Presentation on theme: "Introduction to Software Construction Chapter 1-3."— Presentation transcript:
Introduction to Software Construction Chapter 1-3
What Is Software Construction?
What we will cover?
Why Is Software Construction Important? Is a large part of software development Is the central activity in software development With a focus on construction, the individual programmer's productivity can improve enormously Construction's product, the source code, is often the only accurate description of the software Construction is the only activity that's guaranteed to be done
The power of metaphors The chemist Kekulé had a dream in which he saw a snake grasp its tail in its mouth. When he awoke, he realized that a molecular structure based on a similar ring shape would account for the properties of benzene. Further experimentation confirmed the hypothesis
Software Metaphors Metaphors have the virtue of an expected behaviour that is understood by all. unnecessary communication and misunderstanding are minimized, allows for quicker learning and a higher level of abstraction for the problem at hand. A software metaphor is more like a searchlight than a road map. it doesn't tell you where to find the answer; it tells you how to look for it. A metaphor serves more as a heuristic than it does as an algorithm. a heuristic process. This will tell you how to look for a solution, not where to find an algorithm process. Gives you specific directions for a solution, and where to look to find the solution.
Heuristic vs. algorithm The main difference the level of indirection from the solution example: Getting to someone's house Heuristic Find the last letter we mailed you. Drive to the town in the return address. When you get to town, ask someone where our house is. Everyone knows ussomeone will be glad to help you. If you can't find anyone, call us from a public phone, and we'll come get you. Algorithm Gives you the instructions directly – GPS
Common Software Metaphors (1) Software Penmanship: Writing Code looks at writing software the same way that most people think that an author writes a book. You just sit down and start writing from start all the way through to the finish. along with starting from scratch, just as in writing a story, expect to take at least one version of your program and completely through it away. this works great if you are working for yourself, however, most employers like to see productive work, not work you throw away. implies a software-development process that's too simple and rigid to be healthy
Common Software Metaphors (2) Software Farming: Growing a System like planting seeds and growing crops You design a piece, code a piece, test a piece, and add it to the system a little bit at a time. By taking small steps, you minimize the trouble you can get into at any one time a good technique is described with a bad metaphor its suggestion that you don't have any direct control over how the software develops.
Common Software Metaphors (3) Software Oyster Farming: System Accretion like a oyster gradually adding coats of calcium carbonate to a pebble to reduce the irritation. make the simplest possible version of the system that will run it doesn't have to perform realistic manipulations on data, it doesn't have to produce realistic output however, once the version is complete, we slowly add small working components to the system and test them. will eventually lead to a fully functioning system by slowly over time adding little bits of working code to make the operation smooth and pretty.
Common Software Metaphors (4) Software Construction: Building Software The image of "building" software is more useful than that of "writing" or "growing" software. It's compatible with the idea of software accretion and provides more detailed guidance. Building software implies various stages of planning, preparation, and execution that vary in kind and degree depending on what's being built.
Building houses vs. building software In building a house, you won't try to build things you can buy already built. You'll buy a washer and dryer, dishwasher, refrigerator, and freezer. Unless you're a mechanical wizard, you won't consider building them yourself. You'll also buy prefabricated cabinets, counters, windows, doors, and bathroom fixtures. If you're building a software system, you'll do the same thing. You'll make extensive use of high-level language features rather than writing your own operating-system-level code. You might also use prebuilt libraries of container classes, scientific functions, user interface classes, and database-manipulation classes. It generally doesn't make sense to code things you can buy ready- made.
The Intellectual Toolbox A good craftsman knows the right tool for the job and knows how to use it correctly. A good programmer The software practices and techniques that work become the toolbox. add what worked as well as what didn't work to the toolbox to make it more effective
Prerequisites to Construction Before beginning construction of a house, a builder reviews blueprints, checks that all permits have been obtained, and surveys the house's foundation. A builder prepares for building a skyscraper one way, a housing development a different way, and a dog-house a third way. No matter what the project, the preparation is tailored to the project's specific needs and done conscientiously before construction begins. As with building construction, much of the success or failure of the project has already been determined before construction begins. If the foundation hasn't been laid well or the planning is inadequate, the best you can do during construction is to keep damage to a minimum. The importance of these steps cannot be overstated. if this process is poorly done, we will still be lucky if the result is even working, let alone useful
Emphasizing Quality At the end of the project emphasis is on testing In the middle of the project emphasis is on good construction practices At the beginning plan for a high quality product Your design limits the end results. by the time you start construction, it is too late to correct a weak or faulty design. The best we can do in construction is to recognize that the design is bad and go back and try again. However, this can be an very expensive proposition, but at times necessary to actually save money.
Cost to fix defects (1)
Cost to fix defects (2)
Problem-Definition Prerequisite The problem definition lays the foundation for the rest of the programming process you need a clear statement of the problem before you can even think of a solution the problem definition must also be general enough that it does not presuppose a solution the definition should be in the user's language and from the user's point of view the solution may turn out to be something that is not related to computers at all
The penalty for failing to define the problem
Requirements Prerequisite Ensure : The user's needs are driving the system, not the programmers System scope is agreed upon Minimal changes will be needed after construction begins since requirements are never stable: use the checklist on pages of your text. make sure that the cost of changes is understood establish a good "change control" procedure use an approach that accommodates changes lastly you can always kill the project.
Without good requirements you can have the right general problem but miss the mark on specific aspects of the problem
Architecture Prerequisite Buy versus build (market research) System architecture why was a particular architecture chosen? what things did we consider when we made our choices? (Cover your own butt) Major data structures Functionality Key algorithms that are present in the user requirements User interface Hardware requirements Nonfunctional Error processing Robustness Over engineering Fault tolerance Performance usually means the average response time, which is system dependant Strategy to handle changes
Without good software architecture you may have the right problem but the wrong solution. It may be impossible to have successful construction
Key Construction Decisions Choice of Programming Language Programming Conventions Your Location on the Technology Wave Selection of Major Construction Practices
Choice of Programming Language
Programming Conventions Allows for more productive coding between programmers on projects, as it provides a common platform from which the system is built. Before construction begins, spell out the programming conventions you'll use. Coding-convention details are at such a level of precision that they're nearly impossible to retrofit into software after it's written.
Your Location on the Technology Wave Programmers who program "in" a language limit their thoughts to constructs that the language directly supports. If the language tools are primitive, the programmer's thoughts will also be primitive. Programmers who program "into" a language first decide what thoughts they want to express, and then they determine how to express those thoughts using the tools provided by their specific language. Most of the important programming principles depend not on specific languages but on the way you use them