S O F T WA R E D E S I G N A N D S O F T WA R E E N G I N E E R I N G Software design sits at the technical kernel of software engineering and is applied
13.1 S O F T WA R E D E S I G N A N D S O F T WA R E E N G I N E E R I N G Software design sits at the technical kernel of software engineering and is applied
regardless of the software process model that is used. Beginning once software require- ments have been analyzed and specified, software design is the first of three techni-
“The most common cal activities—design, code generation, and test—that are required to build and verify miracles of software
the software. Each activity transforms information in a manner that ultimately results engineering are the
in validated computer software. transitions from
Each of the elements of the analysis model (Chapter 12) provides information that analysis to design
and design to code.” is necessary to create the four design models required for a complete specification of
Richard Dué
design. The flow of information during software design is illustrated in Figure 13.1. Software requirements, manifested by the data, functional, and behavioral models, feed the design task. Using one of a number of design methods (discussed in later chapters), the design task produces a data design, an architectural design, an inter- face design, and a component design.
The data design transforms the information domain model created during analysis into the data structures that will be required to implement the software. The data objects and relationships defined in the entity relationship diagram and the detailed data content depicted in the data dictionary provide the basis for the data design activ- ity. Part of data design may occur in conjunction with the design of software archi- tecture. More detailed data design occurs as each software component is designed.
The architectural design defines the relationship between major structural elements of the software, the “design patterns” that can be used to achieve the requirements
CHAPTER 13
DESIGN CONCEPTS AND PRINCIPLES
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F I G U R E 13.1 Translating the analysis model into a software design that have been defined for the system, and the constraints that affect the way in which
architectural design patterns can be applied [SHA96]. The architectural design rep- resentation—the framework of a computer-based system—can be derived from the system specification, the analysis model, and the interaction of subsystems defined within the analysis model.
The interface design describes how the software communicates within itself, with systems that interoperate with it, and with humans who use it. An interface implies
a flow of information (e.g., data and/or control) and a specific type of behavior. There- fore, data and control flow diagrams provide much of the information required for interface design.
The component-level design transforms structural elements of the software archi- tecture into a procedural description of software components. Information obtained from the PSPEC, CSPEC, and STD serve as the basis for component design.
During design we make decisions that will ultimately affect the success of soft- ware construction and, as important, the ease with which software can be main- tained. But why is design so important?
The importance of software design can be stated with a single word—quality. Design is the place where quality is fostered in software engineering. Design pro- vides us with representations of software that can be assessed for quality. Design is the only way that we can accurately translate a customer's requirements into a fin- ished software product or system. Software design serves as the foundation for all
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
the software engineering and software support steps that follow. Without design, we risk building an unstable system—one that will fail when small changes are made; one that may be difficult to test; one whose quality cannot be assessed until late in the software process, when time is short and many dollars have already been spent.
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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