Design Process
The design process involves the use of all the data collected during the analysis phase of the SDLC to create an appropriate design model. It is the key to an effective engineering process. It serves as a bridge between analysis and implementation. It defines the 'HOW' of the system, that is, how the system going to implement the expectations from it.

This tutorial contains:

The Design Model comprises of:

Design is an iterative process, during which requirements are translated into an outline for constructing the software. Certain characteristics  McGlaughlin has suggested three characteristics of a good design, which serve as a guide for evaluation of a given design. They are:
  • it must implement all the explicit requirements, and accommodate all the implicit requirements described by the customer
  • it must be a guide that is easily understood by those who write code, and for those who test and subsequently maintain the software
  • it should provide a complete picture of the software, addressing the data, functional and behavioral domains from an implementation perspective.

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Technical Criteria to establish a good design are:

  • it should exhibit a hierarchical organization that makes intelligent use of control among elements of software
  • it should be modular i.e. logically partitioned into elements that perform functions and sub-functions
  • it should contain both data and procedural abstractions
  • it should lead to interfaces that reduce the complexity of connections between modules, and the external environment
  • it should be derived using a repetitive method that is driven by information obtained during software requirement analysis

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The following are crucial for the effectiveness of a design process:

  • the problem defined must be examined from a number of view points and angles
  • a number of solutions must be identified to solve the problem 
  • the designer must make an appropriate choice after careful consideration of the pros and cons of each solution
  • each abstraction, each and every element, used in the solution must be described in detail    __ from the services it provides to the constraints it works under

The general tasks in the design process are:

  • designing the overall system processes
  • segmenting the system into smaller, compact workable modules
  • designing the database structure
  • specifying the details of the program to be created to achieve the desired functionality
  • designing the input and output documents
  • designing the controls for the system
  • documenting the system design
  • system reviews

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Data Design: The information domain model created during analysis is transformed into data structures necessary to implement the software.

Architectural Design: This will define the relationship among the major structural elements. It is derived from the interaction of subsystems within the analysis model.

Interface Design: This describes how the system interacts with the users, and with systems that interoperate with it.

Component-level Design: Here, structural elements of the programs architecture are converted into a procedural description of the software's components. Process Specification (PSPEC), Control Specification (CSPEC) and State Transition Diagrams (STD) provide the basis for procedural design.

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