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Structured Design is a method to convert an ''informal specification'' including a set of data flow diagrams and process specifications into a design that could be implemented using a language like Pascal or C. It was developed by Edward Yourdon and Larry Constantine, reportedly by examining a number of systems that had been developed in the 1960 's that were regarded as good design examples, and identifying common features and patterns that they contained. Structured Design does not produce designs that have a number of desirable properties: It doesn't take advantage of the newer features provided by object-oriented programming languages. While structured design provides some limited support for ''encapsulation of data'' (information hiding) it doesn't really support inheritance or templates, so it doesn't help you to take advantage of opportunities for reuse of software.
It doesn't produce designs that are suitable for ''highly interactive''s ystem's - that is, systems which the user interacts with the system using a mouse as well as a terminal, so that the user has more control over the order in which things are done, than is generally provided by systems that use a ''command line'' interface, or that rely on simple menus that could be used with a terminal, rather than on a workstation or PC running a windowing system. These simpler interfaces (command line, and simple menu based ones) were the only ones in widespread use when this design method was developed. It doesn't produce designs that are useful for real time systems, or other systems in which performance requirements play a greater role than they do in more traditional business systems. We will continue to assume, as is still usually the case, that it's sufficient (and therefore appropriate) to design and implement without much consideration of performance requirements - and, after that, we " ll perform tests that include ''performance tests, '' in order to look for evidence that resource requirements haven't been met, find bottlenecks, and then recode (and possibly also redesign) where needed.
It doesn't lead to innovative or elegant designs. Techniques like these can be used to deal with the 90 % (or more) of the system that is routine - just like most of the same systems that solve this kind of problem - and that can be dealt with well enough using straightforward, conventional methods. The use of this kind of method will (arguably) free up more of your time for those parts of the problem that do require innovation or expertise. However, Structured Design does provide usable, maintainable designs for the type of programs (and programming languages) it supports.
As well, highly interactive and real time systems often include subsystems that can be developed using this older method, so it may still be useful. Finally, some of the ideas we " ll see by studying this method have been carried forward into some of the more modern design techniques. The newer methods are more complicated and not (yet) as well described as Structured Design, so (one hopes that) this is a useful ''example of a design method'' to study before considering a more modern one. Structured Design is discussed in Pressman's text, Software Engineering: A Practitioner's Approach.
Another more detailed (and very readable) reference is the book by Page-Jones which is on reserve in the library: The Practical Guide to Structured Systems Design Second Edition, Prentice Hall (Yourdon Press), 1988 Structured Design can be used to convert a set of data flow diagrams and process specifications into a design specification that includes a structure chart, which shows the system's modules and data areas, their control structure, and the I/O between them; a module specification for each of the modules in the structure chart (as well as for the interface for each data area). More will be said about module specifications later on; we " ll start by considering the components of a structure chart. A module corresponds to a single function or procedure in a language like FORTRAN or Pascal, or to a single function in C or C++ (but, not generally to an ''object'' or "''class'' in C++). A module is drawn as a rectangle, labeled by the module's name - which should also be a reasonable name for a function or procedure (or, occasionally, subsystem) in the program being developed. Here are two examples. The above notation is used to represent modules for procedures we " ll need to develop ourselves.
It's also useful (or necessary) to show ''library modules'' that are part of the operating system (or windowing system, or, more generally, software library or libraries) that supports the system we " re developing - that is, modules that we don't need to develop ourselves. An extra vertical bar on each side of the rectangle is used to identify these: A structure chart includes one main module - the module at the top of the structure chart, which corresponds to the ''main'' part of the program being produced. Each module is connected to all the modules that it calls directly. This connection is shown by having an arrow pointing from the calling module to the module it can call. This design technique doesn't seem to introduce recursive functions (by itself). However, you certainly might add these as you improve the structure chart at the end of ''architectural design, ''s o you might end up drawing an arrow that connects a module to itself, etc.
A structure chart also include representations of ''data areas. '' In the ''first draft''s structured charts that we obtain at the beginning of structured design, we " ll draw a data area by listing the data area's name between two horizontal lines: However, the time the structure chart has been completed, we will have identified a set of interface functions used for all communication between the data area and the rest of the system - that is, we should have completed at least the beginning steps of data design. At that point, the data area (also now called a...
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