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H e had the classic look of a senior executive for a major software company—mid-40s, slightly graying at the temples, trim and athletic, with eyes that penetrated the listener as he spoke. But what he said shocked me. “Software is dead.” I blinked with surprise and then smiled. “You’re joking, right? The world is driv... | “You’re joking, right? |
I had to agree. “So, your life will be much simpler. You guys won’t have to worry about five different versions of the same App in use across tens of thousands of users.” He smiled. “Absolutely. Only the most current version residing on our servers. When we make a change or a correction, we supply updated functionality... | Is software really dead? |
programmer are the same questions that are asked when modern computer-based systems are built:1 4 CHAPTER 1 SOFTWARE AND SOFTWARE ENGINEERING 1 In an excellent book of essays on the software business, Tom DeMarco [DeM95] argues the coun- terpoint. He states: “Instead of asking why software costs so much, we need to beg... | Why does it take so long to get software finished? |
Netsourcing—the World Wide Web is rapidly becoming a computing engine as well as a content provider. The challenge for software engineers is to architect simple (e.g., personal financial planning) and sophisticated applica- tions that provide a benefit to targeted end-user markets worldwide. Open source—a growing trend... | What do I do if I encounter a legacy system that exhibits poor quality? ? |
that were never archived, a poorly managed change history—the list can be quite long. And yet, these systems support “core business functions and are indispensable to the business.” What to do? The only reasonable answer may be: Do nothing, at least until the legacy system must undergo some significant change. If the l... | What to do? |
internal communications and external relations, and between art and technology.” The following attributes are encountered in the vast majority of WebApps. Network intensiveness. A WebApp resides on a network and must serve the needs of a diverse community of clients. The network may enable world- wide access and commun... | What characteristic differentiates WebApps from other software? ? |
increase, demands for adaptation and enhancement will also grow. It follows that software should be maintainable. These simple realities lead to one conclusion: software in all of its forms and across all of its application domains should be engineered. And that leads us to the topic of this book—software engineering. ... | What are the “sound engineering principles” that can be applied to computer software development? |
that must be established for effective delivery of software engineering technology. The software process forms the basis for management control of software projects and establishes the context in which technical methods are applied, work products (models, documents, data, reports, forms, etc.) are produced, milestones ... | What are the elements of a software process? ? |
A process framework establishes the foundation for a complete software engi- neering process by identifying a small number of framework activities that are appli- cable to all software projects, regardless of their size or complexity. In addition, the process framework encompasses a set of umbrella activities that are ... | What are the five generic process framework activities? ? |
For many software projects, framework activities are applied iteratively as a project progresses. That is, communication, planning, modeling, construction, and deployment are applied repeatedly through a number of project iterations. Each project iteration produces a software increment that provides stakeholders with a... | How do process models differ from one another? ? |
• Manner in which quality assurance activities are applied • Manner in which project tracking and control activities are applied • Overall degree of detail and rigor with which the process is described • Degree to which the customer and other stakeholders are involved with the project • Level of autonomy given to the s... | But how does the practice of software engineering fit in? |
3. Carry out the plan (code generation). 4. Examine the result for accuracy (testing and quality assurance). In the context of software engineering, these commonsense steps lead to a series of essential questions [adapted from Pol45]: Understand the problem. It’s sometimes difficult to admit, but most of us suffer from... | It’s worth spending a little time answering a few simple questions: • Who has a stake in the solution to the problem? |
Examine the result. You can’t be sure that your solution is perfect, but you can be sure that you’ve designed a sufficient number of tests to uncover as many errors as possible. • Is it possible to test each component part of the solution? Has a reasonable testing strategy been implemented? • Does the solution produce ... | Is it possible to test each component part of the solution? |
