Model based design

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

The process of design (recall from L15) interviews ethnography what is there vs. what is wanted guidelines principles standards dialogue notations precise specification architectures documentation help evaluation heuristics scenarios task analysis what is wanted analysis design implement and deploy prototype

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

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

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

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

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.

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

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

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

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

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