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Design

"Measure twice, cut once."

The last 20-30 years of software engineering literature heavily emphasize the importance of "application design" during software development.  "Design" is the high-level plan for structure and interactions of components planned for the final system.

Despite this, many programmers have never used a high-level logical diagram, a logical data model, etc. - some of the most commonly employed design tools.

Our experience has been that a well-formulated design streamlines product construction.  Good design products reduce construction "rework" by ensuring that high-level logic and interactions are well planned before programming is started. The benefits during implementation typically match or exceed the additional costs associated with the design work.

Rigorous design efforts typically delay the onset of implementation work (programming, etc.) slightly, but result in:

• a much faster implementation phase
• major reductions in unexpected problems
• a more steady, predictable rate of progress during programming
• enhanced ease of maintenance for final products  

Programmers frequently find that they have a more sure understanding of how components of the solution interact - this translates into cleaner, better structured programs. 

Typically, our product designs are generated using the products of system analysis as input.

Design products

• Context Dataflow Diagram - dataflow diagram documenting the major information flows into, through, and out of the system
• Elaborated Use Case Descriptions - use case descriptions elaborated to specify exact mechanisms used for user interface elements, etc.
• Forms Navigation Model - flowchart outlining main navigation paths provided to the user. (form navigation model example 1 form navigation model example 2)
• Modularization Plan - outlines high-level structure of the system. This typically will include a description of user interface objects, their functions, and their interactions. (modularization plan example 1, modularization plan example 2, modularization plan example 3)
• Naming Conventions - outlines proposed system for constructing names for files, tables, columns, etc. within the new system. (naming conventions example)
• Physical Data Model Diagram - diagram outlining the proposed actual storage of information in the selected software/hardware platform. This will sometimes differ from the detailed data model developed in analysis stage in order to take full advantage of features of the selected software/hardware platform.
• Process Diagrams - (Typically used only for complex proceses) detailed diagrams representing the logic flow and data movement of the process as supported by the system. (proposed process dataflow example)
• Selected Development Platform - describes final choice of software database managemetnt system, programming languages, computer hardware, etc.

Process

Involvement of client staff representatives begins to decrease in design stage. The development team typically spends more time on their own converting the business and user requirements of earlier work into a viable system design. Client staff may still be involved in reviews of interface mockups, questions about details accidentally overlooked in earlier requirements work, or in providing a user perspective about alternative approaches being considered.

Last modified: 12:33:37 23-Jan-2009