Management myths. Managers with software responsibility, like managers in most disciplines, are often under pressure to maintain budgets, keep schedules from slipping, and improve quality. Like a drowning person who grasps at a straw, a soft- ware manager often grasps at belief in a software myth, if that belief will l... | Won’t that provide my people with everything they need to know? |
Many software professionals recognize the fallacy of the myths just described. Regrettably, habitual attitudes and methods foster poor management and technical practices, even when reality dictates a better approach. Recognition of software realities is the first step toward formulation of practical solutions for softw... | The conversation: Joe: Okay, Lee, what’s this I hear about your folks developing a what? |
1.5. Consider the seven software categories presented in Section 1.1.2. Do you think that the same approach to software engineering can be applied for each? Explain your answer. 1.6. Figure 1.3 places the three software engineering layers on top of a layer entitled “a quality focus.” This implies an organizational qual... | Do you think that the same approach to software engineering can be applied for each? |
THE SOFTWARE PROCESS 29 P A R T One I n this part of Software Engineering: A Practitioner’s Approach you’ll learn about the process that provides a framework for software engineering practice. These questions are addressed in the chapters that follow: • What is a software process? • What are the generic framework acti... | These questions are addressed in the chapters that follow: • What is a software process? |
I n a fascinating book that provides an economist’s view of software and soft- ware engineering, Howard Baetjer, Jr. [Bae98], comments on the software process: Because software, like all capital, is embodied knowledge, and because that knowl- edge is initially dispersed, tacit, latent, and incomplete in large measure,... | What is it? |
CHAPTER 2 PROCESS MODELS 31 But what exactly is a software process from a technical point of view? Within the context of this book, I define a software process as a framework for the activities, ac- tions, and tasks that are required to build high-quality software. Is “process” syn- onymous with software engineering? T... | But what exactly is a software process from a technical point of view? |
2.1.1 Defining a Framework Activity Although I have described five framework activities and provided a basic defini- tion of each in Chapter 1, a software team would need significantly more infor- mation before it could properly execute any one of these activities as part of the software process. Therefore, you are fac... | Therefore, you are faced with a key question: What actions are appropriate for a framework activity, given the nature of the problem to be solved, the characteristics of the people doing the work, and the stakeholders who are sponsor- ing the project? |
CHAPTER 2 PROCESS MODELS 33 (d) Parallel process flow (c) Evolutionary process flow Communication Planning Modeling (a) Linear process flow Construction Deployment Communication Planning Modeling Construction Deployment Construction Deployment Communication Planning Modeling Time (b) Iterative process flow Planning Mod... | How does a framework activity change as the nature of the project changes? ? |
2.1.3 Process Patterns Every software team encounters problems as it moves through the software process. It would be useful if proven solutions to these problems were readily available to the team so that the problems could be addressed and resolved quickly. A process pattern1 describes a process-related problem that i... | What is a process pattern? ? |
Initial context. Describes the conditions under which the pattern applies. Prior to the initiation of the pattern: (1) What organizational or team-related ac- tivities have already occurred? (2) What is the entry state for the process? (3) What software engineering information or project information already exists? For... | Prior to the initiation of the pattern: (1) What organizational or team-related ac- tivities have already occurred? |
2.2 PROCESS ASSESSMENT AND IMPROVEMENT The existence of a software process is no guarantee that software will be delivered on time, that it will meet the customer’s needs, or that it will exhibit the technical characteristics that will lead to long-term quality characteristics (Chapters 14 and 16). Process patterns mus... | What formal techniques are available for assessing the software process? ? |
CMM-Based Appraisal for Internal Process Improvement (CBA IPI)— provides a diagnostic technique for assessing the relative maturity of a software organization; uses the SEI CMM as the basis for the assessment [Dun01]. SPICE (ISO/IEC15504)—a standard that defines a set of requirements for software process assessment. Th... | If prescriptive process models5 strive for structure and order, are they inappropri- ate for a software world that thrives on change? |
