DFD is a logical data model or process that is made to describe the origin of the data and the destination where the data out of the system, where data is stored, the process that produces the data and the interaction between the data stored and the process is imposed on data.
DFD are often used to describe a system that already exists or the new system will be developed logically without considering the physical environment where the data flows, or where data are stored and the user is less easy to understand to understand the field of computer systems that will be done.
Context Diagram
the top level diagram, a diagram of a system that describes the stream-flow data that enter and exit the system and the incoming and
out of the foreign entity
The case must be considered:
Provide a snapshot of the entire system
Terminals that provide input to system called source
Terminal that receives the output called sinks
Only one process
Consists of a process and describe the scope of a system
Is the highest level of the DFD that describes the entire system to the input of the system and output
System is limited by Boundary (depicted by broken lines)
No storage (storage)
how to create a context diagram
Specify the name of the system.
Determine the limits of the system.
Specify the terminator is present in the system.
Define what is received / given terminator from / to the system.
Describe context diagram.
Zero Diagram
After making context will proceed with the making of:
DFD level 0 context diagram is a representation of more detailed (overview diagram) and to give a view on the overall system in which, showing the main function or process that is, the flow of data and entity external
It should be:
At this level of data storage possible
To process that does not detail again on the next level then added to the symbol '*' or 'P' at the end of the process
Balance of input and output (balancing) between 0 to diagram context diagram should be maintained
how to create a zero diagram:
Determine the main process in the system.
Determine what is given / received each process to / from the system while considering the concept of balance (the data flow outgoing / incoming from a level should be the same as the flow of data entry / exit to the next level).
If necessary, store a feature data (master) as the source and destination flow data.
describe diagram level zero.
- Avoid intersection flow data
- Give the number on the main process (the number does not indicate the order process).
Detailed Diagram
is diagrams that decompose a process that is in the diagram zero level or above
Numbering level in the DFD:
In one level there should be no more than 7 units and the maximum of 9, when more should be done in the decompositionDFD level 1:
Each process level 0 will described the details must be observed:
�� balance the flow of data between zero diagram and detailed diagrams In the process
�� not detail again, add a sign * at the end of the numbering process Balance
�� data store used
How:
Define the process of smaller (sub-process) from the main process in the zero level.
Determine what is given / received each sub-process to / from the system and note the concept of balance.
If necessary, store a feature data (transaction) as the source and destination flow data.
One describe level DFD
- Avoid intersection flow of data.
- Give the number on each sub-process that shows the decomposition of the process before.
Example: 1.1, 1.2, 2.1
SPECIFICATION PROCESS
Each process in the DFD must have a specification process
At the top level method is used to describe the process can use a sentence with descriptive
At a more detailed level, namely on the bottom (functional primitive) requires specification of a more structured
Specification process will be the guideline for the programmer to make this program (coding)
Method used in the specification process: the process of disintegration in the form of a story, decision table, decision tree
ON FOREIGN (foreign entities)
Foreign entity is the entity that is outside the system that provides data to the system (source) or receive information from the system (sinks) that are in the outside environment that will provide input or receive output from the system. Foreign entity is not part of the system, when an information system designed for one section / department and other parts that are still related to a foreign entity. While the terminal is the entity that is part of the system.
Something that is outside the system, but it provides data in the system or to provide data from the system
for example:
- An office, department or division within the company but outside the system being developed.
- The person or group of people in the organization but outside of that system is being developed.
