Model based design

1. Model based design

2. Objective • The interactive system design consisting of several stages such as • Requirement Specification • Design • Prototyping • Evaluation • The interactive system design is highly iterative

3. scenariostask analysis guidelines principles standards precisespecification interviews ethnography what is there vs. what is wanted dialoguenotations evaluation heuristics architectures documentation help The process of design (recall from L15) what iswanted analysis design implement and deploy prototype

4. Objective • The iterative life cycle is • Time consuming and • Also requires cost (for coding and testing) • It is always good if we have an alternative method that reduces • Time, effort and cost required for the design life cycle • Model-based design provides one such alternative

5. Motivation • Suppose you are trying to design an interactive system • First, you should identify such as • Requirements (“Know the user”) • Contextual Inquiry • Which are time and cost consuming and tedious process • Instead of going through the process, it would have been better if we have a “model of the user” • Which is known as model based design

6. Idea of a model • A ‘model’ in HCI refers to • “A representation of the user’s interaction behavior under certain assumptions” • The representation is typically obtained form extensive empirical studies • Collecting and analyzing data from end users • The model represents behavior of average users, not individuals • It saves lots of time, cost and effort

7. Types of model • 1. Descriptive/ prescriptive models • It describe user behavior during interaction in qualitative terms. • An example is the Norman’s model of interaction • These models help in formulating (prescribing) guidelines for interface design

8. Types of model • 2. Predictive engineering models: • These models can “predict” behavior of a user in quantitative terms. • An example is the GOMS model (to be discussed later in this module) • GOMS model can predict the task completion time of an average user for a given system.

9. Predictive engineering models • The predictive engineering models used in HCI are of three types • Formal (system) model • Cognitive (user) model • Syndetic (hybrid) model

10. Predictive engineering models • Formal (system) models • The interactive system is represented using ‘formal specification’ techniques • For ex: ‘state transition networks’/’system state space’ • Cognitive (user) models • These models capture the user’s thought (cognitive) process during interaction • For ex: A GOMS model tells us the series of cognitive steps involved in typing a word • Syndetic (hybrid) model • Complex and rarely used

11. Model based design limitations • The models can not capture individual user characteristics • It only models average user behavior

12. Summary • Model-based design reduce the need for real users in interactive system • However, they can not completely eliminate the role played by real users • It can be employed in the initial design stages

13. Descriptive/ prescriptive models: Donald Norman’s model • Seven stages • user establishes the goal • formulates intention • specifies actions at interface • executes action • perceives system state • interprets system state • evaluates system state with respect to goal • Norman’s model concentrates on user’s view of the interface