Logical Design

Analysis and Design

The Guide describes one analysis phase and two design phases, a logical phase and a physical phase. The analysis phase takes the problem domain apart and identifies it’s components, the design phases assemble the solution. From the business point of view the Logical Design phase is where the ‘Top Be’ model of the solution is described and may involve Business Process Re-engineering (BPR).

Logical Design
Logical Design

Logical design involves taking user requirements and the information from the analysis phase and producing a design for the solution. The design should be understandable to both stakeholders and technical staff; although there will be variability in levels of understanding. This phase will produce specifications and models for the functions needed to satisfy the requirements.. At this stage the project plan will be used to allocate work and will be reviewed in the light of the work products of this phase. The work products should include the outputs from the design methodology, for example use case specifications, context diagram, data flow diagrams, state-transitions, entity relationships and process specifications. Common business functionality will be identified at this stage.


Work Products


Logical Design will normally be done in a top-down fashion with the initial direction determined by the business imperative. The initial statement of design should identify how the project intends to improve either the business process or the way that the IT system addresses the business process. This should be a verifiable proposition as defined in the cost/benefit analysis.

The inputs to design include requirements may include a new business process or may have a combination new processes and enhancements. The design process must verify that all the business requirements will be met by the new design.

The outputs from this stage should be the normal outputs from a design methodology with some products optional such as specific diagram types such as state-transition diagrams.

The System Architecture will describe the scope and the overall functionality of the system this document should complement the Context Diagram and the Level 0 Data Flow Diagram. The System Architecture should be available for early review so that it can be used to ensure that the system being designed has the correct scope and function.

Design Attributes:

  • Efficiency
  • Elegance
  • Usability
  • Coverage
  • Clarity
  • Flexibility

Scope of Design

It should be noted that it is not necessary to complete Logical Design for the whole solution as a single task. It may be advantageous to describe a broad architecture and then address that part of the solution which will yield the most immediate benefit. In this way the design process itself will have its own context and scope, and may be repeated until the whole solution has been designed.