symbolized with the notation
External entity not part of the system including
Naming:
The name of the form of noun
Terminal may not have the same name except the same objeknya
CASH DATA
Is the place to make a flow an information
Depicted with the straight line that connects the components of the system
Data flow direction is indicated with arrows and lines give the name on the flow of data that flows
Flow data flow between processes, data storage and data flow indicates that the form of data input for the system
Data flow describes the flow of data from one entity to another entity. The direction the arrow depicts the flow of data. There are several streams of data, namely:
• Between the two processes in sequence
• from data storage (data store) to the process and vice versa
• From the source to the process
• From the process to sink
Guidelines of the name:
Name of the flow of data that consists of some words associated with the flow lines connect
No flow data for the same and the name should reflect its content
The flow of data that consists of several elements can be expressed with the group element
Avoid using the word 'data' and 'information' to give a name to the flow of data
Wherever possible the complete flow of data is written
Other provisions in the current data:
Name of the flow of data into a process may not be the same as the name of the data flow out of the process
Data flow into or out of data storage does not need to be given a name if:
The flow of data simple and easy to understand
Describes the data flow of all data items
There can be no flow of data from the terminal to the data storage, or vice versa because the terminal is not part of the system, the relationship with the terminal data storage must be through a process
PROCESS
Describe what the process done by the system. Transform function of one or more of data input into one or more of the output data in accordance with the desired specifications. Each process has one or more data inputs and generates one or more output data. The process also often called bubble. For Physical data flow diagrams (LDFD), the process can be done by a person, machine or computer and for Logical data flow diagram is a process only shows the process of computer
Symbols used: circle
Guidelines of the process:
Name of the process consists of a verb and noun, which reflects the function of the process
Do not use the process as part of the name of a bubble
May not have some process that has the same name
The process should be given a number. Order number wherever possible to follow the flow of the process or sequence, but the sequence number does not mean that the absolute is a process in chronological order
Data Storage
Data storage is a storage place for data that exists in the system
symbolized with a pair of parallel lines or two lines with one side open side
The process can retrieve data from or provide data to the database
Savings can be the following data:
1.file or database in the computer system
2.manual record keeping or
3.the data in a table
4.table reference manual
5. agenda book
Guidelines of the name:
The name should reflect the data storage
When his name more than one word must be marked with the number
DFD Symbols
Dictionary of Data (Catalog Data)
Is a catalog (storage) of the elements that are in a system. Data dictionary has the same function in modeling the system and also help the system to understand the application in detail, and organize all elements of the data used in the system so that users and analyze system have basic understanding about the same input, output, storage and processing.
Data dictionary defines the data elements with the function as follows:
1. Explain the meaning of the data flow and storage in the DFD
2. Describe your composition package moving through the data flow to be described, for example address city, state and zip code
3. Describe your data storage composition
4. Specify the value and the relevant unit for the storage and flow and
5. Describe your relationship between the details of storage that will be the focus point in the diagram entity relationship
Working data dictionary to help the system to interpret the application in detail and organize all elements of the data used in the system precisely so that the system analyst and have a basic understanding of the same input, output, storage and process
At analysis, the data dictionary is used as a means of communication between the systems analyst with the
At the system design, data dictionary is used to design input, reports and databases
Flow data on the global DAD, further details can be seen in the data dictionary
Load the data dictionary as follows:
Name of data flow: must note that readers who need further explanation about a flow of data can find it easily
Alias: alias or other name of the data can be written when there is
Forms of data: used to segment the data dictionary to use when designing the system
Flow data: indicates from which data flows and where the data
Description: to give an explanation of the meaning of the data flow
Balancing IN DFD
The flow of data into and out of a process must be the same as the flow of data into and out of the details of the process on the level / levels below
Name of the data flow into and out of the process must match the name of the flow of data into and out of the details of the process
Number and the name of an entity outside the process must be equal to the number of names and entities outside of the details of the process
The issues that must be considered in the DFD which have more than one level:
There must be a balance between input and output of one level and next level
Balance between level 0 and level 1 at the input / output of stream data to or from the terminal on level 0, while the balance between level 1 and level 2 is seen on the input / output of stream data to / from the process concerned
Name of the flow of data, data storage and terminals at each level must be the same if the same object
Restrictions in DFD
Flow data may not be from outside the entity directly to other outside entities without going through a process
Flow data may not be from the savings directly to the data to outside entities without going through a process
Flow data may not be saving the data directly from the savings and other data without going through a process
Flow data from one process directly to the other without going through the process of saving data should / be avoided as much as possible
No comments:
Post a Comment