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Database Systems: Design, Implementation, and Management
Share this book on Facebook. Share this book on Twitter. New "Book in great condition. Seller: lsylvester 0. Seller: Dougall90 0. Throughout this book, a very detailed set of software development rules will be presented. This class focuses on real-time embedded systems written in C, but most of the design processes should apply to other languages as well.
At first, it may seem radical to force such a rigid structure to software. We might wonder if creativity will be sacrificed in the process. True creativity is more about good solutions to important problems and not about being sloppy and inconsistent. Because software maintenance is a critical task, the time spent organizing, documenting, and testing during the initial development stages will reap huge dividends throughout the life of the software project.
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Observation: The easiest way to debug is to write software without any bugs. We define clients as programmers who will use our software. A client develops software that will call our functions. We define coworkers as programmers who will debug and upgrade our software. A coworker, possibly ourselves, develops, tests, and modifies our software. Writing quality software has a lot to do with attitude.
We should be embarrassed to ask our coworkers to make changes to our poorly written software. Since so much software development effort involves maintenance, we should create software modules that are easy to change. In other words, we should expect each piece of our code will be read by another engineer in the future, whose job it will be to make changes to our code.
We might be tempted to quit a software project once the system is running, but this short time we might save by not organizing, documenting, and testing will be lost many times over in the future when it is time to update the code. As project managers, we must reward good behavior and punish bad behavior.
A company, in an effort to improve the quality of their software products, implemented the following policies. The employees in the customer relations department receive a bonus for every software bug that they can identify. These bugs are reported to the software developers, who in turn receive a bonus for every bug they fix.
We should demand of ourselves that we deliver bug-free software to our clients. Again, we should be embarrassed when our clients report bugs in our code. We should be mortified when other programmers find bugs in our code. There are a few steps we can take to facilitate this important aspect of software design. Test it now. When we find a bug, fix it immediately. The longer we put off fixing a mistake the more complicated the system becomes, making it harder to find.
Remember that bugs do not go away on their own, but we can make the system so complex that the bugs will manifest themselves in mysterious and obscure ways. For the same reason, we should completely test each module individually, before combining them into a larger system. We should not add new features before we are convinced the existing system is bug-free. In this way, we start with a working system, add features, and then debug this system until it is working again.
This incremental approach makes it easier to track progress.
It allows us to undo bad decisions, because we can always revert back to a previously working system. Adding new features before the old ones are debugged is very risky. In addition, once a bug is introduced, the longer we wait to remove it, the harder it will be to correct. This is particularly true when the bugs interact with each other. Conversely, with the incremental approach, when the project schedule slips, we can deliver a working system at the deadline that supports some of the features.
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Plan for testing. How to test each module should be considered at the start of a project. In particular, testing should be included as part of the design of both hardware and software components.
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Our testing and the client's usage go hand in hand. In particular, how we test the module will help the client understand the context and limitations of how our component is to be used. Get help.
ISBN 10: 1111969604
Use whatever features are available for organization and debugging. Pay attention to warnings, because they often point to misunderstandings about data or functions.
Misunderstanding of assumptions that can cause bugs when the software is upgraded, or reused in a different context than originally conceived. Remember that computer time is a lot cheaper than programmer time. Deal with the complexity. These early systems, due to their small size, were inherently simple.
The explosion of hardware technology both in speed and size has led to a similar increase in the size of software systems. Some people forecast that by the next decade, automobiles will have 10 million lines of code in their embedded systems. The only hope for success in a large software system will be to break it into simple modules. In most cases, the complexity of the problem itself cannot be avoided.hukusyuu-mobile.com/wp-content/camera/1533-phone-message-locate.php
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Nevertheless, a complex system can be created out of simple components. A real creative effort is required to orchestrate simple building blocks into larger modules, which themselves are grouped to create even larger systems. Use your creativity to break a complex problem into simple components, rather than developing complex solutions to simple problems. Observation: There are two ways of constructing a software design: one way is to make it so simple that there are obviously no deficiencies and the other way is make it so complicated that there are no obvious deficiencies.
A program module that performs a well-defined task can be packaged up and defined as a single entity. Functions in that module can be invoked whenever a task needs to be performed. In these languages, functions return a parameter and procedures do not. Most high-level languages however define program modules as functions, whether they return a parameter or not. A subroutine is the assembly language version of a function. Consequently, subroutines may or may not have input or output parameters.
Formally, there are two components to a subroutine: definition and invocation. The subroutine definition specifies the task to be performed. In other words, it defines what will happen when executed. The syntax for an assembly subroutine begins with a label, which will be the name of the subroutine and ends with a return instruction.
The definition of a subroutine includes a formal specification its input parameters and output parameters. In well-written software, the task performed by a subroutine will be well-defined and logically complete. The subroutine invocation is inserted to the software system at places when and where the task should be performed. There are three parts to a subroutine invocation: pass input parameters, subroutine call, and accept output parameters. If there are input parameters, the calling program must establish the values for input parameters before it calls the subroutine.
A BL instruction is used to call the subroutine.
After the subroutine finishes, and if there are output parameters, the calling program accepts the return value s. In this chapter, we will pass parameters using the registers. If the register contains a value, the parameter is classified as call by value. If the register contains an address, which points to the value, then the parameter is classified as call by reference. For example, consider a subroutine that samples the bit ADC, as drawn in Figure 7.
An analog input signal is connected to ADC0. The details of how the ADC works will be presented later in the class, but for now we focus on the defining and invoking subroutines. The execution sequence begins with the calling program setting up the input parameters. The subroutine performs a well-defined task.
In this case, it takes the channel number in Register R0 and performs an analog to digital conversion, placing the digital representation of the analog input into Register R0. It is the responsibility of the calling program to accept the return parameter. In this case, it simply stores the result into variable n.
In this example, both the input and output parameters are call by value. The overall goal of modular programming is to enhance clarity. The smaller the task, the easier it will be to understand. In order to make modules more independent we strive to minimize coupling.
A quantitative measure of coupling is the number of bytes per second bandwidth that are transferred from one module to another. On the other hand, information stored in public global variables can be quite difficult to track.