As a result, new software development approaches are evolved, as agile methodologies, mainly to solve such problem. The new methodologies include modifications to software development processes, to make them more productive and flexible. This paper has the following structure: Section 2 briefs the history of development approaches.
Section 3 explains the evolvement of software development towards agile methodologies, and presents the values and concepts of agile development. It also covers the main and most used agile methodologies. Section 4 describes the limitations to apply agile methodologies, and the last section concludes the paper. Programming started with structured languages as Fortran in [4], and then evolved to object- oriented languages in the s [15].
Similarly, software development approaches have evolved during time. A software development approach guides the developer through the software development process.
To develop software, the developers usually choose a. The first development approach came into existence after the software crisis in the s [13]. Software engineers tried to reduce the effect of the crisis and stop it by following structured methodologies for software development.
Using these methods, the number of failed or uncompleted software projects was reduced, the cost and development time of software projects were decreased, and the effect of the software crisis is limited [13]. They include not only the objects and object oriented principles, but also the best practices from structured methodologies [13].
At the early years of software development, most of the users requirements were fairly stable, and development followed the plans without major changes. However, as software development involved more critical and dynamic industrial projects, new difficulties emerged according to the growth of companies. These difficulties include [1][19]:. Evolving requirements: customer requirements are changing due to evolving business needs or legislative issues.
Most of the customers do not have a clear vision about the specifications of their requirements at the early stages. Some customers realize what their true requirements are only when they use an application that does not really meet their needs.
Another source of change comes from experiences gained during the development. Customer involvement: lack of customer involvement leads to higher chances of project failure. Many companies usually do not allocate any effort for customer involvement. Deadlines and budgets: often, customers do not accept failure.
On the other hand, companies usually. Miscommunications: one cause of the misunderstanding of requirements is the miscommunication between developers and customers. For example, each party uses its own jargon, and this leads to misunderstanding of customers needs. With the existence of such problems, the OO software development methodologies cannot satisfy the objectives of software development companies.
New development methodologies have to be applied in order to overcome these problems. A number of IT professionals started to work individually on new approaches to develop software.
The results of their researches were a set of new development methodologies that have many common features. When they met in in conference in Utah [1], they created the so called: Agile Manifesto.
These approaches were developed based on the same rule that the best way to verify a system is to deliver working versions to the customer, then update it according to their notes. Agile authors built their methodologies on four principles. First, the main objective is to develop software that satisfies the customers, through continuous delivering of working software, and getting feedback from customers about it.
The second principle is accepting changes in requirements at any development stage, so that customers would feel more comfortable with the development process. The third principle is the cooperation between the developers and the customers business people on a daily basis throughout the project development.
The last principle is developing on a test- driven basis; that is to write test prior to writing code. A test suite is run on the application after any code change [1]. Agility in short means to strip away as much of the heaviness, commonly associated with traditional software development methodologies, as possible, in order to promote quick response to changing environments, changes in user requirements, accelerate project deadlines, and the like [7].
Agile methodologies prefer software development over documentation. Their philosophy is to deliver many working versions of the. Applying this philosophy will help to overcome the problems mentioned earlier, by welcoming changes, satisfying user requirements, faster development, and at the end, users will have just the system they need. Extreme Programming was introduced by Kent Beck in Being an emerging agile methodology, XP offers a number of practices, values and principles which are advised to be adopted in order to run a software development project [3].
XP is a package of several practices and deas, most of which are not new. The combination and packaging of all of these is, however, new [11]. Extreme Programming was in fact targeted especially at small co-located teams developing non- critical products.
It has been suggested that the early adopters of agile methods have been small high-tech product companies [16]. Currently, however, it has already been proven at many companies of all different sizes and industries worldwide [8].