models (and the order they imply) and replace them with something less structured, do we make it impossible to achieve coordination and coherence in software work? There are no easy answers to these questions, but there are alternatives available to software engineers. In the sections that follow, I examine the prescri... | models (and the order they imply) and replace them with something less structured, do we make it impossible to achieve coordination and coherence in software work? |
assurance actions to the actions associated with communication, modeling, and early construction activities. As a software team moves down the left side of the V, basic problem requirements are refined into progressively more detailed and techni- cal representations of the problem and its solution. Once code has been g... | Why does the waterfall model sometimes fail? ? |
formats). The quick design leads to the construction of a prototype. The prototype is deployed and evaluated by stakeholders, who provide feedback that is used to fur- ther refine requirements. Iteration occurs as the prototype is tuned to satisfy the needs of various stakeholders, while at the same time enabling you t... | But what do you do with the prototype when it has served the purpose described earlier? |
development is complete. If the concept is to be developed into an actual product, the process proceeds outward on the spiral and a “new product development proj- ect” commences. The new product will evolve through a number of iterations around the spiral. Later, a circuit around the spiral might be used to represent a... | Did you say that we regenerate the plan with each tour around the spiral, Doug? |
technology that is used to create the components, the component-based develop- ment model incorporates the following steps (implemented using an evolutionary approach): 1. Available component-based products are researched and evaluated for the application domain in question. 2. Component integration issues are consider... | If formal methods can demonstrate software correctness, why is it they are not widely used? ? |
the needs of the project team that is actually doing software engineering work. In an ideal setting, you would create a process that best fits your needs, and at the same time, meets the broader needs of the team and the organization. Alternatively, the team itself can create its own process, and at the same time meet ... | What framework activities are used during PSP? ? |
PSP stresses the need to identify errors early and, just as important, to understand the types of errors that you are likely to make. This is accomplished through a rigor- ous assessment activity performed on all work products you produce. PSP represents a disciplined, metrics-based approach to software engineering tha... | Can PSP be used as an effective software process at a personal level? |
2.8. Provide three examples of software projects that would be amenable to the prototyping model. Be specific. 2.9. What process adaptations are required if the prototype will evolve into a deliverable system or product? 2.10. Provide three examples of software projects that would be amenable to the incremental model. ... | What process adaptations are required if the prototype will evolve into a deliverable system or product? |
I n 2001, Kent Beck and 16 other noted software developers, writers, and con- sultants [Bec01a] (referred to as the “Agile Alliance”) signed the “Manifesto for Agile Software Development.” It stated: We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have com... | What is it? |
A manifesto is normally associated with an emerging political movement—one that attacks the old guard and suggests revolutionary change (hopefully for the better). In some ways, that’s exactly what agile development is all about. Although the underlying ideas that guide agile development have been with us for many year... | Does this mean that a recognition of challenges posed by modern realities causes you to discard valuable software engineering principles, concepts, methods, and tools? |
3.1 WHAT IS AGILITY? Just what is agility in the context of software engineering work? Ivar Jacobson [Jac02a] provides a useful discussion: Agility has become today’s buzzword when describing a modern software process. Every- one is agile. An agile team is a nimble team able to appropriately respond to changes. Change ... | 3.1 WHAT IS AGILITY? |
not adversely affect the outcome of the project. But what if we fast-forward a num- ber of months? The team is in the middle of validation testing (something that occurs relatively late in the project), and an important stakeholder is requesting a major functional change. The change requires a modification to the archi... | But what if we fast-forward a num- ber of months? |
2. For many types of software, design and construction are interleaved. That is, both activities should be performed in tandem so that design models are proven as they are created. It is difficult to predict how much design is necessary before construction is used to prove the design. 3. Analysis, design, construction,... | Given these three assumptions, an important question arises: How do we create a process that can manage unpredictability? |
