fundamentals of object oriented design in UML

Design and Implementation and fundamentals of object-oriented design in uml pdf
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Dr.ShaneMatts,United States,Teacher
Published Date:23-07-2017
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Chapter 7 Design and Implementation Chapter 7 Design and Implementation Slide 1 Topics covered  Object-oriented design using the UML  Design patterns  Implementation issues • Reuse • Configuration management • Host-target development  Open source development • Development issues and business model • License models Chapter 7 Design and Implementation Slide 2 What is “design and implementation”?  The stage in the software engineering process at which an executable software system is developed.  Design and implementation activities are invariably interleaved. • Software design is a creative activity in which you identify software components and their relationships, based on a customer’s requirements. • Implementation is the process of realizing the design as one or more executable programs. Chapter 7 Design and Implementation Slide 3 Build or buy?  In a wide range of domains, it is now possible to buy off-the-shelf systems (COTS) that can be adapted and tailored to users’ requirements. • For example, if a medical records system is required, you can buy a package that is already used in hospitals. This can be cheaper and faster than developing a system.  When you procure an application in this way, the design process becomes concerned with how to use the configuration features of that system to deliver the system requirements. Chapter 7 Design and Implementation Slide 4 Object-oriented design using the UML Chapter 7 Design and Implementation Slide 5 An object-oriented design process…  Structured, object-oriented design processes involve developing a number of different system models.  They require a lot of effort for development and maintenance, and for small systems, this may not be cost-effective.  However, for large systems developed by different groups, system models are an important communication mechanism. acknowledgment of both agile and planned-based principles Chapter 7 Design and Implementation Slide 6 ...an iterative, boot-strapping process Chapter 7 Design and Implementation Slide 7 Process stages  There are a variety of different object-oriented design processes.  But the common activities normally include: 1. Define the context and modes of use of the system. 2. Design the system architecture. 3. Identify the principal system objects. 4. Develop design models (static and dynamic). 5. Specify object interfaces.  The process illustrated here is for the wilderness weather station. (See Section 1.3.3, p. 22.) Chapter 7 Design and Implementation Slide 8 System context and interactions  Goal: develop an understanding of the relation- ships between the software being designed and its external environment.  Understanding of the system context also lets you establish the boundaries (scope) of the system.  This helps in deciding what features will be imple- mented in the system being designed and what features will be in associated systems. Chapter 7 Design and Implementation Slide 9 Context and interaction models  A system context model is a structural model that identifies the other systems in the environment of the system being developed.  An interaction model is a dynamic model that shows how the system interacts with its environment as it is used. Chapter 7 Design and Implementation Slide 10 Context model for the weather station (cardinality info) Chapter 7 Design and Implementation Slide 11 Interaction model based on Use Cases Chapter 7 Design and Implementation Slide 12 Use case description—Report weather System Weather station Use case Report weather Actors Weather information system, Weather station Description The weather station sends a summary of the weather data that has been collected from the instruments in the collection period to the weather information system. The data sent are the maximum, minimum, and average ground and air temperatures; the maximum, minimum, and average air pressures; the maximum, minimum, and average wind speeds; the total rainfall; and the wind direction as sampled at five- minute intervals. Stimulus The weather information system establishes a satellite communication link with the weather station and requests transmission of the data. Response The summarized data is sent to the weather information system. Comments Weather stations are usually asked to report once per hour but this frequency may differ from one station to another and may be modified in the future. Chapter 7 Design and Implementation Slide 13 Architectural design  Once interactions between the system and its environ- ment have been understood, this info is used in designing the system architecture.  Identify the major components that make up the system and their interactions, and then organize the components using an architectural pattern such as a layered or client- server model.  The weather station is comprised of independent subsystems that communicate by broadcasting messages via a shared infrastructure (another common architectural style in addition to those described in Chapter 6)... Chapter 7 Design and Implementation Slide 14 † High-level architecture of weather station † OO sub-system design model using UML “packages” Chapter 7 Design and Implementation Slide 15 Object class identification  Identifying object classes is often a difficult part of OO design.  There is no “magic formula” – it relies on the skill, experience, and domain knowledge of system designers  An iterative, boot-strapping process – you are unlikely to get it right the first time. Chapter 7 Design and Implementation Slide 16 Approaches to object identification  Use a grammatical approach based on a natural language description of the system (Abbott’s heuristic).  Associate objects with tangible things in the application domain (e.g., devices).  Use a behavioural approach: identify objects based on what participates in what behaviour. (cont’d) Chapter 7 Design and Implementation Slide 17 Approaches to object identification (cont.)  Use scenario-based analysis. The objects, attributes and methods associated with each scenario are identified.  Use an information-hiding based approach. Identify potentially changeable design decisions and isolate these in separate objects to minimize the impact of change. (Parnas) “Bonus” approach (No extra charge.) Chapter 7 Design and Implementation Slide 18 Weather station description A weather station is a package of software controlled instruments which collects data, performs some data processing and transmits this data for further processing. The instruments include air and ground thermometers, an anemometer, a wind vane, a barometer and a rain gauge. Data is collected every five minutes. (cont’d) Chapter 7 Design and Implementation Slide 19 Weather station description (cont’d) When a command is issued to transmit the weather data, the weather station processes and summarises the collected data. The summarized data is transmitted to the mapping computer when a request is received. Chapter 7 Design and Implementation Slide 20

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