第9章ソフトウェア工学

Several popular software process models in use today align with the Agile guidelines. While the phases used within Agile process models are similar to that of other models, the difference is that some disciplines in various phases may overlap. For example, in the Agile process model, all the requirements do not need to be defined in the inception phase prior to starting the design or to coding disciplines in the elaboration and construction phases. New requirements or changes in requirements can be considered as part of subsequent phases. Additionally, an incremental, iterative approach is applied, so that it is not necessary for all the functionality in one increment to be dealt with at once. It is worth noting that the incremental model that was presented earlier may be agile for a similar reason. The benefits of Agile process models are they are flexible (i.e., allow for changes along the way) and emphasize collaboration. They also allow for continuous improvement, which is advantageous if requirements are likely to change or needs are likely to evolve. The drawbacks are that Agile models can be difficult to scale.

Agile principles were formulated in the Agile Manifesto that was a response to the unsatisfying number of projects that were delayed, overrun their budget, and did not meet customers’ expectations. Agility refers to the ability to create and respond to change in order to profit in a turbulent business environment. Some Agile principles are as follows:

• Satisfy the customer through early and continuous delivery of software.

• Welcome changing requirements, even late in development.

• Deliver working software frequently, such as each couple of weeks.

• The most effective way of communication within a development team is face-to-face (via collaboration tools).

• Working software is the primary measure of progress.

• Maintain a sustainable working pace.

• Continuous attention to technical excellence and good design enhances agility.

• Simplicity—the art of maximizing the amount of work not done—is essential.

• The best architectures, requirements, and designs emerge from self-organizing teams.

The approaches that complement Agile software development are Scrum, DevOps, and Site Reliability Engineering.

To learn more about Agile, you can visit the Agile Alliance to learn the core principles of Agile development from the experts. The Agile Alliance is a global nonprofit organization that is focused on applying and expanding Agile values, principles, and practices. You can view its tutorial What is Agile? (https://openstax.org/r/76Agile) online, which provides more details on Agile and its use.

Scrum is a type of Agile software development model. The fundamental unit of Scrum is a Scrum team, which is typically ten or fewer people. It consists of one Scrum master, one product owner, and several developers. The Scrum master is responsible for running Scrum and for helping everyone understand its theory and practice. The product owner is responsible for product backlog management, which includes product goals and product backlog items. The product goal describes future desired features of the product, and the product backlog item defines what is required to be added to the product.

The product is developed in iterations called a sprint, which is a fixed-length event typically of one to four weeks. Each sprint starts with sprint planning, in which the team selects the product goals and product backlog items that will be implemented in that sprint. The selected product goals and product backlog items are moved to the sprint backlog, which is a plan for the current sprint. During the sprint, developers have a daily scrum, which is a 15-minute event for the developers that is held every day at the same time and the same place. During the daily scrum, the developers inspect the progress and, if needed, they adapt the objectives of the sprint. At the end of sprint, there is a sprint review, during which the Scrum team and stakeholders review a demonstration of what was achieved as part of the sprint increment, and the Scrum team gets feedback. After that, in the sprint retrospective, the Scrum team discusses what worked well and what worked poorly process-wise during the last sprint to produce the product increment and proposes changes to increase effectiveness. Figure 9.14 depicts the Scrum process.

The benefits of the Scrum framework include better quality of the product, decreased time to market, higher customer satisfaction, and increased collaboration within the development team. The drawbacks are that the approach requires training; it is not suitable for large teams; and it requires daily meetings.