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

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

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

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

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.

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

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

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

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.

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

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.

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.

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.

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.

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

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

Example of Context Diagram

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

Example of DFD Level 1

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

Example Level 2 DFD from the monitor sensors process

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.

Example A balanced DFD Fragment source: www.yourdon.com

Example An out-of-balance DFD Fragment Source: www.yourdon.com

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

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