Interface Design Models
15.2.1 Interface Design Models
Four different models come into play when a user interface is to be designed. The
WebRef
software engineer creates a design model, a human engineer (or the software engi- An excellent source of GUI
neer) establishes a user model, the end-user develops a mental image that is often design guidelines, methods, and references
called the user's model or the system perception, and the implementers of the system can be found at
create a system image [RUB88]. Unfortunately, each of these models may differ sig-
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nificantly. The role of interface designer is to reconcile these differences and derive
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a consistent representation of the interface.
A design model of the entire system incorporates data, architectural, interface, and procedural representations of the software. The requirements specification may
PA R T T H R E E C O N V E N T I O N A L M E T H O D S F O R S O F T WA R E E N G I N E E R I N G
establish certain constraints that help to define the user of the system, but the inter- face design is often only incidental to the design model. 1
The user model establishes the profile of end-users of the system. To build an effec- tive user interface, "all design should begin with an understanding of the intended users, including profiles of their age, sex, physical abilities, education, cultural or eth- nic background, motivation, goals and personality" [SHN90]. In addition, users can
be categorized as • Novices. No syntactic knowledge 2 of the system and little semantic
knowledge 3 of the application or computer usage in general. “USER, n.: The word
• Knowledgeable, intermittent users. Reasonable semantic knowledge of computer
the application but relatively low recall of syntactic information necessary to professionals use
when they mean use the interface. 'idiot.' “
• Knowledgeable, frequent users. Good semantic and syntactic knowledge
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that often leads to the "power-user syndrome"; that is, individuals who look for shortcuts and abbreviated modes of interaction.
The system perception (user's model) is the image of the system that end-users carry in their heads. For example, if the user of a particular word processor were asked to describe its operation, the system perception would guide the response. The accuracy of the description will depend upon the user's profile (e.g., novices would provide a sketchy response at best) and overall familiarity with software in the appli- cation domain. A user who understands word processors fully but has worked with the specific word processor only once might actually be able to provide a more com- plete description of its function than the novice who has spent weeks trying to learn the system.
The system image combines the outward manifestation of the computer-based system (the look and feel of the interface), coupled with all supporting information (books, manuals, videotapes, help files) that describe system syntax and semantics.
When the system When the system image and the system perception are coincident, users generally image and the system
feel comfortable with the software and use it effectively. To accomplish this "meld- perception coincide,
ing" of the models, the design model must have been developed to accommodate the the user can apply the
application effectively. information contained in the user model, and the system image must accurately reflect syntactic and semantic information about the interface.
The models described in this section are "abstractions of what the user is doing or thinks he is doing or what somebody else thinks he ought to be doing when he
1 Of course, this is not as it should be. For interactive systems, the interface design is as important as the data, architectural, or component-level design. 2 In this context, syntactic knowledge refers to the mechanics of interaction that is required to use the interface effectively. 3 Semantic knowledge refers to an underlying sense of the application—an understanding of the functions that are performed, the meaning of input and output, and the goals and objectives of the system.
F I G U R E 15.1
The user interface
Interface
User, task, and
design process
validation
environment analysis
Implementation
Interface design
uses an interactive system" [MON84]. In essence, these models enable the interface designer to satisfy a key element of the most important principle of user interface design: "Know the user, know the tasks."
Parts
» The Concurrent Development Model
» SUMMARY Software engineering is a discipline that integrates process, methods, and tools for
» PEOPLE In a study published by the IEEE [CUR88], the engineering vice presidents of three
» THE PROCESS The generic phases that characterize the software process—definition, development,
» THE PROJECT In order to manage a successful software project, we must understand what can go
» METRICS IN THE PROCESS AND PROJECT DOMAINS
» Extended Function Point Metrics
» METRICS FOR SOFTWARE QUALITY
» INTEGRATING METRICS WITHIN THE SOFTWARE PROCESS
» METRICS FOR SMALL ORGANIZATIONS
» ESTABLISHING A SOFTWARE METRICS PROGRAM
» Obtaining Information Necessary for Scope
» An Example of LOC-Based Estimation
» QUALITY CONCEPTS 1 It has been said that no two snowflakes are alike. Certainly when we watch snow
» SUMMARY Software quality assurance is an umbrella activity that is applied at each step in the
» R diagram 1.4 <part-of> data model; data model <part-of> design specification;
» SYSTEM MODELING Every computer-based system can be modeled as an information transform using an
» Facilitated Application Specification Techniques
» Data Objects, Attributes, and Relationships
» Entity/Relationship Diagrams
» Hatley and Pirbhai Extensions
» Creating an Entity/Relationship Diagram
» SUMMARY Design is the technical kernel of software engineering. During design, progressive
» Data Modeling, Data Structures, Databases, and the Data Warehouse
» Data Design at the Component Level
» A Brief Taxonomy of Styles and Patterns
» Quantitative Guidance for Architectural Design
» Isolate the transform center by specifying incoming and outgoing
» SUMMARY Software architecture provides a holistic view of the system to be built. It depicts the
» The User Interface Design Process
» Defining Interface Objects and Actions
» D E S I G N E VA L U AT I O N
» Testing for Real-Time Systems
» Organizing for Software Testing
» Criteria for Completion of Testing
» The Transition to a Quantitative View
» The Attributes of Effective Software Metrics
» Architectural Design Metrics
» Component-Level Design Metrics
» SUMMARY Software metrics provide a quantitative way to assess the quality of internal product
» Encapsulation, Inheritance, and Polymorphism
» Identifying Classes and Objects
» The Common Process Framework for OO
» OO Project Metrics and Estimation
» Event Identification with Use-Cases
» SUMMARY Object-oriented analysis methods enable a software engineer to model a problem by
» Partitioning the Analysis Model
» Designing Algorithms and Data Structures
» Program Components and Interfaces
» SUMMARY Object-oriented design translates the OOA model of the real world into an
» Testing Surface Structure and Deep Structure
» Deficiencies of Less Formal Approaches 1
» What Makes Cleanroom Different?
» Design Refinement and Verification
» SUMMARY Cleanroom software engineering is a formal approach to software development that
» Structural Modeling and Structure Points
» Describing Reusable Components
» SUMMARY Component-based software engineering offers inherent benefits in software quality,
» Guidelines for Distributing Application Subsystems
» Middleware and Object Request Broker Architectures
» An Overview of a Design Approach
» Consider expert Web developer will create a complete design, but time and cost can be appropriate
» A Software Reengineering Process Model
» Reverse Engineering to Understand Data
» Forward Engineering for Client/Server Architectures
» SUMMARY Reengineering occurs at two different levels of abstraction. At the business level,
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