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商業(yè)企業(yè)的購銷存管理信息系統(tǒng)的設(shè)計與實現(xiàn)-資料下載頁

2025-04-12 05:58本頁面
  

【正文】 ence for the development team.DesignWhen you are doing design, you can get more technical with your diagrams. You can use more notation and be more precise about your notation. Some useful techniques are:Class diagrams from a software perspective. These show the classes in the software and how they interrelate.Sequence diagrams for mon scenarios. A valuable approach is to pick the most important and interesting scenarios from the use cases and use CRC cards or sequence diagrams to figure out what happens in the software.Package diagrams to show the largescale organization of the software.State diagrams for classes with plex life histories.Deployment diagrams to show the physical layout of the software.Many of these same techniques can be used to document software once it39。s been written. This may help people find their way around the software if they have to work on it and are not familiar with the code.With a waterfall life cycle, you would do these diagrams and activities as part of the phases. The endofphase documents usually include the appropriate UML diagrams for that activity. A waterfall style usually implies that the UML is used as a blueprint.In an iterative style, the UML diagrams can be used in either a blueprint or a sketch style. With a blueprint, the analysis diagrams will usually be built in the iteration prior to the one that builds the functionality. Each iteration doesn39。t start from scratch。 rather, it modifies the existing body of documents, highlighting the changes in the new iteration.Blueprint designs are usually done early in the iteration and may be done in pieces for different bits of functionality that are targeted for the iteration. Again, iteration implies making changes to an existing model rather than building a new model each time.Using the UML in sketch mode implies a more fluid process. One approach is to spend a couple of days at the beginning of an iteration, sketching out the design for that iteration. You can also do short design sessions at any point during the iteration, setting up a quick meeting for half an hour whenever a developer starts to tackle a nontrivial function.With a blueprint, you expect the code implementation to follow the diagrams. A change from the blueprint is a deviation that needs review from the designers who did the blueprint. A sketch is usually treated more as a first cut at the design。 if, during coding, people find that the sketch isn39。t exactly right, they should feel free to change the design. The implementors have to use their judgment as to whether the change needs a wider discussion to understand the full ramifications.One of my concerns with blueprints is my own observation that it39。s very hard to get them right, even for a good designer. I often find that my own designs do not survive contact with coding intact. I still find UML sketches useful, but I don39。t find that they can be treated as absolutes.In both modes, it makes sense to explore a number of design alternatives. It39。s usually best to explore alternatives in sketch mode so that you can quickly generate and change the alternatives. Once you pick a design to run with, you can either use that sketch or detail it into a blueprint.DocumentationOnce you have built the software, you can use the UML to help document what you have done. For this, I find UML diagrams useful for getting an overall understanding of a system. In doing this, however, I should stress that I do not believe in producing detailed diagrams of the whole system. To quote Ward Cunningham [Cunningham]:Carefully selected and wellwritten memos can easily substitute for traditional prehensive design documentation. The latter rarely shines except in isolated spots. Elevate those spots . . . and forget about the rest. I believe that detailed documentation should be generated from the code—like, for instance, JavaDoc. You should write additional documentation to highlight important concepts. Think of these as prising a first step for the reader before he or she goes into the codebased details. I like to structure these as prose documents, short enough to read over a cup of coffee, using UML diagrams to help illustrate the discussion. I prefer the diagrams as sketches that highlight the most important parts of the system. Obviously, the writer of the document needs to decide what is important and what isn39。t, but the writer is much better equipped than the reader to do that.A package diagram makes a good logical road map of the system. This diagram helps me understand the logical pieces of the system and see the dependencies and keep them under control. A deployment diagram, which shows the highlevel physical picture, may also prove useful at this stage.Within each package, I like to see a class diagram. I don39。t show every operation on every class. I show only the important features that help me understand what is in there. This class diagram acts as a graphical table of contents.The class diagram should be supported by a handful of interaction diagrams that show the most important interactions in the system. Again, selectivity is important here。 remember that, in this kind of document, prehensiveness is the enemy of prehensibility.If a class has plex lifecycle behavior, I draw a state machine diagram to describe it. I do this only if the behavior is sufficiently plex, which I find doesn39。t happen often.I39。ll often include some important code, written in a literate program style. If a particularly plex algorithm is involved, I39。ll consider using an activity diagram but only if it gives me more understanding than the code alone.If I find concepts that are ing up repeatedly, I use patterns to capture the basic ideas.One of the most important things to document is the design alternatives you didn39。t take and why you didn39。t do them. That39。s often the most forgotten but most useful piece of external documentation you c
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