C Introduction

[Jeremias Resendez]

Teachersoften tell students that an introduction should be only as long as it needs to be to do its job, which you might find frustrating and vague. A good introduction begins with a sentence that will interest the reader and entice them to read the rest of the essay, often called a hook. The hook can be an unexpected question, a shocking sentence, an interesting statistic, a powerful quote, or many other possibilities.

The introduction can be the hardest part of an essay to write because you have to know what you will say in the essay. When a writer is struggling with their introduction, they sometimes find that writing it after they write the body of the essay is easier.

Note that what constitutes a good introduction may vary widely based on the kind of paper you are writing and the academic discipline in which you are writing it. If you are uncertain what kind of introduction is expected, ask your instructor.

You never get a second chance to make a first impression. The opening paragraph of your paper will provide your readers with their initial impressions of your argument, your writing style, and the overall quality of your work. A vague, disorganized, error-filled, off-the-wall, or boring introduction will probably create a negative impression. On the other hand, a concise, engaging, and well-written introduction will start your readers off thinking highly of you, your analytical skills, your writing, and your paper.

Your introduction is an important road map for the rest of your paper. Your introduction conveys a lot of information to your readers. You can let them know what your topic is, why it is important, and how you plan to proceed with your discussion. In many academic disciplines, your introduction should contain a thesis that will assert your main argument. Your introduction should also give the reader a sense of the kinds of information you will use to make that argument and the general organization of the paragraphs and pages that will follow. After reading your introduction, your readers should not have any major surprises in store when they read the main body of your paper.

Start by thinking about the question (or questions) you are trying to answer. Your entire essay will be a response to this question, and your introduction is the first step toward that end. Your direct answer to the assigned question will be your thesis, and your thesis will likely be included in your introduction, so it is a good idea to use the question as a jumping off point. Imagine that you are assigned the following question:

Pay special attention to your first sentence. Start off on the right foot with your readers by making sure that the first sentence actually says something useful and that it does so in an interesting and polished way.

Ask a friend to read your introduction and then tell you what they expect the paper will discuss, what kinds of evidence the paper will use, and what the tone of the paper will be. If your friend is able to predict the rest of your paper accurately, you probably have a good introduction.

This is CS50x , Harvard University's introduction to the intellectual enterprises of computer science and the art of programming for majors and non-majors alike, with or without prior programming experience. An entry-level course taught by David J. Malan, CS50x teaches students how to think algorithmically and solve problems efficiently. Topics include abstraction, algorithms, data structures, encapsulation, resource management, security, software engineering, and web development. Languages include C, Python, SQL, and JavaScript plus CSS and HTML. Problem sets inspired by real-world domains of biology, cryptography, finance, forensics, and gaming. The on-campus version of CS50x , CS50, is Harvard's largest course.

Direct costs are neither subtle nor ambiguous. Running a service with a team that relies on manual intervention for both change management and event handling becomes expensive as the service and/or traffic to the service grows, because the size of the team necessarily scales with the load generated by the system.

The indirect costs of the development/ops split can be subtle, but are often more expensive to the organization than the direct costs. These costs arise from the fact that the two teams are quite different in background, skill set, and incentives. They use different vocabulary to describe situations; they carry different assumptions about both risk and possibilities for technical solutions; they have different assumptions about the target level of product stability. The split between the groups can easily become one of not just incentives, but also communication, goals, and eventually, trust and respect. This outcome is a pathology.

Common to all SREs is the belief in and aptitude for developing software systems to solve complex problems. Within SRE, we track the career progress of both groups closely, and have to date found no practical difference in performance between engineers from the two tracks. In fact, the somewhat diverse background of the SRE team frequently results in clever, high-quality systems that are clearly the product of the synthesis of several skill sets.

The result of our approach to hiring for SRE is that we end up with a team of people who (a) will quickly become bored by performing tasks by hand, and (b) have the skill set necessary to write software to replace their previously manual work, even when the solution is complicated. SREs also end up sharing academic and intellectual background with the rest of the development organization. Therefore, SRE is fundamentally doing work that has historically been done by an operations team, but using engineers with software expertise, and banking on the fact that these engineers are inherently both predisposed to, and have the ability to, design and implement automation with software to replace human labor.

By design, it is crucial that SRE teams are focused on engineering. Without constant engineering, operations load increases and teams will need more people just to keep pace with the workload. Eventually, a traditional ops-focused group scales linearly with service size: if the products supported by the service succeed, the operational load will grow with traffic. That means hiring more people to do the same tasks over and over again.

Despite these net gains, the SRE model is characterized by its own distinct set of challenges. One continual challenge Google faces is hiring SREs: not only does SRE compete for the same candidates as the product development hiring pipeline, but the fact that we set the hiring bar so high in terms of both coding and system engineering skills means that our hiring pool is necessarily small. As our discipline is relatively new and unique, not much industry information exists on how to build and manage an SRE team (although hopefully this book will make strides in that direction!). And once an SRE team is in place, their potentially unorthodox approaches to service management require strong management support. For example, the decision to stop releases for the remainder of the quarter once an error budget is depleted might not be embraced by a product development team unless mandated by their management.

Postmortems should be written for all significant incidents, regardless of whether or not they paged; postmortems that did not trigger a page are even more valuable, as they likely point to clear monitoring gaps. This investigation should establish what happened in detail, find all root causes of the event, and assign actions to correct the problem or improve how it is addressed next time. Google operates under a blame-free postmortem culture, with the goal of exposing faults and applying engineering to fix these faults, rather than avoiding or minimizing them.

Product development and SRE teams can enjoy a productive working relationship by eliminating the structural conflict in their respective goals. The structural conflict is between pace of innovation and product stability, and as described earlier, this conflict often is expressed indirectly. In SRE we bring this conflict to the fore, and then resolve it with the introduction of an error budget.

So how do we want to spend the error budget? The development team wants to launch features and attract new users. Ideally, we would spend all of our error budget taking risks with things we launch in order to launch them quickly. This basic premise describes the whole model of error budgets. As soon as SRE activities are conceptualized in this framework, freeing up the error budget through tactics such as phased rollouts and 1% experiments can optimize for quicker launches.

Humans add latency. Even if a given system experiences more actual failures, a system that can avoid emergencies that require human intervention will have higher availability than a system that requires hands-on intervention. When humans are necessary, we have found that thinking through and recording the best practices ahead of time in a "playbook" produces roughly a 3x improvement in MTTR as compared to the strategy of "winging it." The hero jack-of-all-trades on-call engineer does work, but the practiced on-call engineer armed with a playbook works much better. While no playbook, no matter how comprehensive it may be, is a substitute for smart engineers able to think on the fly, clear and thorough troubleshooting steps and tips are valuable when responding to a high-stakes or time-sensitive page. Thus, Google SRE relies on on-call playbooks, in addition to exercises such as the "Wheel of Misfortune,"7 to prepare engineers to react to on-call events.

This trio of practices effectively minimizes the aggregate number of users and operations exposed to bad changes. By removing humans from the loop, these practices avoid the normal problems of fatigue, familiarity/contempt, and inattention to highly repetitive tasks. As a result, both release velocity and safety increase.

The following is an introduction to the Medical Subject Headings (MeSH) thesaurus, including its use and structure, as well as recent updates and availability of data. For simplest access to MeSH we suggest the MeSH Browser, an interactive Web application for searching and browsing MeSH data.

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