Systems Analysis and Design: Core Concepts




Systems Analysis and Design:Core Concepts

The major goal of systems analysis and design is to improve organizational      systems. Often this process involves developing or acquiring application software and training employees to use it. Application software, also called a system,is designed to support a specific organizational function or process, such as inventory management, payroll, or market analysis. The goal of application software is to turn data into information. For example, software developed for the inventory department at a bookstore may keep track of the number of books in stock of the latest best seller. Software for the payroll department may keep track of the changing pay rates of employees. A variety of off-the-shelf application software can be purchased, including WordPerfect, Excel, and PowerPoint. However, off-the-shelf software may not fit the needs of a particular organization, and so the organization must develop its own product.

   In addition to application software, the information system includes:

The hardware and systems software on which the application software runs.     Note that the systems software helps the computer function, whereas the         application software helps the user perform tasks such as writing a paper,       preparing a spreadsheet, and linking to the Internet.

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 Documentation and training materials, which are materials created by the       systems analyst to help employees use the software they’ve helped create. 

 The specific job roles associated with the overall system, such as the people     who run the computers and keep the software operating.

 Controls, which are parts of the software written to help prevent fraud and       theft. 

 The people who use the software in order to do their jobs.

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          The components of a computer-based information system application are summarized in Figure 1-2. We address all the dimensions of the overall system,

Systems Analysis and Design: Core Concepts

  with particular emphasis on application software development—your primary    responsibility as a systems analyst.

  Our goal is to help you understand and follow the software engineering              process that leads to the creation of information systems. As shown in Figure    1-3, proven methodologies, techniques, and tools are central to software          engineering processes.

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  Methodologies are a sequence of step-by-step approaches that help develop    your final product: the information system. Most methodologies incorporate        several development techniques, such as direct observations and interviews    with users of the current system.

  Techniques are processes that you, as an analyst, will follow to help ensure      that your work is well thought-out, complete, and comprehensible to others        on your project team. Techniques provide support for a wide range of tasks,      including conducting thorough interviews with current and future users of the    information system to determine what your system should do, planning and      managing the activities in a systems development project, diagramming how    the system will function, and designing the reports, such as invoices, your          system will generate for its users to perform their jobs.

  Tools are computer programs, such as computer-aided software engineering    (CASE) tools, that make it easy to use specific techniques. These three            elements— methodologies, techniques, and tools—work together to form an    organizational approach to systems analysis and design.

Systems Analysis and Design: Core Concepts          

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            FIGURE 1-3 The software engineering process uses proven                                              methodologies, techniques, and tools.     

 

  In the rest of this chapter, you will learn about approaches to systems                development—the data- and process-oriented approaches. You will also            identify the various people who develop systems and the different types of        systems they develop. The chapter ends with a discussion of some of the          methodologies, techniques, and tools created to support the systems                development process. Before we talk more about computer-based                      information systems, let’s briefly discuss what we mean by the word system.                                     

 

