Friday, September 28, 2012

Quality checking of DFD

  • Correctness checking determines that the syntax and connections used in diagrams, charts, and so forth are  accurately used. 
  • Completeness checking is  performed with the  users  to  validate  the  meanings  of  all  terms and to verify the semantics used in all documentation.  
  • Consistency  checking  ensures  consistency  and  correctness  of  all  entries  that  span multiple diagrams, text, charts, and so on.  Consistency  checks  evaluate  the  interitem  syntax  and semantics. These checks are first performed by the project team during walk-throughs or other quality assurance evaluations. Then, they may be reviewed by  independent  quality  assurance  analysts  as  an added check. 

Sumber: Conger, 2008

Decompose Level 0 to Level 1

For each Level 0 process,

  1. Draw the input and output flows  and the icons to which they connect from the higher level diagram. This forms the skeleton of the diagram. These are called the net  inflows and outflows. 
  2. Define the subprocesses by asking, "What are the steps required to do this process?" Then for each step, "Can I separate this from the other steps and do  it in isolation?" For each subprocess you isolate,  draw a process rec-tangle on the lower level diagram. 
  3. Identify whether data stores are required or not. Add them and, if they are new,  name them. 
  4. Identify data flows  to complete the diagram.  Make sure you provide all and only the information required to perform the process. 
  5. Review the diagram for unnecessary connec-tions and,  if found,  remove them. 
  6. Update the  data dictionary with all new information.

Sumber: Conger, 2008

Friday, September 21, 2012

Identify the Level 0 processes

  • Identify the Level 0 processes that are  within the circle of the context diagram, without defining any data stores.
  • The difficulty of this activity varies with your understanding of the problem domain and the  scope of the project.
  • After the processes are  identified, next define file locations  on  the  Level  0  data flow  diagram.  
  • You could  leave  files  for  a  lower  level  of analysis  as many texts and companies do by convention. In that case, you are ready to  draw the diagram.  
  • To  identify data stores, first consider each process.  
  • Can the process be completed without reading or writing to a data store? 
  • If your answer is yes, then you do  not need a file  at this level. 
  • If the answer is no,  you need one data store for every required read action and every required write action.  
  • Many times, the reads and writes are to the same data store. Then, you have one data flow per input/output action. 
  • As these required reads and writes are identified, you add to the DFD to  include the data store name and data flow(s).  
  • When you do  this part of the drawing, make sure that each flow  and store has a name. 

Level 0 Syntax Rules:
  1. All processes are connected to something else. 
  2. All process have both inputs and outputs. 
  3. No processes have only outputs or only inputs. 
  4. Processes may connect to  anything:  other processes, data stores, or entities. 
  5. All processes have a unique name and number. 
  6. Each process number is used once in the diagram set. 
  7. Only subprocesses of a process shall follow the numbering scheme of the parent process. 
  8. Entities and data stores may connect only to processes. Another way to state this is that each data flow must have at least one end connected to  a process. 
  9. Data flows  are the only legal type of connection between entities, processes, and data stores. 
  10. Make sure there are no  dangling arrows. 
  11. The net data flows  to  and from context diagram external entities must balance, that is, be present, in each level of DFDs. 
  12. Trivial errors and exceptions are  not handled until L1 or lower in the DFD set. 
  13. Trivial data stores show up in the diagram set the first time they are referenced by a process. 
Sumber: Conger, 2008

Friday, September 14, 2012

Data Flow Diagram

  • A data flow diagram (DFD) is a  graphic representation of the application's component parts. 
  • The entities and data flows  from  the  context diagram are  all  present ini DFD.  
  • Data flows may connect processes to other processes,  data  stores,  or  external  entities.  
  • Data stores and external entities do not interact directly with each other. 
  • All entities and data flows from the higher level processes must be in every more detailed diagram.  The names of entities and data flows must be consistent across the levels of the  diagrams

DFD Rules:
  1. Define the processes. 
  2. Define the files  and other data flows  required to support the processes. 
  3. Draw a Level 0 DFD. At level 0,  ignore trivial error paths and data stores. If you define a validation process, you must eventually identify an error path.  Define the error path at the primitive level. Similarly for data stores, define files  when they are shared between processes. Introduce files  that are only used within a given process at the level at which the file  is shared between two or more subprocesses.
  4. Balance the DFD with the context diagram. Compare the net inputs and outputs to external entities on the DFD to the net inputs and outputs on the context diagram. There should be a one-to-one correspondence between the diagrams. 
  5. Iterate through this procedure until the primi-tive level of DFD is reached for  all processes. Always balance the current level DFD's net inputs and outputs with those of the previous level.
Sumber: Conger, 2008