OOAD Object Modeling Techniques Q/A #3

Question:What is JSD? Explain this design with its advantages and disadvantages.

Answer:

JSD, Jackson Structure Design is a methodology to specify and design systems in which time factor is significant and system may be described using sequence of events. Developed by Michael A. Jackson , this design method considers the fact that the design of the system is an extension of the programme design. The purpose of this design method is to create a maintainable software. The method addresses all stages of the software development life cycle. It has three phases:

1. Modeling phase - A JSD model starts with real world consideration. This phase is a part of analysis process. The aspects of the real world relevant to the system being developed are modeled in this phase.

2. Specification phase - This phase focuses on the specification. In this phase JSD determines what is to be done? The previous phase i.e. the modeling phase provides the basic for the system specifications to achieve the required functionality.

3. implementation phase - In this phase , JSD determines how to achieve required functionality. Operational specifications are executed so that it expresses desired system behavior in terms of some abstract machine.

Ways of working

• The basic principle of operation of JSD is that development must start with describing and modeling the real world rather than specifying the function performed by the system.

• The second principle states that an adequate model of a time ordered world must itself be time ordered. The aim is to map progress in the real world on progress in the system that models it.

• The third principle stetes way of implementing the system based on transformation of specification in to efficient set of processes. These processes should be designed in a manner to make them run on available software and hardware.

Steps for JSD software development

Originally presented by Jackson in 1983 the method consisted of six steps which are following.

1. Entity /action step

2. Entity structure step

3. Initial model step

4. function step

5. system timing step

6. system implementing step

Later , some steps were combined to create a method with only three steps

1. Modeling stage (Analysis)

   • Action step

   • Structure step

2. Network stage (design)

   • Initial model step

   • Function step

   • System timing step

3. Implementation stage (Realisation)

   • System implementation step

Advantages of JSD

1. specially designed to handle real time problem.

2. JSD considers concurrent processing and timing.

3. JSD modeling focuses on time.

4. It provide functionality in the real world.

5. Excellent methodology for micro code application.

Disadvantages of JSD

1. JSD is a poor approach for high level analysis and data base design.

2. More complex due to pseudo code representation.

3. complex and difficult to understand.

4. less graphically oriented than SA/ SD and OMT.