The main purpose is to deliver what the customer needs, at the time it is needed. In addition to this, one of the main reasons of its success is its ability to accept changes at anytime during the development. XP also emphasises teamwork; experiences from all stakeholders are employed to meet the specific goals, and within the given constraints [8]. Figure 1. The flow in a project using XP [8] This agile methodology improves software development in four ways.
Firstly, high communications between the developers and their customers. Second, the simplicity of design. Third, the continuous modification according customers feedback, by delivering a large number of working software to the customer. Fourth, encouraging the customer and developers to get to the correct requirements by the develop-feedback cycle [8]. Those four items are called XP values.
There are some programming principles that are encouraged by XP. One of them is that, simplicity and flexibility will reduce maintenance costs of the software in the future. Another programming practice is the intensive and robust testing mechanism, which will reduce the number of bugs reported later by the customer after delivering the final version of the application.
Embracing changes is also encouraged by XP, since customers are most likely to notice new opportunities for improving the system to meet their goals, while still in the development process. Moreover, XP encourages creating high quality code [8].
Many other rules and practices are provided by XP, for all the phases of software development. These include: creating user stories; making small frequent releases; dividing the project into iterations; creating spike solutions to reduce risk; availability of the customer; writing code to agreed standards; pair programming; leaving optimization until last; all the code is unit tested; creating a test case for each bug found; just to name a few [8][11]. However, XP is not best suited for any project.
There are some conditions that help to decide whether to apply the XP methodology for a software development project or not. Some projects have unclear or dynamic requirements, in such case XP will succeed, while other methodologies will fail. For projects with high risk that appear to be a new challenge for the developing company, XP practices can help to lower this risk, and increase the possibility of success.
On the other hand, XP is not best suited for companies with large teams; it works best for teams with 2 to 12 members. In subsequent sprints, the teams refine or enhance the model based on customer feedback—for example, by adjusting the safe following distance or altering the rates at which the vehicle accelerates or decelerates—and optimize it for code generation and deployment to the ECU. The generated code may be used as is or integrated with legacy code as part of a larger system. Results from all these activities are reported automatically to track progress and for stakeholders not using development tools.
In later sprints, the teams incorporate more rigorous verification and validation activities, including SIL, PIL, or HIL tests, to ensure that the design meets requirements. They also check that the models and code comply with established standards and guidelines, use static analysis and formal methods to prove the absence of critical run-time errors, and produce reports and other artifacts in preparation for standards certification.
As the project progresses, customer needs can shift. For example, the customer might request model predictive control rather than a classical control algorithm because an advanced MPC controller enables the vehicle to react to more aggressive maneuvers by other vehicles in the environment.
Because a system model is being used on this project, the algorithm team can easily replace the original control algorithm with a newly developed model predictive controller and leave the rest of the model unchanged. The team reruns the simulations and shares the results with the customer. An informed decision can then be made on whether to proceed with the design change or revert to the previous approach.
This team used Model-Based Design within their agile development workflow and delivered working software well before hardware was involved. Modeling and simulation enabled the team to continuously improve the design based on customer feedback, and even accommodate a significant requirement change late in the project. Agile Manifesto. Adaptive Cruise Control with Sensor Fusion. Select a Web Site. Choose a web site to get translated content where available and see local events and offers.
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Agile and Model-Based Design: The Basics Agile software development methods are built on the core values and principles outlined in the Agile Manifesto , published in Figure 1. Agile development using the Scrum framework. Mapping the Core Values of Agile to Model-Based Design The Agile Manifesto defines four core values for developing software: Individuals and interactions over processes and tools Working software over comprehensive documentation Customer collaboration over contract negotiation Responding to change over following a plan The manifesto authors point out that "over" does not mean "not".
Some analysts distinguish between upper and lower CASE tools. An upper CASE tool allows the analyst to create and modify the system design. All the information about the project is stored in an encyclopedia called the CASE repository, a large collection of records, elements, diagrams, screens, reports, and other information see figure below.
Analysis reports may be produced using the repository information to show where the design is incomplete or contains errors.
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