Data Flow Diagram (DFD)

Data Flow Diagram

DEFINITION
Data flow diagram is a well known approach to visualize the data processing in business analysis field. A data flow diagram is strong in illustrating the relationship of processes, data stores and external entities in business information system.

ZERO DIAGRAM

- Describe the process of the DFD

- Provide views on the overall system in which, showing the main function or process that is, the flow of data and entity eskternal

- At this level of data storage possible

- For processes that do not detailed again on the next level then added the symbol '*' or 'P' at the end of the process

- Input and output balance (balancing) between 0 to diagram context diagram should be maintained

The goal of zero diagram is to “break down” a system to “processes” that must be done ‘in person’. Or, if made in the sentence is: “What is the process that must be done in order to reach the system?.”
Thus, this diagram is the continuation of the context diagram, which “extend the circle,” and for (the number and content) and the terminator (the amount and content) data flow to and from the terminator should be fixed.

DETAILED DIAGRAM
Diagram is a detailed diagram of the process of decipher what is in a chart or diagram zero level above.

Numbering level in the DFD:

Level Name	Diagram Name	Process Number
0	Context
1	Diagram 0	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, …

EXTERNAL ENTITIES

Something that is outside the system, but it provides data into the system or providing data from the system, is represented with a notation box. External entity does not include part of the system. When the information system is designed for one section (department) then the other part that is still a relevant external entity.

Guidelines of external entities:

- The name of the form of noun
- Terminal may not have the same name unless the object is the same (described twice, is intended to make the diagram more clear). If so, then the terminal should be a forward slash in the top left corner.

SPECIFICATION PROCESS

- Each process in the DFD must have a specification process.

- At the top level method is used to describe the process you can use with descriptive sentences.

- At a more detailed level, namely on the bottom (functional primitive) require a more structured specification.

- 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.

DATA FLOW

Flow data consist of a group of related data elements in a logical move from one process to another process.

- Depicted with a straight line connecting the components of the system.

- Flow data is shown with the direction arrows and the name on the flow of data that flows.

- Cash flow of data between processes, saving data, the unit outside, and shows data flow from data in the form of inputs to the system.

- Guidelines of the name:

1. Name of the flow of data that consists of some words associated with the flow lines connect.

2. No flow data for the same and the name should reflect its content

3. The flow of data that consists of several elements can be expressed with the group element

4. Avoid using the word 'data' and 'information' to give a name to the flow of data

5. Wherever possible the complete flow of data is written

6. 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

7. Data flow into or out of data storage does not need to be given a name if:
- Flow of data simple and easy to understand
- Flow of data describes all data items

8. 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 the process.

PROCESS

Logical process models omit any processes that do nothing more than move or route data , thus leaving the data unchanged.

Valid processes include those that:

· Perform computations (e.g., calculate grade point average)

· Make decisions (determine availability of ordered products)

· Sort, filter or otherwise summarize data (identify overdue invoices)

· Organize data into useful information (e.g., generate a report or answer a question)

· Trigger other processes (e.g., turn on the furnace or instruct a robot)

· Use stored data (create, read, update or delete a record)

Guidelines of the process:

1. Name of the process consists of a verb and noun, which reflects the function of the process
2. Do not use the process as part of the name of a bubble
3. May not have some process that has the same name
4. 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

The Process Symbol
Processes transform or manipulate data. Each box has a unique number as identifier (top left) and a unique name (an imperative - e.g. 'do this' - statement in the main box area) The top line is used for the location of, or the people responsible for, the process.
Processes are 'black boxes' - we don't know what is in them until they are decomposed
Processes transform or manipulate input data to produce output data. Except in rare cases, you can't have one without the other.

DFD Levels

The Context and Top Level diagrams in the example start to describe 'Home Catalogue' type sales system. The two diagrams are just the first steps in creating a model of the system. (By model we mean a co-ordinated set of diagrams which describe the target system and provide answers to questions we need to ask about that system).As suggested the diagrams presented in the example will be reworked and amended many times - until all parties are satisfied. But the two diagrams by themselves are not enough; they only provide a high level description. On the other hand, the initial diagrams do start to break down, decompose, what might be quite a complex system into manageable parts.

A revision of the example Top Level DFD

The next step - the Next Level(s)

Each Process box in the Top Level diagram will itself be made up of a number of processes, and will need to be decomposed as a second level diagram.

Decomposition stops when a process box can be described with an Elementary Process Description using ordinary English, later on the process will be described more formally as a Function Description using, for example, pseudocode.

