Entity/Relationship Diagrams
12.3.3 Entity/Relationship Diagrams
The primary purpose of The object/relationship pair (discussed in Section 12.3.1) is the cornerstone of the the ERD is to represent data model. These pairs can be represented graphically using the entity/relationship entities (data objects)
diagram. The ERD was originally proposed by Peter Chen [CHE77] for the design of and their relationships
with one another. relational database systems and has been extended by others. A set of primary com- ponents are identified for the ERD: data objects, attributes, relationships, and vari- ous type indicators. The primary purpose of the ERD is to represent data objects and their relationships.
Rudimentary ERD notation has already been introduced in Section 12.3. Data objects are represented by a labeled rectangle. Relationships are indicated with a labeled line connecting objects. In some variations of the ERD, the connecting line contains a diamond that is labeled with the relationship. Connections between data objects and relationships are established using a variety of special symbols that indi- cate cardinality and modality (Section 12.3.2).
The relationship between the data objects car and manufacturer would be rep- resented as shown in Figure 12.6. One manufacturer builds one or many cars. Given
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
F I G U R E 12.7
An expanded ERD
Contracts Transports
Shipper
the context implied by the ERD, the specification of the data object car (data object table in Figure 12.6) would be radically different from the earlier specification (Figure 12.3). By examining the symbols at the end of the connection line between objects, it can be seen that the modality of both occurrences is mandatory (the vertical lines).
Expanding the model, we represent a grossly oversimplified ERD (Figure 12.7) of the distribution element of the automobile business. New data objects, shipper and
Develop the ERD dealership, are introduced. In addition, new relationships—transports, contracts, iteratively by refining
both data objects and licenses, and stocks—indicate how the data objects shown in the figure associate with the relationships that
one another. Tables for each of the data objects contained in the ERD would have to connect them.
be developed according to the rules introduced earlier in this chapter. In addition to the basic ERD notation introduced in Figures 12.6 and 12.7, the ana- lyst can represent data object type hierarchies. In many instances, a data object may actually represent a class or category of information. For example, the data object car can be categorized as domestic, European, or Asian. The ERD notation shown in Figure 12.8 represents this categorization in the form of a hierarchy [ROS85].
ERD notation also provides a mechanism that represents the associativity between objects. An associative data object is represented as shown in Figure 12.9. In the fig- ure, each of the data objects that model the individual subsystems is associated with the data object car.
F I G U R E 12.8
Data object-
Car
type hierarchies
F I G U R E 12.9
Associative
Electronics
data objects
Drive train
Car
Data modeling and the entity relationship diagram provide the analyst with a con- cise notation for examining data within the context of a software application. In most cases, the data modeling approach is used to create one piece of the analysis model, but it can also be used for database design and to support any other requirements analysis methods.
12.4 F U N C T I O N A L M O D E L I N G A N D I N F O R M AT I O N F L O W
Information is transformed as it flows through a computer-based system. The system accepts input in a variety of forms; applies hardware, software, and human elements to transform it; and produces output in a variety of forms. Input may be a control
External entity
Input data
Intermediate Output data
Data store
Data store
Data store
Output data
Input data
External entity
F I G U R E 12.10
I nformation flow model
signal transmitted by a transducer, a series of numbers typed by a human operator,
a packet of information transmitted on a network link, or a voluminous data file retrieved from secondary storage. The transform(s) may comprise a single logical comparison, a complex numerical algorithm, or a rule-inference approach of an expert system. Output may light a single LED or produce a 200-page report. In effect, we can create a flow model for any computer-based system, regardless of size and complexity.
Structured analysis began as an information flow modeling technique. A com- puter-based system is represented as an information transform as shown in Figure
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,
Show more