It is a set of design steps that allows a DFD with transforms flow characteristics to be mapped into a specific architectural style. In transform, mapping is described by applying design steps to an example system a portion of the safe home security software. The Safe Home security system is representative of many computer-based products and systems in use today.
The product monitors the real world and reacts to changes that it encounters. It also interacts with a user through a series of typed inputs and alphanumeric displays. During requirements analysis, more detailed flow models would be created for SafeHome. In addition, control and process specifications, a data dictionary, and various behavioral models would also be created.
The Proceeding example will be used to illustrate each step in transform mapping. The steps begin with a re-evaluation of work done during requirements analysis and then remove to the design of the software architecture.
step 1: Review the fundamental system model
The fundamental system model encircles level 0 DFD. In actuality, the design step starts with an evaluation of system specification and software requirements specification. Both documents describe information flow and structure at the software interface.
step 2: Review and refine data flow diagrams for the software
Information contained in the requirements specification can be obtained from analysis models is refined to produce greater detail.
For example, level 2 DFD for monitor sensors is examined at level 3, each transform in the data flow diagram exhibits relatively high cohesion. That is, the process implied by a transform performs a single, distinct function that can be implemented as a module9 in the safe home software.
step 3: Determine whether the DFD has flow characteristics
In general, information flow within a system can always be represented as transformed. In this step, the designer selects global flow characteristics based on the prevailing nature of the DFD. In addition, local regions of transform or transaction flow are isolated.
step 4: isolate the transforming center by specifying incoming and outgoing flow boundaries
In incoming flow a path in which information is converted from external to internal form, outgoing flow converts from internal to external form. Incoming and outgoing flow boundaries open to interpretation. That is different designers select slightly different points in the flow as bounded location.
Alternative design solutions can be found by the vary of flow boundary placements. A variance of 1 bubble along a Floor pass will generally have little impact on the final program structure, even care should be taken when boundaries are selected. An argument can be made to read a boundary. The emphasis in this region still should be selecting reasonable boundaries, rather than length iteration and displacement of divisions.
Step 5: perform first-level factoring
Program structure describes a top-down distribution of control. Factoring outcomes in a program structure in which top-level modules perform decision making and low-level models perform most input, computation, and output work. Middle-level modules perform some control and do a moderate amount of work.
When transform close encountered, a DFD is mapped to a specific structure and provides a control for incoming, transform, and outgoing information processing. The main controller resides at the top of the program structure and co-ordinates the following subordinate control functions.
The number of models at the first level should be limited to the minimum that can complete control functions and still maintain good coupling and Cohesion characteristics.
step 6: Perform second level factoring
Second level factoring is achieved by nothing individual transforms of a DFD into relevant modules within the architecture. Beginning at the transform center boundary and going outward allowing incoming and outgoing paths, transforms are mapped into subordinate levels of the software structure, practical points, and standards of design quality deliver the outcome of second-level factoring.
Second level factoring for incoming flow in the same manner. Factoring is again accomplished by moving outward from the transform center boundary and the incoming flow side. The transform center off monitor sensor subsystem software is map somewhat differently. Each of the data conversion or calculation Transforms of the transform portion of the DFD is mapped into a module subordinate to the transforming controller.
Information that moves into and out of the module. Data that is retained by a module, data stored in a local data structure. A procedural narrative that intimates major decision points and tasks. The narrator labors as a first-generation design specification. However, further refinement and editions happen regularly during this period of design.
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