9. Continuous attention to technical excellence and good design enhances agility. 10. Simplicity—the art of maximizing the amount of work not done—is essential. 11. The best architectures, requirements, and designs emerge from self– organizing teams. 12. At regular intervals, the team reflects on how to become more ef... | The real question is: What is the best way to achieve it? |
3.3.3 Human Factors Proponents of agile software development take great pains to emphasize the impor- tance of “people factors.” As Cockburn and Highsmith [Coc01a] state, “Agile devel- opment focuses on the talents and skills of individuals, molding the process to specific people and teams.” The key point in this state... | Barry Boehm What key traits must exist among the people on an effective software team? ? |
feel for required output and major features and functionality. Listening leads to the creation of a set of “stories” (also called user stories) that describe required output, features, and functionality for software to be built. Each story (similar to use cases described in Chapter 5) is written by the customer and is ... | What is an XP “story”? ? |
that “can radically improve the design” [Fow00]. It should be noted, however, that the effort required for refactoring can grow dramatically as the size of an application grows. A central notion in XP is that design occurs both before and after coding com- mences. Refactoring means that design occurs continuously as th... | What is pair programming? ? |
As the individual unit tests are organized into a “universal testing suite” [Wel99], integration and validation testing of the system can occur on a daily basis. This pro- vides the XP team with a continual indication of progress and also can raise warn- ing flags early if things go awry. Wells [Wel99] states: “Fixing ... | What new practices are appended to XP to create IXP? ? |
addressed as XP practice matures. Among the issues that continue to trouble some critics of XP are:10 • Requirements volatility. Because the customer is an active member of the XP team, changes to requirements are requested informally. As a consequence, the scope of the project can change and earlier work may have to b... | What are some of the issues that lead to an XP debate? ? |
3.5 OTHER AGILE PROCESS MODELS The history of software engineering is littered with dozens of obsolete process descriptions and methodologies, modeling methods and notations, tools, and technology. Each flared in notoriety and was then eclipsed by something new and (purportedly) better. With the introduction of a wide ... | Doug: Sure Jamie, what’s up? |
every 24 hours 30 days Scrum: 15 minute daily meeting. Team members respond to basics: 1) What did you do since last Scrum meeting? 2) Do you have any obstacles? 3) What will you do before next meeting? Sprint Backlog: Feature(s) assigned to sprint Product Backlog: Prioritized product features desired by the custom... | Team members respond to basics: 1) What did you do since last Scrum meeting? |
Changes (e.g., backlog work items) are not introduced during the sprint. Hence, the sprint allows team members to work in a short-term, but stable environment. Scrum meetings—are short (typically 15 minutes) meetings held daily by the Scrum team. Three key questions are asked and answered by all team members [Noy02]: •... | What did you do since the last team meeting? |
(6) reducing the time required to request and get a decision that affects the software or the process that is applied to create it, and (7) streamlining the manner in which information is transmitted to all stakeholders involved in the process. For a detailed discussion of LSD and pragmatic guidelines for implementing ... | Is there an agile approach to soft- ware engineering modeling that might provide an alternative? |
3.6 A TOOL SET FOR THE AGILE PROCESS Some proponents of the agile philosophy argue that automated software tools (e.g., design tools) should be viewed as a minor supplement to the team’s activities, and not at all pivotal to the success of the team. However, Alistair Cockburn [Coc04] sug- gests that tools can have a be... | Are any of these things really tools? |
an emphasis on rapid delivery of software that satisfies the customer. Agile process models have been designed to address each of these issues. Extreme programming (XP) is the most widely used agile process. Organized as four framework activities—planning, design, coding, and testing—XP suggests a number of innovative ... | Can you think of a situation in which one or more of the four “values” could get a software team into trouble? |
3.6. Select one agility principle noted in Section 3.3.1 and try to determine whether each of the process models presented in this chapter exhibits the principle. [Note: I have presented an overview of these process models only, so it may not be possible to determine whether a prin- ciple has been addressed by one or m... | Why do requirements change so much? |
MODELING 95 P A R T Two I n this part of Software Engineering: A Practitioner’s Approach you’ll learn about the principles, concepts, and methods that are used to create high-quality requirements and design models. These questions are addressed in the chapters that follow: • What concepts and principles guide software ... | These questions are addressed in the chapters that follow: • What concepts and principles guide software engineering practice? |
