In waterfall development, milestones are clear markers or deadlines that delineate space between when one task ends and another begins, typically in the form of handoff and kickoff meetings. Consider the car analogy from earlier: If the agile approach is to continue to add cupholders and tweak the dashboard display as the car rolls off the assembly line, a milestone, in contrast, involves bringing work to a stop, celebrating that the vehicle has left the factory, and figuring out what comes next

Like the name suggests, agile also emphasizes speed. The sprint cycle allows teams to react to feedback from users swiftly and adjust the product accordingly. It accounts for the ever-changing nature of our work and includes built-in meetings or cer

Books on agile software development tend to make use of an automotive analogy. If you want to build a car, they declare, start by building a skateboard. Sell that skateboard to customers, then build a scooter. Next, you’ll build a bike, then a motorcycle, and finally a car.

Ideally, M1 and M2 should be independent even from the standpoint of databases, as shown in the next figure. The reason is that when you have a single database, it too can become a bottleneck to the system’s evolution.

Complexity: When two modules run in the same process, communication between them occurs through method calls. But when they are on different machines, the communication must use some communication protocol, such as HTTP. For this reason, developers who work with microservices need to master and use a set of technologies for communication over networks.

View: Classes responsible for implementing the system’s graphical interface, including windows, buttons, menus, scroll bars, etc.

User Interface: Also known as the presentation layer, it is responsible for all user interaction, handling the display of data, and processing inputs and interface events such as button clicks and text highlighting. Usually, this layer is implemented as a desktop application. For example, an academic system should provide a graphical interface for instructors to enter grades for their classes. The main element of this interface can be a form with two columns: student name and grade. The code implementing this form resides in the interface layer.

Business Logic: Also known as the application layer, it implements the system’s business rules. In the academic system example, a business rule could require that grades must be greater than or equal to zero and less than or equal to the value of the exam. When an instructor enters the grades for a exam, it’s up to the logic layer to check whether this rule is followed. Another business rule could state that after the grades are entered, the students should be notified via email.

Database: This layer stores the data manipulated by the system. For example, in our academic system, after the grades are entered and validated, they are saved in a database.