Data Flow Diagram (DFD)

DATA FLOW DIAGRAM

Data Flow Diagram (DFD) describes the system distribution into a smaller system. DFD allows the user to easily learn about computer and understand about worked system. DFD allows to learn new system are logically develop without consider the physically environment where the data flow (like by phone, mail, etc) or physically environment where the will be save (like file card, microfiche, hard disk, tape, diskette, etc). DFD is a tool used in methodology structured Analysis and design.

CONTEXT DIAGRAM

Context Diagram consists of one process to describe the system environment. It’s a highest level in DFD which is describes all the input into the system and output from system. System has a boundary which is to separate the system with the external entity. In context diagram there is no storage. Because context diagram are process to describe the system environment.

ZERO DIAGRAMS

Zero diagrams are describes the process of DFD. It gives a opinion spread all over the handled system, indicate the function or main process, data flow and external entity. This level enabled the data storage.

For no specific process in next level then add symbol ‘*’ or ‘P’ in the end of process. Balancing of input and output between Zero Diagram with Context Diagram always maintenance.

DETAIL DIAGRAMS

Detail Diagram is diagram which is explaining what kind of process in the zero diagrams or on the top level.

Numbering level in DFD:

Level Name	Diagram Name	Process Number
0	Context Diagram	-
1	Zero Diagram	1.0, 2.0, 3.0, …
2	Diagram 1.0	1.1, 1.2, 1.3, …
3	Diagram 1.1	1.1.1, 1.1.2, …

In one level at least seven processes and maximal nine process, if more than nine it must decomposition.

PROCESS SPECIFICATION

Each process in DFD must have process specification. Method in top level use to describe process with descriptive words. In detailed level that is lower process (functional primitive) need more structural specification.

Process specification will be a manual to programmer in create program or coding. Method in process specification is process scatter into story type, decision table, and decision tree.

EXTERNAL ENTITY

External Entity is entity in outside system environment which is like people, organization or others system in outside environment will give input or receive output from systems. External entity is uncounted part of the system. It symbolize with box notation.

 

Picture1. External Entity Notation

External entity can give identification with small letter in left top corner like bellow:

external entity example

Naming:

- Terminal name are noun words

- Terminal never have same name except the object are same.

DATA FLOW

Data Flow is place to flow the information. Describe with straight line that connected all the component of the system. Data flow showing with arrow and given name line or data flow.

This data flow stream between process, data store, and external entity and showing data flow can be input for the system or output system.

Picture2. Data flows are flow from consumer external entity into process of consumer orders it called consumer orders.

Guidelines to give a name:

- Data flow name consist of few flow words are connected with a line.

- No same of naming and the name should reflect its content.

- Data flow consists of few elements called element group.

- Avoid using word ‘data’ or ‘information’ to give a name in data flow.

- Possibly when write data flow name must complete write.

Other provisions:

- Data flow name put into a process may not be same as the data flow out of the process.

- Data flow are in or out from the data storage may not give name if:

o Simple data flow and easy to know.

o Data flow describes the entire data item.

- There is no data flow from terminal into data storage or the other way because terminal is not of part the system, connection between terminal and data storage must passed with process.

PROCESS

Process is activity or what is system do. Process can process the input data into output data. Process has a function to transformation one ore several input data into one or several output agree with the specification. Each process has one or several input along with creating one or several output. Process may be called bubble.

Physical Data Flow Diagram (PDFD), process can create by person, machine or computer. Logical Data Flow Diagram (LDFD) is a process just show process from computer.

Process Notation:

Picture3. Process notation in DFD

Guidelines to give a name:

- Process name consist of verbs an noun which reflects the function of the process.

- Never use word ‘processes’ as a part of name certain bubble.

- There are no several processes which have a same name.

- Process must have number. Numbering order possibility follow the flow or process orders, however numbering order means not absolutely as chronology process order.

DATA STORAGE

Data storage is place to store data on the system. Symbolize with a pair of horizontal parallel line with one of the side are opened. Process can take data from or give data into database.

Symbol of data storage:

 

Picture4. Data storage symbol.

Guidelines to give a name:

- Name must reflect the data storage

- If name more than one word then must give underscore.

DFD SYMBOLS

DATA DICTIONARY

Data Dictionary (DD) use to help system subject to define application detail and organize the entire data element which system use precisely until user and system analyst has same base interpretation about input, output, store and process. In analyst stage, dictionary data use as communication tools between system analysts with user. In system plan stage, dictionary data use to plan input, report, and database. Data flow in DFD are global, more detailed information seen on dictionary data.

Dictionary data contains:

- Data flow name: must write in order to all the reader who need more explanation about data flow can search easily.

- Alias: alias or other name from data can be written if the data are used.

- Data form: use to categorize dictionary data into application when system plans.

- Data flow: show from where data flow and where data goes.

- Explanation: give explanation about meaning from data flow.

DFD BALANCING

Data flow which enter into and out from one process must same with data flow which enter into and out from detailed process in lower level. Data flow name which enter into and out from one process must same as data flow name which enter into and out from detailed process. Amount and external entity name from certain process must same with amount and external entity name from that detail process.

The issues that must be considered in the DFD which have more than one level:

- Must have balance input and output between one level and next level.

- Balance between level 0 and level 1 seen in input or output from data flow go or from terminal in level 0, while balance between level 1 and level 2 seen in input or output from data flow go or from process concerned.

- Data flow name, data storage and terminal each level must same if the object same.

PROHIBITION IN DFD

- Data flow may not from external entity direct to external entity without through a process.

- Data flow may not from data storage direct to external entity without through a process.

- Data flow may not from data storage direct to other data storage without through a process.

- Data flow from one process direct to other process without through a saving data should or be avoided as much as possible.

EXAMPLE

Precision Tools sells a line of high-quality woodworking tools. When customers place orders on the company’s Web site, the system checks to see if the items are in stock, issues a status message to the customer, and generates a shipping order to the warehouse, which fills the order. When the order is shipped, the customer is billed. The system also produces various reports.

- Draw a context diagram for the order system

- Draw DFD diagram 0 for the order system

First we must identify Entities, Process, Data Stores, and Data Flow

* Entities

- Customer

- Warehouse

- Accounting

* Processes

- 1.0 Check Status

- 2.0 Issue Status Messages

- 3.0 Generate Shipping Order

- 4.0 Manage Accounts Receivable

- 5.0 Produce Reports

* Data Stores

- D1 Pending Orders

- D2 Accounts Receivable

      * Data Flows
          ** 1.0

– Order
– In-Stock Request
– Order Data

          ** 2.0

- Status Data

- Status Message

          ** 3.0
                – Shipping Order
                – Order Data
          **4.0

- Invoice

- Shipping Confirmation

- Payment

                  - Accounting Data
           ** 5.0
                  - Accounts Receivable Data

- Order Data

- Inventory Reports

Then draw Context Diagram of Order System

And draw Level-0 of Order System

There are several common modeling rules when creating DFDs:

1. All processes must have at least one data flow in and one data flow out.
2. All processes should modify the incoming data, producing new forms of outgoing data.
3. Each data store must be involved with at least one data flow.
4. Each external entity must be involved with at least one data flow.
5. A data flow must be attached to at least one process.
   
    reference : http://gedesanjaya.wordpress.com/2009/04/03/analysis-and-design-information-system-part-v/