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Frequently Asked Questions

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Ans: When information is stored in a computer system, we want to keep it safe from physical damage (reliability) and improper access (protection). Reliability is generally provided by duplicate copies of files. Many computers have systems programs that automatically (or through computer-operator intervention) copy disk files to tape at regular intervals (once per day or week or month) to maintain a copy should a file system be accidentally destroyed. view more..
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Ans: In the previous sections, we explored the motivation for file sharing and some of the difficulties involved in allowing users to share files. Such file sharing is very desirable for users who want to collaborate and to reduce the effort required to achieve a computing goal. Therefore, user-oriented operating systems must accommodate the need to share files in spite of the inherent difficulties. In this section, we examine more aspects of file sharing view more..
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Ans: Modern disk drives are addressed as large one-dimensional arrays of logical blocks, where the logical block is the smallest unit of transfer. The size of a logical block is usually 512 bytes, although some disks can be low-level formatted to have a different logical block size, such as 1,024 bytes. view more..
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Ans: Goal of systems analysis and design is to improve organizational systems. This process involves developing or acquiring application software and training employees. view more..
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Ans: Disk Scheduling One of the responsibilities of the operating system is to use the hardware efficiently. For the disk drives, meeting this responsibility entails having fast access time and large disk bandwidth. The access time has two major components. The seek time is the time for the disk arm to move the heads to the cylinder containing the desired sector. The rotational latency is the additional time for the disk to rotate the desired sector to the disk head. The disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer. We can improve both the access time and the bandwidth by scheduling the servicing of disk I/O requests in a good order. Whenever a process needs I/O to or from the disk, it issues a system call to the operating system view more..
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Ans: The operating system is responsible for several other aspects of disk management, too. Here we discuss disk initialization, booting from disk, and bad-block recovery. view more..
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Ans: File-System Structure Disks provide the bulk of secondary storage on which a file system is maintained. They have two characteristics that make them a convenient medium for storing multiple files: 1. A disk can be rewritten in place; it is possible to read a block from the disk, modify the block, and write it back into the same place. 2. A disk can access directly any given block of information it contains. Thus, it is simple to access any file either sequentially or randomly, and switching from one file to another requires only moving the read-write heads and waiting for the disk to rotate. view more..
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Ans: An operating system provides an environment for the execution of programs. It provides certain services to programs and to the users of those programs. The specific services provided, of course, differ from one operating system to another, but we can identify common classes. These operating-system services are provided for the convenience of the programmer, to make the programming task easier. services are : User interface, Program execution, I/O operations, File-system manipulation, Communications, Error detection, Resource allocation, Accounting, Protection and security view more..
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Ans: User Operating-System Interface There are two fundamental approaches for users to interface with the operating system. One technique is to provide a command-line interface or command interpreter that allows users to directly enter commands that are to be performed by the operating system. The second approach allows the user to interface with the operating system via a graphical user interface or GUI. view more..
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Ans: Operating-System Design and Implementation In this section, we discuss problems we face in designing and implementing an operating system. There are, of course, no complete solutions to such problems, but there are approaches that have proved successful. view more..
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Ans: Virtual Machines The layered approach described in Section 2.7.2 is taken to its logical conclusion in the concept of a virtual machine. The fundamental idea behind a virtual machine is to abstract the hardware of a single computer (the CPU, memory, disk drives, network interface cards, and so forth) into several different execution environments, thereby creating the illusion that each separate execution environment is running its own private computer. By using CPU scheduling (Chapter 5) and virtual-memory techniques (Chapter 9), an operating system can create the illusion that a process has its own processor with its own (virtual) memory. Normally, a process has additional features, such as system calls and a file system, that are not provided by the bare hardware. view more..
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Ans: Deadlock Prevention As we noted in Section 7.2.1, for a deadlock to occur, each of the four necessary conditions must hold. By ensuring that at least one of these conditions cannot hold, we can prevent the occurrence of a deadlock. We elaborate on this approach by examining each of the four necessary conditions separately. view more..
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Ans: Deadlock Avoidance Deadlock-prevention algorithms, as discussed in Section 7.4, prevent deadlocks by restraining how requests can be made. The restraints ensure that at least one of the necessary conditions for deadlock cannot occur and, hence, that deadlocks cannot hold. Possible side effects of preventing deadlocks by this method, however, are low device utilization and reduced system throughput. An alternative method for avoiding deadlocks is to require additional information about how resources are to be requested. For example, in a system with one tape drive and one printer, the system might need to know that process P will request first the tape drive and then the printer before releasing both resources, whereas process Q will request first the printer and then the tape drive. With this knowledge of the complete sequence of requests and releases for each process, the system can decide for each request whether or not the process should wait in order to avoid a possible future deadlock. view more..
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Ans: Recovery From Deadlock When a detection algorithm determines that a deadlock exists, several alternatives are available. One possibility is to inform the operator that a deadlock has occurred and to let the operator deal with the deadlock manually. Another possibility is to let the system recover from the deadlock automatically. There are two options for breaking a deadlock. One is simply to abort one or more processes to break the circular wait. The other is to preempt some resources from one or more of the deadlocked processes. view more..
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Ans: Stable-Storage Implementation We introduced the write-ahead log, which requires the availability of stable storage. By definition, information residing in stable storage is never lost. To implement such storage, we need to replicate the needed information on multiple storage devices (usually disks) with independent failure modes. We need to coordinate the writing of updates in a way that guarantees that a failure during an update will not leave all the copies in a damaged state and that, when we are recovering from a failure, we can force all copies to a consistent and correct value, even if another failure occurs during the recovery. In this section, we discuss how to meet these needs. view more..
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Ans: File-System Mounting Just as a file must be opened before it is used, a file system must be mounted before it can be available to processes on the system. More specifically, the directory structure can be built out of multiple volumes, which must be mounted to make them available within the file-system name space. The mount procedure is straightforward. The operating system is given the name of the device and the mount point—the location within the file structure where the file system is to be attached. Typically, a mount point is an empty directory. view more..
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Ans: Access Methods Files store information. When it is used, this information must be accessed and read into computer memory. The information in the file can be accessed in several ways. Some systems provide only one access method for files. Other systems, such as those of IBM, support many access methods, and choosing the right one for a particular application is a major design problem. view more..
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Ans: Directory implementation The selection of directory-allocation and directory-management algorithms significantly affects the efficiency, performance, and reliability of the file system. In this section, we discuss the trade-offs involved in choosing one of these algorithms. view more..




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