1. Data Flow Diagram, Data Dictionary, and Process Specification PART I
PI2134 Software Engineering
IT Telkom

2. Chapter Objectives
Describe data and process modeling concepts and tools, including data flow diagrams, a data dictionary, and process descriptions
Describe the symbols used in data flow diagrams and explain the rules for their use
Draw data flow diagrams in a sequence, from general to specific 3

3. Chapter Objectives
Explain how to level and balance a set of data flow diagrams
Describe how a data dictionary is used and what it contains
Describe how a process specification is used and what it contains 3

4. Outline (this meeting)
Definition
DFD Symbols
Data Flow Diagram Layers
Creating Set of DFDs

5. Data Flow Diagrams
A data flow diagram (DFD) shows how data moves through an information system but does not show program logic or processing steps
Data flow diagrams illustrate how data is processed by a system in terms of inputs and outputs.

6. Data Flow Diagrams
A set of DFDs provides a logical model that shows what the system does, not how it does it

7. The Symbols
DFDs use four basic symbols that represent processes, data flows, data stores, and entities
Gane and Sarson symbol set
Yourdon symbol set

8. Process
Process Notations                           Yourdon and Coad Process Notations                 
A process transforms incoming data flow into outgoing data flow.
Receives input data and produces output that has a different content, form, or both
Contain the business logic, also called business rules
Referred to as a black box
Gane and Sarson Process Notation

9. Data Flow
Data flows are pipelines through which packets of information flow.
Represents one or more data item
The symbol for a data flow is a line with a single or double arrowhead
Label the arrows with the name of the data that moves through it.

10. Data Store Data stores are repositories of data in the system.
Datastore Notations                  Yourdon and Coad Datastore Notations                                   Gane and Sarson Datastore Notations
Data stores are repositories of data in the system.
They are sometimes also referred to as files.
Represent data that the system stores
The physical characteristics of a data store are unimportant because you are concerned only with a logical model

11. External Entity
External entities are objects outside the system, with which the system communicates.
External entities are sources and destinations of the system's inputs and outputs.

12. DFD Layers Draw data flow diagrams in several nested layers.
A single process node on a high level diagram can be expanded to show a more detailed data flow diagram.
Draw the context diagram first, followed by various layers of data flow diagrams.

13. Context Diagrams
A context diagram is a top level (also known as Level 0) data flow diagram.
It only contains one process node (process 0) that generalizes the function of the entire system in relationship to external entities.

14. DFD levels
The first level DFD shows the main processes within the system.
Each of these processes can be broken into further processes until you reach pseudocode.

15. Creating a Set of DFDs
Create a graphical model of the information system based on your fact-finding results
Performing three main tasks
Step 1: Draw a context diagram
Step 2: Draw a DFD level 1
Step 3: Draw the lower-level diagrams

16. Draw a Context Diagram Drawing Guidelines
Draw the context diagram so it fits on one page
Use the name of the information system as the process name in the context diagram
Use unique names within each set of symbols
Do not cross lines
Provide a unique name and reference number for each process
Obtain user input and feedback

17. Example of Context Diagram

18. Draw a DFD Level 1
Zooms in on the context diagram and shows major processes, data flows, and data stores
Must retain all the connections that flow into and out of process
Each process has a reference number
Diverging data flow

19. Example of DFD Level 1

20. Draw the Lower-Level Diagrams
Must use leveling and balancing techniques
Leveling
Uses a series of increasingly detailed DFDs to describe an information system
Exploding, partitioning, or decomposing

21. Example
Level 2 DFD from the monitor sensors process

22. Balancing
Ensures that the input and output data flows of the parent DFD are maintained on the child DFD
Simple rule: the dataflows coming into and going out of a bubble at one level must correspond to the dataflows coming into and going out of an entire figure at the next lower level which describes that bubble.

23. Example
A balanced DFD Fragment
source:

24. Example
An out-of-balance DFD Fragment
Source:

25. Review Definition DFD Symbols Data Flow Diagram Layers
Creating Set of DFDs

26. Buatlah DFD tentang Sistem Informasi Rumah Sakit
Buatlah DFD sampai level 2