I n a book that explores the lives and thoughts of software engineers, Ellen Ullman [Ull97] depicts a slice of life as she relates the thoughts of practitioner under pressure: I have no idea what time it is. There are no windows in this office and no clock, only the blinking red LED display of a microwave, which flashe... | What is it? |
CHAPTER 4 PRINCIPLES THAT GUIDE PRACTICE 97 A dark image of software engineering practice to be sure, but upon reflection, many of the readers of this book will be able to relate to it. People who create computer software practice the art or craft or discipline1 that is software engineering. But what is software engine... | But what is software engineering “practice”? |
Principle 2. Prepare before you communicate. Spend the time to under- stand the problem before you meet with others. If necessary, do some re- search to understand business domain jargon. If you have responsibility for conducting a meeting, prepare an agenda in advance of the meeting. Principle 3. Someone should facili... | Mark Twain What happens if I can’t come to an agreement with the customer on some project- related issue? ? |
Try as we might, it’s impossible to predict exactly how a software project will evolve. There is no easy way to determine what unforeseen technical problems will be encountered, what important information will remain undiscovered until late in the project, what misunderstandings will occur, or what business issues will... | What to do? |
Principle 6. Be realistic. People don’t work 100 percent of every day. Noise always enters into any human communication. Omissions and ambiguity are facts of life. Change will occur. Even the best software engineers make mistakes. These and other realities should be considered as a project plan is established. Principl... | For example, can the customer request a change at any time? |
get sloppy. For example, since requirements will change, there is a tendency to give requirements models short shrift. Why? Because you know that they’ll change anyway. The problem with this attitude is that without a reasonably complete requirements model, you’ll create a design (design model) that will invariably mis... | Why? |
a keyboard command might be typed, a joystick (or mouse) might be pointed in a specific direction, or a motion-sensitive device might be waved in the air. By applying these principles, a software engineer approaches a problem system- atically. But how are these principles applied in practice? This question will be an- ... | But how are these principles applied in practice? |
• Write code that is self-documenting. • Create a visual layout (e.g., indentation and blank lines) that aids understanding. Validation Principles: After you’ve completed your first coding pass, be sure you • Conduct a code walkthrough when appropriate. • Perform unit tests and correct errors you’ve uncovered. • Refac... | What are the objectives of software testing? ? |
should occur before code is written, while it is being created, and after it has been completed. Although there are many testing principles, only one is dominant: test- ing is a process of executing a program with the intent of finding an error. Deployment occurs as each software increment is presented to the customer ... | Since a focus on quality demands resources and time, is it possible to be agile and still maintain a quality focus? |
U nderstanding the requirements of a problem is among the most difficult tasks that face a software engineer. When you first think about it, devel- oping a clear understanding of requirements doesn’t seem that hard. After all, doesn’t the customer know what is required? Shouldn’t the end users have a good understanding... | After all, doesn’t the customer know what is required? |
It’s reasonable to argue that the techniques I’ll discuss in this chapter are not a true “solution” to the challenges just noted. But they do provide a solid approach for addressing these challenges. 5.1 REQUIREMENTS ENGINEERING Designing and building computer software is challenging, creative, and just plain fun. In f... | But where does the bridge originate? |
high above the project, allowing you to examine the context of the software work to be performed; the specific needs that design and construction must address; the pri- orities that guide the order in which work is to be completed; and the information, functions, and behaviors that will have a profound impact on the re... | How does a software project get started? |
stated unambiguously; that inconsistencies, omissions, and errors have been detected and corrected; and that the work products conform to the standards estab- lished for the process, the project, and the product. The primary requirements validation mechanism is the technical review (Chap- ter 15). The review team that ... | Are requirements stated clearly? |
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