DATA STORAGE

Data Stores are some location where data is held temporarily or permanently.
In physical DFDs there can be 4 types.
D = computerised Data
M = Manual, e.g. filing cabinet.
T = Transient data file, e.g. temporary program file
T(M) = Transient Manual, e.g. in-tray, mail box.
As with external entities, it is common practice to have duplicates of data stores to make a diagram less cluttered

DFD SYMBOLS

DATA DICTIONARY
A data dictionary is a collection of descriptions of the data objects or items in a data model for the benefit of programmers and others who need to refer to them. A first step in analyzing a system of objects with which users interact is to identify each object and its relationship to other objects. This process is called data modeling and results in a picture of object relationships. After each data object or item is given a descriptive name, its relationship is described (or it becomes part of some structure that implicitly describes relationship), the type of data (such as text or image or binary value) is described, possible predefined values are listed, and a brief textual description is provided. This collection can be organized for reference into a book called a data dictionary.

When developing programs that use the data model, a data dictionary can be consulted to understand where a data item fits in the structure, what values it may contain, and basically what the data item means in real-world terms. For example, a bank or group of banks could model the data objects involved in consumer banking. They could then provide a data dictionary for a bank's programmers. The data dictionary would describe each of the data items in its data model for consumer banking (for example, "Account holder" and ""Available credit").

BALANCING IN DATA FLOW DIAGRAM
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 it. 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:
1. There must be a balance between input and output of one level and the next level.
2. 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.
3. Name of the flow of data, data storage and terminals at each level must be the same if its object same.

PROHIBITION IN DFD

1. Data flow may not from external entity directing to external entity another without via a process

2. Data flow may not of direct data storage make towards external entity without via a process

3. Data flow may not of direct data storage wend another data trove without via a process

4. Data flow of one process directing to wend another process without via an advisable data storage / one can maybe be avoided

Refrences:

ER Ngurah Agus Sanjaya, S.KOM, M.KOM. Slide Part 4 - DATA FLOW DIAGRAM.

HM, Jogiyanto. 2005. Analisis & Desain Sistem Informasi. Yogyakarta: ANDI.

http://www.edrawsoft.com/Data-Flow-Diagram-Symbols.php

http://www.cems.uwe.ac.uk/~tdrewry/dfds.htm

http://searchsoa.techtarget.com/sDefinition/0,,sid26_gci211896,00.html

http://facweb.cs.depaul.edu/yele/Course/IT215/DFD%20Mechanics.ppt

4th Quiz

FIRST OBSERVATION AND ANALYSIS REQUIREMENT

INVESTIGATION SYSTEM CONCEPT

There are some point about Investigation System Concept, which the following:

1. Discrepancy between the objective of system and the real condition of system
2. Problem detection report is not real, because:

a. A goal that is too ideal, too difficult to achieve

b. Lack of resources and or attitude

c. Measurement system is less accurate

d. System that is the purpose behind Goal system that is out of date

e. The difference between the system and the system idel while

3. Problem solving:

a. Investigation to the system that is running

b. Description of the condition of the system that runs through it in detail

c. Getting a consensus that the ideal system

d. Developed several alternative

e. Select the best alternative
4. For the purpose of the investigation indicate that problems are actually happening

PROBLEMS IN INVESTIGATION SYSTEM

Investigations in several problems that often appear are:

1. Time

2. Cost

3. Knowledge

4. Politic

5. Intervention

RECOMMENDATION

A result from investigation is a recomendation, that are:

a. Does not take any action if the problem does not exist
b. Perform system maintenance for a small problem

c. Increasing the ability or skills to use the system

d. Consider modifications to total system

e. Putting the problem to occur in the development plan system is carried out immediately

INVESTIGATION TACTICS

Investigation tactics is important because that able to:

a. find a problem or issues

b. knowing the causes of the emergence of problems

c. determining the right solution

Some of the tactics that can be done:

a. Listen to opinions the subject of system
b. Don't give an early breakthrough
c. Compare the stories from the subject of system concerning in the same case

d. Note the logical inconsistency problem

INVESTIGATION TECHIQUE

Directly:

a. The questionnaire

b. discussion

c. Observation

Indirectly

a. Flow of the procedure

b. Reviewing documents

c. Sample

d. Tabular

RECENTLY SYSTEM DESCRIPTION

a. Inputs

b. Outputs

c. Files

d. Data elements

e. Transaction and document action volume

f. Data flow diagrams

ANALYSIS NEEDS

Stage of intensive interaction between the systems analyst with the end user where the system development team show their expertise to get feedback and trust so that the user get a good participation.

