第9章ソフトウェア工学

Imagine the life of a software engineer developing programs in the 1980s, which required typing programs on a terminal and printing punch cards that were fed into a mainframe computer! The world of software development is constantly evolving, and the platforms where software runs change rapidly, too. Software engineers need to stay up-to-date on current platforms and also become aware of what is coming next.

Can you imagine using a computer without a mouse or a graphical interface? Let us take a look at the way software platforms have evolved over time:

• Early Days (1980s): Mainframes and minicomputers were giant, even room-sized, and software was often run from the command line.

• The Rise of the Desktop (1990s): Welcome to the age of Windows and Mac! Graphical interfaces made computers more user-friendly, and client-server systems allowed applications to run across multiple machines.

• The Web Takes Over (2000s): The Internet exploded, and Java and C# became popular languages for building web applications.

• Mobile Mania (2010s): Smartphones like the iPhone changed the game. Software development focused on mobile apps that took advantage of constant connectivity.

Augmented and virtual reality (AR/VR), machine learning (ML), artificial intelligence (AI), the Internet of Things (IoT), and blockchain are some emerging technologies that are shaping up the future of Metaverse software platforms. Who knows what exciting new platforms await? Curious and adaptable software engineers will be best positioned to thrive in this ever-changing landscape.

Software is developed based on requirements, which are categorized as functional and nonfunctional, as shown in Figure 9.2. Functional requirements state what the software needs to do in terms of tangible functionality, such as the login or registration functionality that allows users to access a given piece of software such as their Facebook account. Nonfunctional requirements are measurable qualities of a piece of software, such as usability, performance, and other quality aspects.

As noted earlier, a functional requirement relates to the services the system provides to the users. It reflects the user’s expectation about the inherent characteristics of the software, (i.e., the functions it must perform). Functional requirements can include those phenomena that are generally seen or done when using a software solution, such as the information that is entered or that is generated by the software, the authenticating rules for using the software, or whether there should be an audible alert (such as a beep) when an action is selected. A nonfunctional requirement describes a desired quality or feature (i.e., constraint) and covers aspects of the software such as flexibility, maintainability, performance, portability, reliability, scalability, security, and more. For example, a nonfunctional requirement could specify that responses from the software must occur within a specific time frame, or that a software system must be able to handle a certain number of transactions at any given time. Another example of a constraint that a nonfunctional requirement may express is the need to use a specific programming language or follow a particular standard.

Nonfunctional features are sometimes categorized in terms of static or dynamic qualities. A static quality is a nonfunctional feature that is unchangeable and thus might be associated, for example, with the source code and related documentation, or with legal or project-environment specific requirements. A dynamic quality is a nonfunctional feature that relates to the qualitative behavior of software while it is in use, which means that is also depends on the hardware that the system runs on. Both quality types are measurable features rather than functions that are present or absent. Examples of static qualities include:

• maintainability, which is a measure of the amount of work required to fix bugs, improve performance, and keep the system running

• extensibility, which is a measure of the amount of work and cost of adding new features to software

• flexibility, which is a measure of the difficulty of updating the system to meet changing requirements

• portability, which is a measure of the amount of work and cost of migrating software solutions

• usability, which is a measure of how intuitive the user interface is

Examples of dynamic qualities are:

• performance, which is a measurement of how quickly the system responds to requests it receives

• throughput, which is a measure of how much input the system can process within a given time frame

• availability, which is a measure of how often the system will be ready and active for users

• scalability, which is the measurement of the work and cost to increase a system’s throughput

• security, which is a measure of confidence that data is protected from unauthorized disclosure and that systems are protected from unauthorized access

The relative importance of the preceding characteristics depends on the solution requirements and the environment in which they are to be used. For example, in an Internet banking application, availability and usability are typically key features advertised to customers. Security would also be important, as the software solution would need to comply with regulatory requirements. In a brokerage system, performance would be an important requirement because the software system will need to display prices and process users’ orders in real time.