Flashcards

Term: GOMS Model

Definition: A hierarchical cognitive model describing Goals, Operators, Methods, and Selection Rules for expert user performance.

Term: Goal (G)

Definition: A user's desired objective or intention (e.g., GOAL: Send-Email).

Term: Operator (O)

Definition: Basic perceptual, cognitive, or motor actions performed by user or system (e.g., Type-Character, Mental-Prep).

Term: Method (M)

Definition: A well-learned sequence of operators and sub-goals to achieve a goal (the "how-to").

Term: Selection Rule (S)

Definition: An "if-then" rule dictating which method to choose when multiple are available for a goal.

Memory Aids

GOMS Acronym: Goals (what), Operators (do), Methods (how), Selection (choose).

"G is your destination, O is your steps, M is your route, S is your traffic light.": Analogizing GOMS components to navigating a journey.

"KLM is a line, GOMS is a tree.": Helps visualize the difference in structure (linear vs. hierarchical).

Memory Aids

Interactive tools to help you remember key concepts

🧠

Memory Tools

Goals (what), Operators (do), Methods (how), Selection (choose).
* "G is your destination, O is your steps, M is your route, S is your traffic light."

🧠

Memory Tools

Helps visualize the difference in structure (linear vs. hierarchical).

Flash Cards

Glossary

Explicit Cognitive Modeling

GOMS's ability to represent the user's internal thought processes and decision-making, not just observable actions.

Wikipedia (GOMS)

https://en.wikipedia.org/wiki/GOMS - Provides a good summary and links to further reading.

Beyond Pure Timing

While predicting time, GOMS also offers insight into the structure of interaction and cognitive strategy.

Selection Rules

"IF I am focused on the keyboard THEN use Method: Ctrl-S ELSE IF I am using the mouse THEN use Method: Click-Save-Icon." This rule dictates the choice based on the user's current hand position or preference.

Definition

An "if-then" rule dictating which method to choose when multiple are available for a goal.

GOMS Acronym

Goals (what), Operators (do), Methods (how), Selection (choose).

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