Chapter 7 Implementation Issues - Software Engineering PDF

Implementation issues 30/10/2014 Chapter 7 Design and Implementat 1 ion Implementation issues  Focus here is not on programming, although this is obviously important, but on other implementation issues that are often not covered in programming texts:  Reuse Most mode...

Implementation issues 30/10/2014 Chapter 7 Design and Implementat 1 ion Implementation issues  Focus here is not on programming, although this is obviously important, but on other implementation issues that are often not covered in programming texts:  Reuse Most modern software is constructed by reusing existing components or systems. When you are developing software, you should make as much use as possible of existing code.  Configuration management During the development process, you have to keep track of the many different versions of each software component in a configuration management system.  Host-target development Production software does not usually execute on the same computer as the software development environment. Rather, you develop it on one computer (the host system) and execute it on a separate computer (the target system). 30/10/2014 Chapter 7 Design and Implementat 2 ion Reuse  From the 1960s to the 1990s, most new software was developed from scratch, by writing all code in a high-level programming language.  The only significant reuse or software was the reuse of functions and objects in programming language libraries.  Costs and schedule pressure mean that this approach became increasingly unviable, especially for commercial and Internet-based systems.  An approach to development based around the reuse of existing software emerged and is now generally used for business and scientific software. 30/10/2014 Chapter 7 Design and Implementat 3 ion Reuse levels  The abstraction level  At this level, you don’t reuse software directly but use knowledge of successful abstractions in the design of your software.  The object level  At this level, you directly reuse objects from a library rather than writing the code yourself.  The component level  Components are collections of objects and object classes that you reuse in application systems.  The system level  At this level, you reuse entire application systems. 30/10/2014 Chapter 7 Design and Implementat 4 ion Software reuse 30/10/2014 Chapter 7 Design and Implementat 5 ion Reuse costs  The costs of the time spent in looking for software to reuse and assessing whether or not it meets your needs.  Where applicable, the costs of buying the reusable software. For large off-the-shelf systems, these costs can be very high.  The costs of adapting and configuring the reusable software components or systems to reflect the requirements of the system that you are developing.  The costs of integrating reusable software elements with each other (if you are using software from different sources) and with the new code that you have developed. 30/10/2014 Chapter 7 Design and Implementat 6 ion Configuration management  Configuration management is the name given to the general process of managing a changing software system.  The aim of configuration management is to support the system integration process so that all developers can access the project code and documents in a controlled way, find out what changes have been made, and compile and link components to create a system.  See also Chapter 25. 30/10/2014 Chapter 7 Design and Implementat 7 ion Configuration management activities  Version management, where support is provided to keep track of the different versions of software components. Version management systems include facilities to coordinate development by several programmers.  System integration, where support is provided to help developers define what versions of components are used to create each version of a system. This description is then used to build a system automatically by compiling and linking the required components.  Problem tracking, where support is provided to allow users to report bugs and other problems, and to allow all developers to see who is working on these problems and when they are fixed. 30/10/2014 Chapter 7 Design and Implementat 8 ion Configuration management tool interaction 30/10/2014 Chapter 7 Design and Implementat 9 ion Host-target development  Most software is developed on one computer (the host), but runs on a separate machine (the target).  More generally, we can talk about a development platform and an execution platform.  A platform is more than just hardware.  It includes the installed operating system plus other supporting software such as a database management system or, for development platforms, an interactive development environment.  Development platform usually has different installed software than execution platform; these platforms may have different architectures. 30/10/2014 Chapter 7 Design and Implementat 10 ion Host-target development 30/10/2014 Chapter 7 Design and Implementat 11 ion Development platform tools  An integrated compiler and syntax-directed editing system that allows you to create, edit and compile code.  A language debugging system.  Graphical editing tools, such as tools to edit UML models.  Testing tools, such as Junit that can automatically run a set of tests on a new version of a program.  Project support tools that help you organize the code for different development projects. 30/10/2014 Chapter 7 Design and Implementat 12 ion Integrated development environments (IDEs)  Software development tools are often grouped to create an integrated development environment (IDE).  An IDE is a set of software tools that supports different aspects of software development, within some common framework and user interface.  IDEs are created to support development in a specific programming language such as Java. The language IDE may be developed specially, or may be an instantiation of a general-purpose IDE, with specific language-support tools. 