Structured Analysis

21:09 Prashant Roy 0 Comments

Structured  Analysis


Sructured analysis is a developement method for the analysis of existing ,manual or automated systems,leading to the development of specifications for a new or modified system.Stuctured analysis allows the analyst to learn about a system or a process in a managable and logical way.
The objectives in structural analysis is to completely is to completely understand the current system from which requirements are determined. The aim of structured analysis is to clearly define what systems requirements are.

Components of stuctured anaysis:
  1. Graphical Symbol
  • Icons
  • DFD(Data Flow Design)
     2. Data Dictionary
     3.Procedure and process description
     4.Rules:These are standards for describing and documenting the system correctly and completely
     good documentation will provide an explanation of a how a system operates.

Data Flow Analysis:


 System analysis is basically centerd arround:
  • What process make up a system.
  • What data are used in each process of the system.
  • What data is stored.
  • What data enter and leave the system.

Data Flow Diagram(DFD)

Data Flow Diagram(DFD) is a graphical tool.It is used to describe and analyse the movement of data through a system manual or automated.They focus on the data flowing into the system , betweenprocesses and in and out of the datastores.
This is a central tool and the basis from which other components are developed . The system models are termed as data flow diagram(DFD).Developing a description of the system using structured analysis follows a top down process.Each process can be broken down intp the more detailed DFD.

Types of  DFDs:

There are two tyes of DFD:
  1. Physical DFD
  2. Logical DFD
1)Physical DFD: The physical DFD is a model of the current system and is used to ensure that the current system and is used to ensure that the current system has been clerly understood.Physical DFDs shows actual devices,departments,people etc. involved in the current system.
2)Logical DFD:The logical DFDs are the models of the proposed system.They should clearly show the requirements on which the new system should be built.Later during design activity this is taken as the basis for drawing the systems structure charts.
Note: Both physical and logical DFDs support a top down approach to system analysis.

Drawing Data Flow Diagrams:

Notation:
DFDs are quite easy to read and understand.There are two alternative but equivalent symbol set
  1. Yardon symbol set
  2. Gane-sarson symbol set
It is suggested that you do not mix and match symbol sets.Four simple notations are sufficient to complete a DFD.They are:
  • Data Flow
  • Process
  • External entities
  • Data Store
Explanation of Notation:
  1. Data Flow:Data in a system move in a specific direction that is from origin to destination.The data flow is a "packet" of data indicating the movement of data within the system. Data flow must be inputs to or output from processes. They must contain data and all data flows should  be labbled indicating what data is flowing.If data flow is showing an input then the arrow should point towards the process, but in case the data flow is showing an output then the arrow should point away from the process.
Data flow symbol

  1. Process:Processes are work or action that are performed by people, machines or computers on incoming data flows to produce outgoing data flows. The details of the processing that is the logic or producers are not represent in a DFD.Each process should be given a meaningful name.
Data Process symbol

  1. External entities:External entities are organizations, other information systems, departments or people which represent a source or destination of transactions or data when the system we are cosidering accepts data from another system or provides data to it,that other system is external entities."External entity represents any entity that supplies or recieves information from the system but is not a part of the system."
External entities symbol

  1. Data Store:Data stores could be thought of as the memory of the system.A data store must have atleast one data flow pointing towards it, or one away from it The data store must have a lebel which is placed between the two parrallel lines.The levels of data stores must be nouns and must clearly identify what the data store contains as a class of objects.
Data Store symbol

Advantage of DFD:

  1. It aids in describing the boundaries of the system.
  2. It is beneficial for communicating existing system knowledge to the user.
  3. A straightforward graphical technique which is easy to recognize.
  4. DFDs can provide a detailed represantaion of system component.
  5. It is used as the part of the system documentation file.
  6. It is easier to understand by technical & non technical audiences.
  7. It supports the logic behind the data flow within the system.

Disadvantage of DFD:

  1. It makes the programmers littile confusing concerning the system.
  2. The biggest drawback of DFD is that it simply takes a long time to create ,so long that the analyst may not recieve support from management to complete it.
  3. Physical considerations are left out.

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