FOUR OBJECTIVES THAT WANT TO ACHIEVED

1. Explain the complete system

2. Information system that describes the ideal

3. Bringing information system to the ideal conditions at this time with attention to resource constraints

4. Providing encouragement to the user's confidence in the system development

METHOD NEED ANALYSIS

a. FAQ
b. Kuisioner
c. Observation
d. Analysis procedure
e. Document observation

RESOURCES PROBLEMS

a. Time
b. Money
c. Expertise
d. Technology
e. External Factors

DOCUMENT ANALYSIS NEEDS

– Analysis brief : relation with end user, process monitoring, data collect problem

– User needs : truly needs, report needs, training needs and new system effect.

– System problem : explain time and cost problem, skill, technology and external factor.

– Documents, data collect instrument, statistic consensus, physical and logical data flow, starting data element on data dictionary.

GENERATING SYSTEMS ALTERNATIVES

How to approach the condition of the system at this time with the condition of the ideal system?

- Create an alternative to solve the problem of information system
- The best alternative is applied wisely

OPTION STRATEGIES

- Distributed versus centralized processing

Changes in decision-making information from the centralized data processing to the end user Decentralized responsibility center

- Integrated versus dispersed database

System designer must consider the data are entered in the data base and into the file

- Surround Strategy of System Development

About important environmental strategy in the case of company takeovers because the

information system of other companies may vary with the company at this time.

TACTICAL OPTION

- The design is done before the selection operation

OPERATIONAL DESIGN OPTIONS

1. Input

a. Online Vs Off Line Data Entry

b. Keyed Vs Machine Readable Data Entry

c. Centralized Vs Decentralized Data Entry

2. Process

a. Batch Vs Realtime record update

b. Sequential Vs Direct Access to records

c. Single Vs Multiple User update of records

3. Output

a. Traditional Vs Turn Around Documents

b. Structured Vs Inquiry based reports

SELECTING THE PROPER SYSTEM

1. Compare tactics: systems based on the comparison of costs and benefits relative; There are 3 ways the system "A" said the system is superior to the other if :

- "A" has a cost lower than "B" and their profit same.

- "A" has a cost lower than "B" and "A" result in more profits from the "B"

- "A" and "B" have the same costs but the resulting benefit "A" more.

2. Some methods of comparison system
- Break Even point Analyisis
- Payback Period
- Discounted PayBack period
- Internal Rate of Return

3. Category Cost
- Hardware
- Software
- People
- Suppliers
- Teleccommunications
- Physical sites

4. Fee Details
Comparing the cost of information systems through the life of the system, analysis is calculating the cost changes for the future and there are 3 models of cost of information system, namely Linear, and exponentially Step Function.

5. Cost of information system can occur only once and can also occur continously.
- The cost of information systems that occur only once is ontime cost and development cost that occur during the development of the system.
- The cost of information systems that occur on a continual basis are reccuring cost and operational cost where the cost of this is happened when the information system operates every day.

THE INFORMATION SYSTEM FACTORS

Qualitative factors that lead the performance information system that both of them:

1. Reduce errors

2. Reducing the time to fix errors

3. Reduce the response time from the workstation alternative

4. Accelerate the time of providing information

5. Improve security systems

6. Propagate update records on the source

7. Increasing user satisfaction

THE COMPANY STRATEGY FACTORS

a. Costumer satisfaction

b. Increase sales level

c. Consumer and vendor commitment

d. Product marketing information

SYSTEM PRESENTATION LEARNING

- Conduct a brief presentation
– Deduct detail explain technic

– Specific presentation with visual auxiliary

– If using a model, use auxiliary like laptop so making more informative

– Focus with advantage from information system suggestion with some existing alternative which appropriate with company condition.

CONTINUING THE DECISION OR NOT

– If the company decide to developmney the system, then information department will do next process,its a design process sistem.

– If not, the System Development Life Cycle (SDLC) will be stop.

– Frequently will be found problem with studying system and generally top management will ask to re-working with studying system

– Model will explain some stage part which repeat and sometimes information department will make decision repeating the stage before explain studying system

– With alternative, decision for repeating a SDLC stage previously or not is called Go–No–Go Decision

Reffrence:

Slide PPT Pengamatan Awal, Kebutuhan Analisis; Ngurah Agus Sanjaya ER, S.Kom, M.Kom.