30/10/2014 Chapter 7 Design and Implementat 13 ion  Component/system deployment factors  If a component is designed for a specific hardware architecture, or relies on some other software system, it must obviously be deployed on a platform that provides the required hardware and software support.  High availability systems may require components to be deployed on more than one platform. This means that, in the event of platform failure, an alternative implementation of the component is available.  If there is a high level of communications traffic between components, it usually makes sense to deploy them on the same platform or on platforms that are physically close to one other. This reduces the delay between the time a message is sent by one component and received by another. 30/10/2014 Chapter 7 Design and Implementat 14 ion  Open source development 30/10/2014 Chapter 7 Design and Implementat 15 ion Open source development  Open source development is an approach to software development in which the source code of a software system is published and volunteers are invited to participate in the development process  Its roots are in the Free Software Foundation (www.fsf.org), which advocates that source code should not be proprietary but rather should always be available for users to examine and modify as they wish.  Open source software extended this idea by using the Internet to recruit a much larger population of volunteer developers. Many of them are also users of the code. 30/10/2014 Chapter 7 Design and Implementat 16 ion Open source systems  The best-known open source product is, of course, the Linux operating system which is widely used as a server system and, increasingly, as a desktop environment.  Other important open source products are Java, the Apache web server and the mySQL database management system. 30/10/2014 Chapter 7 Design and Implementat 17 ion Open source issues  Should the product that is being developed make use of open source components?  Should an open source approach be used for the software’s development? 30/10/2014 Chapter 7 Design and Implementat 18 ion Open source business  More and more product companies are using an open source approach to development.  Their business model is not reliant on selling a software product but on selling support for that product.  They believe that involving the open source community will allow software to be developed more cheaply, more quickly and will create a community of users for the software. 30/10/2014 Chapter 7 Design and Implementat 19 ion Open source licensing  A fundamental principle of open-source development is that source code should be freely available, this does not mean that anyone can do as they wish with that code.  Legally, the developer of the code (either a company or an individual) still owns the code. They can place restrictions on how it is used by including legally binding conditions in an open source software license.  Some open source developers believe that if an open source component is used to develop a new system, then that system should also be open source.  Others are willing to allow their code to be used without this restriction. The developed systems may be proprietary and sold as closed source systems. 30/10/2014 Chapter 7 Design and Implementat 20 ion License models  The GNU General Public License (GPL). This is a so-called ‘reciprocal’ license that means that if you use open source software that is licensed under the GPL license, then you must make that software open source.  The GNU Lesser General Public License (LGPL) is a variant of the GPL license where you can write components that link to open source code without having to publish the source of these components.  The Berkley Standard Distribution (BSD) License. This is a non-reciprocal license, which means you are not obliged to re- publish any changes or modifications made to open source code. You can include the code in proprietary systems that are sold. 30/10/2014 Chapter 7 Design and Implementat 21 ion License management  Establish a system for maintaining information about open-source components that are downloaded and used.  Be aware of the different types of licenses and understand how a component is licensed before it is used.  Be aware of evolution pathways for components.  Educate people about open source.  Have auditing systems in place.  Participate in the open source community. 30/10/2014 Chapter 7 Design and Implementat 22 ion Key points  Software design and implementation are inter-leaved activities. The level of detail in the design depends on the type of system and whether you are using a plan-driven or agile approach.  The process of object-oriented design includes activities to design the system architecture, identify objects in the system, describe the design using different object models and document the component interfaces.  A range of different models may be produced during an object- oriented design process. These include static models (class models, generalization models, association models) and dynamic models (sequence models, state machine models).  Component interfaces must be defined precisely so that other objects can use them. A UML interface stereotype may be used to define interfaces. 30/10/2014 Chapter 7 Design and Implementat 23 ion Key points  When developing software, you should always consider the possibility of reusing existing software, either as components, services or complete systems.  Configuration management is the process of managing changes to an evolving software system. It is essential when a team of people are cooperating to develop software.  Most software development is host-target development. You use an IDE on a host machine to develop the software, which is transferred to a target machine for execution.  Open source development involves making the source code of a system publicly available. This means that many people can propose changes and improvements to the software. 30/10/2014 Chapter 7 Design and Implementat 24 ion